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Medical Patent Abstract
A system and method for positioning a medical instrument at a desired
biological target tissue site is provided. The system includes an
elongated sheath having a deflectable distal end configured to deflect
or otherwise position at least a portion of a medical instrument
during a surgical procedure allowing for the placement of the deflected
portion adjacent or proximate to a predetermined target tissue surface.
The positioning system may be incorporated into the medical instrument.
The medical instrument may be an ablation system.
Medical Patent Claims
What is claimed is:
1. A method of positioning a medical instrument within a patient's
body using a guide sheath having a sharp tip at a deflectable distal
end during a surgical procedure, comprising the steps of: introducing
into the patient's body the guide sheath having the deflectable
distal end and having a longitudinal axis and at least one lumen
passing therethrough that is aligned along the longitudinal axis
near the distal end; dissecting tissue with the sharp tip; deflecting
the deflectable distal end of the sheath within the patient's body;
introducing the medical instrument into the guide sheath positioned
within the patient's body toward a target tissue site; and advancing
the distal end of the medical instrument through the at least one
lumen to the deflectable distal end thereof for positioning at least
a portion of the medical instrument within the deflected distal
end of the guide sheath near the target tissue site.
2. The method of claim 1 wherein deflecting the deflectable distal
end includes deflecting by an angular amount skewed from the longitudinal
axis of about 180.degree..
3. The method of claim 1 wherein dissecting tissue comprises advancing
the sharp tip to extend distally past the deflectable distal end.
4. The method of claim 1 wherein the medical instrument includes
a tissue-ablating element and the method further comprises positioning
the tissue-ablating element within the deflectable distal end.
Medical Patent Description
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates, generally, to ablation instrument
systems that use ablative energy to ablate internal bodily tissues.
More particularly, to preformed guide apparatus which cooperate
with energy delivery arrangements to direct the ablative energy
in selected directions along the guide apparatus.
2. Description of the Prior Art
It is well documented that atrial fibrillation, either alone or
as a consequence of other cardiac disease, continues to persist
as the most common cardiac arrhythmia. According to recent estimates,
more than two million people in the U.S. suffer from this common
arrhythmia, roughly 0.15% to 1.0% of the population. Moreover, the
prevalence of this cardiac disease increases with age, affecting
nearly 8% to 17% of those over 60 years of age.
Atrial arrhythmia may be treated using several methods. Pharmacological
treatment of atrial fibrillation, for example, is initially the
preferred approach, first to maintain normal sinus rhythm, or secondly
to decrease the ventricular response rate. Other forms of treatment
include drug therapies, electrical cardioversion, and RF catheter
ablation of selected areas determined by mapping. In the more recent
past, other surgical procedures have been developed for atrial fibrillation,
including left atrial isolation, transvenous catheter or cryosurgical
ablation of His bundle, and the Corridor procedure, which have effectively
eliminated irregular ventricular rhythm. However, these procedures
have for the most part failed to restore normal cardiac hemodynamics,
or alleviate the patient's vulnerability to thromboembolism because
the atria are allowed to continue to fibrillate. Accordingly, a
more effective surgical treatment was required to cure medically
refractory atrial fibrillation of the Heart.
On the basis of electrophysiologic mapping of the atria and identification
of macroreentrant circuits, a surgical approach was developed which
effectively creates an electrical maze in the atrium (i.e., the
MAZE procedure) and precludes the ability of the atria to fibrillate.
Briefly, in the procedure commonly referred to as the MAZE III procedure,
strategic atrial incisions are performed to prevent atrial reentry
circuits and allow sinus impulses to activate the entire atrial
myocardium, thereby preserving atrial transport function postoperatively.
Since atrial fibrillation is characterized by the presence of multiple
macroreentrant circuits that are fleeting in nature and can occur
anywhere in the atria, it is prudent to interrupt all of the potential
pathways for atrial macroreentrant circuits. These circuits, incidentally,
have been identified by intraoperative mapping both experimentally
and clinically in patients.
Generally, this procedure includes the excision of both atrial
appendages, and the electrical isolation of the pulmonary veins.
Further, strategically placed atrial incisions not only interrupt
the conduction routes of the common reentrant circuits, but they
also direct the sinus impulse from the sinoatrial node to the atrioventricular
node along a specified route. In essence, the entire atrial myocardium,
with the exception of the atrial appendages and the pulmonary veins,
is electrically activated by providing for multiple blind alleys
off the main conduction route between the sinoatrial node to the
atrioventricular node. Atrial transport function is thus preserved
postoperatively as generally set forth in the series of articles:
Cox, Schuessler, Boineau, Canavan, Cain, Lindsay, Stone, Smith,
Corr, Change, and D'Agostino, Jr., The Surgical Treatment Atrial
Fibrillation (pts. 1-4), 101 THORAC CARDIOVASC SURG., 402-426, 569-592
(1991).
While this MAZE III procedure has proven effective in ablating
medically refractory atrial fibrillation and associated detrimental
sequelae, this operational procedure is traumatic to the patient
since this is an open-heart procedure and substantial incisions
are introduced into the interior chambers of the Heart. Consequently,
other techniques have been developed to interrupt atrial fibrillation
restore sinus rhythm. One such technique is strategic ablation of
the atrial tissues through ablation catheters.
Most approved ablation catheter systems now utilize radio frequency
(RF) energy as the ablating energy source. Accordingly, a variety
of RF based catheters and power supplies are currently available
to electrophysiologists. However, radio frequency energy has several
limitations including the rapid dissipation of energy in surface
tissues resulting in shallow "burns" and failure to access
deeper arrhythmic tissues. Another limitation of RF ablation catheters
is the risk of clot formation on the energy emitting electrodes.
Such clots have an associated danger of causing potentially lethal
strokes in the event that a clot is dislodged from the catheter.
It is also very difficult to create continuous long lesions with
RF ablation instruments.
As such, catheters which utilize other energy sources as the ablation
energy source, for example in the microwave frequency range, are
currently being developed. Microwave frequency energy, for example,
has long been recognized as an effective energy source for heating
biological tissues and has seen use in such hyperthermia applications
as cancer treatment and preheating of blood prior to infusions.
Accordingly, in view of the drawbacks of the traditional catheter
ablation techniques, there has recently been a great deal of interest
in using microwave energy as an ablation energy source. The advantage
of microwave energy is that it is much easier to control and safer
than direct current applications and it is capable of generating
substantially larger and longer lesions than RF catheters, which
greatly simplifies the actual ablation procedures. Such microwave
ablation systems are described in the U.S. Pat. No. 4,641,649 to
Walinsky; U.S. Pat. No. 5,246,438 to Langberg; U.S. Pat. No. 5,405,346
to Grundy, et al.; and U.S. Pat. No. 5,314,466 to Stern, et al,
each of which is incorporated herein by reference.
Most of the existing microwave ablation catheters contemplate the
use of longitudinally extending helical antenna coils that direct
the electromagnetic energy in all radial directions that are generally
perpendicular to the longitudinal axis of the catheter. Although
such catheter designs work well for a number of applications, such
radial output is inappropriate when the energy needs to be directed
toward the tissue to ablate only.
Consequently, microwave ablation instruments have recently been
developed which incorporate microwave antennas having directional
reflectors. Typically, a tapered directional reflector is positioned
peripherally around the microwave antenna to direct the waves toward
and out of a window portion of the antenna assembly. These ablation
instruments, thus, are capable of effectively transmitting electromagnetic
energy in a more specific direction. For example, the electromagnetic
energy may be transmitted generally perpendicular to the longitudinal
axis of the catheter but constrained to a selected radial region
of the antenna, or directly out the distal end of the instrument.
Typical of these designs are described in the U.S. patent application
Ser. Nos. 09/178,066, filed Oct. 23, 1998; and 09/333,747, filed
Jun. 14, 1999, each of which is incorporated herein by reference.
In these designs, the resonance frequency of the microwave antenna
is preferably tuned assuming contact between the targeted tissue
or blood and a contact region of the antenna assembly extending
longitudinally adjacent to the antenna longitudinal axis. Hence,
should a portion of, or substantially all of, the exposed contact
region of the antenna not be in contact with the targeted tissue
or blood during ablation, the resonance frequency will be adversely
changed and the antenna will be untuned. As a result, the portion
of the antenna not in contact with the targeted tissue or blood
will radiate the electromagnetic radiation into the surrounding
air. The efficiency of the energy delivery into the tissue will
consequently decrease which in turn causes the penetration depth
of the lesion to decrease.
This is particularly problematic when the microwave antenna is
not in the blood pool, or when the tissue surfaces are substantially
curvilinear, or when the targeted tissue for ablation is difficult
to access, such as in the interior chambers of the Heart. Since
these antenna designs are generally relatively rigid, it is often
difficult to maneuver substantially all of the exposed contact region
of the antenna into abutting contact against the targeted tissue.
In these instances, several ablation instruments, having antennas
of varying length and shape, may be necessary to complete just one
series of ablations.
SUMMARY OF THE INVENTION
Accordingly, a system for ablating a selected portion of a contact
surface of biological tissue is provided. The system is particularly
suitable to ablate cardiac tissue, and includes an elongated ablation
sheath having a preformed shape adapted to substantially conform
a predetermined surface thereof with the contact surface of the
tissue. The ablation sheath defines an ablation lumen extending
therethrough along an ablation path proximate to the predetermined
surface. An elongated ablative device includes a flexible ablation
element which cooperate with an ablative energy source which is
sufficiently strong for tissue ablation. The ablative device is
formed and dimensioned for longitudinal sliding receipt through
the ablation lumen of the ablation sheath for selective placement
of the ablative device along the ablation path created by the ablation
sheath. The ablation lumen and the ablative device cooperate to
position the ablative device proximate to the ablation sheath predetermined
surface for selective ablation of the selected portion.
Accordingly, the ablation sheath in its preshaped form functions
as a guide device to guide the ablative device along the ablation
path when the predetermined surface of the ablation sheath properly
contacts the biological tissue. Further, the cooperation between
the ablative device and the ablation lumen, as the ablative device
is advanced through the lumen, positions the ablative device in
a proper orientation to facilitate ablation of the targeted tissue
during the advancement. Thus, once the ablation sheath is stationed
relative the targeted contact surface, the ablative device can be
easily advanced along the ablation path to generate the desired
tissue ablations.
In one embodiment, the ablative device is a microwave antenna assembly
which includes a flexible shield device coupled to the antenna substantially
shield a surrounding area of the antenna from the electromagnetic
field radially generated therefrom while permitting a majority of
the field to be directed generally in a predetermined direction
toward the ablation sheath predetermined surface. The microwave
antenna assembly further includes a flexible insulator disposed
between the shield device and the antenna. A window portion of the
insulator is defined which enables transmission of the directed
electromagnetic field in the predetermined direction toward the
ablation sheath predetermined surface. The antenna, the shield device
and the insulator are formed for manipulative bending thereof, as
a unit, to one of a plurality of contact positions to generally
conform the window portion to the ablation sheath predetermined
surface as the insulator and antenna are advanced through the ablation
lumen.
In another embodiment, to facilitate alignment of the ablative
device assembly in the ablation lumen, the ablative device provides
a key device which is slidably received in a mating slot portion
of the ablation lumen. In still another embodiment, the system includes
a guide sheath defining a guide lumen formed and dimensioned for
sliding receipt of the ablation sheath therethrough. The guide sheath
is pre-shaped to facilitate positioning of the ablation sheath toward
the selected portion of the contact surface when the ablation sheath
is advanced through guide lumen.
The ablation sheath includes a bendable shape retaining member
extending longitudinally therethrough which is adapted to retain
the preformed shape of the ablation sheath once positioned out of
the guide lumen of the guide sheath.
The ablative energy is preferably provided by a microwave ablative
device. Other suitable tissue ablation devices, however, include
cryogenic, ultrasonic, laser and radiofrequency, to name a few;
In another aspect of the present invention, a method for treatment
of a Heart includes forming a penetration through a muscular wall
of the Heart into an interior chamber thereof; and positioning a
distal end of an elongated ablation sheath through the penetration.
The ablation sheath defines an ablation lumen extending along an
ablation path therethrough. The method further includes contacting,
or bringing close enough, a predetermined surface of the elongated
ablation sheath with a first selected portion of an interior surface
of the muscular wall; and passing a flexible ablative device through
the ablation lumen of the ablation sheath for selective placement
of the ablative device along the ablation path. Once these events
have been performed, the method includes applying the ablative energy,
using the ablative device and the ablation energy source, which
is sufficiently strong to cause tissue ablation.
In one embodiment, the passing is performed by incrementally advancing
the ablative device along a plurality of positions of the ablation
path to produce a substantially continuous lesion. Before the positioning
event, the method includes placing a distal end of a guide sheath
through the penetration, and then positioning the distal end of
the ablation sheath through the guide lumen of the guide sheath.
In still another embodiment, before the placing event, piercing
the muscular wall with a piercing sheath. The piercing sheath defines
a positioning passage extending therethrough, The placing the distal
end of a guide sheath is performed by placing the guide sheath distal
end through the positioning passage of the piercing sheath.
In yet another configuration, the positioning the distal end event
includes advancing the ablation sheath toward the first selected
portion of the interior surface of the muscular wall through a manipulation
device extending through a second penetration into the Heart interior
chamber independent from the first named penetration.
In another embodiment, a system for ablating tissue within a body
of a patient is provided including an elongated rail device and
an ablative device. The radial device is adapted to be positioned
proximate and adjacent to a selected tissue region to be ablated
within the body of the patient. The ablative device includes a receiving
passage configured to slideably receive the rail device longitudinally
therethrough. This enables the ablative device to be slideably positioned
along the rail substantially adjacent to or in contact with the
selected tissue region. The ablative device, having an energy delivery
portion which is adapted to be coupled to an ablative energy source,
can then be operated to ablate the selected tissue region.
In this configuration, the ablative device is adapted to directionally
emit the ablative energy from the energy delivery portion. A key
assembly cooperates between the ablative device and the rail member,
thus, to properly align the directionally emitted ablative energy
toward the tissue region to be ablated. This primarily performed
by providing a rail device with a non-circular transverse cross-sectional
dimension. The receiving passage of the ablative device further
includes a substantially similarly shaped non-circular transverse
cross-section dimension to enable sliding of the ablative device
in a manner continuously aligning the directionally emitted ablative
energy toward the tissue region to be ablated as the ablative device
advances along the rail device.
BRIEF DESCRIPTION OF THE DRAWINGS
The assembly of the present invention has other objects and features
of advantage which will be more readily apparent from the following
description of the best mode of carrying out the invention and the
appended claims, when taken in conjunction with the accompanying
drawing, in which:
FIGS. 1A and 1B are fragmentary, top perspective views, partially
broken-away, of the ablation system constructed in accordance with
the present invention, and illustrating advancement of a bendable
directional reflective microwave antenna assembly through an ablation
lumen of a ablation sheath.
FIGS. 2A-2D is series of fragmentary, side elevation views, in
partial cross-section, of the Heart, and illustrating advancement
of the ablation system of present invention into the left atrium
for ablation of the targeted tissue.
FIG. 3 is a fragmentary, side elevation view, in partial cross-section,
of the Heart showing a pattern of ablation lesions to treat atrial
fibrillation.
FIGS. 4A and 4B are a series of enlarged, fragmentary, top perspective
view of a pigtail ablation sheath of the ablation system of FIGS.
2C and 2D, and exemplifying the ablation sheath being advanced into
one of the pulmonary vein orifices.
FIG. 5 is a front schematic view of a patient's cardiovascular
system illustrating the positioning of a trans-septal piercing sheath
through the septum wall of the patient's Heart.
FIG. 6 is a fragmentary, side elevation view, in partial cross-section,
of another embodiment of the ablation sheath of the present invention
employed for lesion formation.
FIG. 7 is a fragmentary, side elevation view, in partial cross-section,
of yet another embodiment of the ablation sheath of the present
invention employed for another lesion formation.
FIG. 8 is an enlarged, front elevation view, in cross-section,
of the ablation system of FIG. 1 positioned through the trans-septal
piercing sheath.
FIG. 9 is an enlarged, front elevation view, in cross-section,
of the ablation sheath and the antenna assembly of the ablation
system in FIG. 8 contacting the targeted tissue.
FIG. 10 is an enlarged, front elevation view, in cross-section,
of the antenna assembly taken substantially along the plane of the
line 10-10 in FIG. 9.
FIG. 11 is a diagrammatic top plan view of an alternative embodiment
microwave ablation instrument system constructed in accordance with
one embodiment of the present invention.
FIG. 12 is an enlarged, fragmentary, top perspective view of the
ablation instrument system of FIG. 11 illustrated in a bent position
to conform to a surface of the tissue to be ablated.
FIGS. 13A-13D is a series of side elevation views, in cross-section,
of the ablation sheath of the present invention illustrating advancement
of the ablation device incrementally through the ablation sheath
to form plurality of overlapping lesions.
FIG. 14A is a fragmentary, side elevation view of a laser-type
ablation device of the present invention.
FIG. 14B is a front elevation view of the laser-type energy delivery
portion taken along the plane of the line 14B-14B in FIG. 14A.
FIG. 15A is a fragmentary, side elevation view of a cryogenic-type
ablation device of the present invention.
FIG. 15B is a front elevation view of the cryogenic-type energy
delivery portion taken along the plane of the line 15B-15B in FIG.
15A.
FIG. 16 is a fragmentary, side elevation view, in cross-section,
of an ultrasonic-type ablation device of the present invention.
FIG. 17 is an enlarged, fragmentary, top perspective view of an
alternative embodiment ablation sheath having an opened window portion.
FIG. 18 is a fragmentary, side elevation view of an alternative
embodiment ablation assembly employing a rail system.
FIG. 19 is a front elevation view of the energy delivery portion
of the ablation rail system taken along the plane of the line 19-19
in FIG. 18.
FIGS. 20A-20C are cross-sectional views of alternative key systems
in accordance with the present invention.
FIG. 21 is a fragmentary, diagrammatic, front elevation view of
a torso applying one embodiment of the present invention through
a minimally invasive technique.
FIG. 22 is a top plan view, in cross-section of the fragmentary,
diagrammatic, top plan view of the torso of FIG. 21 applying the
minimally invasive technique.
FIGS. 23A-B are side elevation views of a positioning tool used
in accordance with the present invention.
FIG. 23C is an end elevation view of a positioning tool used in
accordance with the present invention.
FIG. 23D is an end elevation view of an alternative embodiment
of a positioning tool used in accordance with the present invention.
FIG. 23E is a side elevation view of an alternative embodiment
of a positioning tool used in accordance with the present invention.
FIG. 24 is a side view of another alternative embodiment of a positioning
tool used in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
While the present invention will be described with reference to
a few specific embodiments, the description is illustrative of the
invention and is not to be construed as limiting the invention.
Various modifications to the present invention can be made to the
preferred embodiments by those skilled in the art without departing
from the true spirit and scope of the invention as defined by the
appended claims. It will be noted here that for a better understanding,
like components are designated by like reference numerals throughout
the various Figures.
Turning generally now to FIGS. 1A-2D, an ablation system, generally
designated 20, is provided for transmurally ablating a targeted
tissue 21 of biological tissue. The system 20 is particularly suitable
to ablate the epicardial or endocardial tissue 40 of the heart,
and more particularly, to treat medically refractory atrial fibrillation
of the Heart. The ablation system 20 for ablating tissue within
a body of a patient includes an elongated flexible tubular member
22 having at least one lumen 25 (FIGS. 1A, 1B, 8 and 9) and including
a pre-shaped distal end portion (E.g., FIGS. 2C, 6 and 7) which
is shaped to be positioned adjacent to or in contact with a selected
tissue region 21 within the body of the patient. An ablative device,
generally designated 26, is configured to be slidably received longitudinally
within the at least one lumen 25, and includes an energy delivery
portion 27 located near a distal end portion of the ablative device
26 which is adapted to be coupled to an ablative energy source (not
shown).
The ablative device is preferably provided by a microwave ablation
device 26 formed to emit microwave energy sufficient to cause tissue
ablation. As will be described in greater detail below, however,
the ablative device energy may be provided by a laser ablation device,
a Radio Frequency (RF) ablation device, an ultrasound ablation device
or a cryoablation device.
The tubular member 22 is in the form of an elongated ablation sheath
having, in a preferred embodiment, a resiliently preformed shape
adapted to substantially conform a predetermined contact surface
23 of the sheath with the targeted tissue region 21. In another
embodiment, the ablation sheath is malleable. Yet, in another embodiment,
the ablation sheath is flexible. The lumen 25 of the tubular member
extends therethrough along an ablation path proximate to the predetermined
contact surface. Preferably, as will be described in more detail
below, the ablative device 26 includes a flexible energy delivery
portion 27 selectively generating an electromagnetic field which
is sufficiently strong for tissue ablation. The energy delivery
portion 27 is formed and dimensioned for longitudinal sliding receipt
through the ablation lumen 25 of the ablation sheath 22 for selective
placement of the energy delivery portion along the ablation path.
The ablation lumen 25 and the ablative device 26 cooperate to position
the energy delivery portion 27 proximate to the ablation sheath
22 predetermined contact surface 23 of the sheath for selective
transmural ablation of the targeted tissue 21 within the electromagnetic
field when the contact surface 23 strategically contacts or is positioned
close enough to the targeted tissue 21.
Accordingly, in one preferred embodiment, the pre-shaped ablation
sheath 22 functions to unidirectionally guide or position the energy
delivery portion 27 of the ablative device 26 properly along the
predetermined ablation path 28 proximate to the targeted tissue
region 21 as the energy delivery portion 27 is advanced through
the ablation lumen 25. By positioning the energy delivery portion
27, which is preferably adapted to emit a directional ablation field,
at one of a plurality of positions incrementally along the ablation
path (FIGS. 1A and 1B) in the lumen 25, a single continuous or plurality
of spaced-apart lesions can be formed. In other instances, the antenna
length may be sufficient to extend along the entire ablation path
28 so that only a single ablation sequence is necessary.
While the method and apparatus of the present invention are applicable
to ablate any biological tissue which requires the formation of
controlled lesions (as will be described in greater detail below),
this ablation system is particularly suitable for ablating endocardial
or epicardial tissue of the Heart. For example, the present invention
may be applied in an intra-coronary configuration where the ablation
procedure is performed on the endocardium of any cardiac chamber.
Specifically, such ablations may be performed on the isthmus to
address atrial flutter, or around the pulmonary vein ostium, electrically
isolating the pulmonary veins, to treat medically refractory atrial
fibrillation (FIG. 3). This procedure requires the precise formation
of strategically placed endocardial lesions 30-36 which collectively
isolate the targeted regions. By way of example, any of the pulmonary
veins may be collectively isolated to treat chronic atrial fibrillation.
The annular lesion isolating one or more than one pulmonary vein
can be linked with another linear lesion joining the mitral valve
annulus. In another example, the annular lesion isolating one or
more than one pulmonary vein can be linked with another linear lesion
joining the left atrium appendage.
In a preferred embodiment, the pre-shaped ablation sheath 22 and
the sliding ablative device 26 may applied to ablate the epicardial
tissue 39 of the Heart 40 as well (FIG. 12). An annular ablation,
for instance, may be formed around the pulmonary vein for electrical
isolation from the left atrium. As another example, the lesions
may be created along the transverse sinus and oblique sinus as part
of the collective ablation pattern to treat atrial fibrillation
for example.
The application of the present invention, moreover, is preferably
performed through minimally invasive techniques. It will be appreciated,
however, that the present invention may be applied through open
chest techniques as well.
Briefly, to illustrate the operation of the present invention,
a flexible pre-shaped tubular member (i.e., ablation sheath 22)
in the form of a pigtail is shown in FIGS. 2C and 2d which is specifically
configured to electrically isolate a pulmonary vein of the Heart
40. The isolating lesions are preferably made on the posterior wall
of the left atrium, around the ostium of one, or more than one of
a pulmonary vein.
In this example and as illustrated in FIGS. 4A and 4B, a distal
end of the pigtail-shaped ablation sheath or tubular member 22 is
positioned into the left superior pulmonary vein orifice 37 from
the left atrium 41. As the ablation sheath 22 is further advanced,
a predetermined contact surface 23 of the ablation sheath is urged
adjacent to or into contact with the endocardial surface of the
targeted tissue region 21 (FIGS. 2D and 4B). Once the ablation sheath
22 is properly positioned and oriented, the ablative device 26 is
advanced through the ablation lumen 25 of the ablation sheath 22
(FIGS. 1A and 1B) which moves the energy delivery portion 27 of
the ablative device along the ablation path. When the energy delivery
portion 27 is properly oriented and positioned in the ablation lumen
25, the directional ablation field may be generated to incrementally
ablate (FIGS. 13A-13D) the epicardial surface of the targeted tissue
21 along the ablation path to isolate the Left Superior Pulmonary
Vein (LIPV)
Accordingly, as shown in FIGS. 13A-13D, as the energy delivery
portion 27 is incrementally advanced through the lumen 25, overlapping
lesion sections 44-44''' are formed by the ablation field which
is directional in one preferred embodiment. Collectively, a continuous
lesion or series of lesions can be formed which essentially three-dimensionally
"mirror" the shape of the contact surface 23 of the ablation
sheath 22 which is positioned adjacent to or in contact with the
targeted tissue region. These transmural lesions may thus be formed
in any shape on the targeted tissue region such as rectilinear,
curvilinear or circular in shape. Further, depending upon the desired
ablation lines pattern, both opened and closed path formation can
be constructed.
Referring now to FIGS. 2A, 2D and 5, a minimal invasive application
of the present invention is illustrated for use in ablating Heart
tissue. By way of example, a conventional trans-septal piercing
sheath 42 is introduced into the femoral vein 43 through a venous
cannula 45 (FIG. 5). The piercing sheath is then intravenously advanced
into the right atrium 46 of the Heart 40 through the inferior vena
cava orifice 47. These piercing sheaths are generally resiliently
pre-shaped to direct a conventional piercing device 48 toward the
septum wall 50. The piercing device 48 and the piercing sheath 42
are manipulatively oriented and further advanced to pierce through
the septum wall 50, as a unit, of access into the left atrium 41
of the Heart 40 (FIG. 2A).
These conventional devices are commonly employed in the industry
for accessing the left atrium or ventricle, and have an outer diameter
in the range of about 0.16 inch to about 0.175 inch, while having
an inner diameter in the range of about 0.09 inch to about 0.135
inch.
Once the piercing device 48 is withdrawn from a positioning passage
51 (FIG. 8) of the piercing sheath 42, a guide sheath 52 of the
ablation system 20 is slidably advanced through the positioning
passage and into a cardiac chamber such as the left atrium 41 thereof
(FIG. 2B). The guide sheath 52 is essentially a pre-shaped, open-ended
tubular member which is inserted into the coronary circulation to
direct and guide the advancing ablation sheath 22 into a selected
cardiac chamber (i.e., the left atrium, right atrium, left ventricle
or right ventricle) and toward the general direction of the targeted
tissue. Thus, the guide sheath 52 and the ablation sheath 22 telescopically
cooperate to position the predetermined contact surface 23 thereof
substantially adjacent to or in contact with the targeted tissue
region.
Moreover, the guide sheath and the ablation sheath cooperate to
increase the structural stability of the system as the ablation
sheath is rotated and manipulated from its proximal end into ablative
contact with the targeted tissue 21 (FIG. 2A). As the distal curved
portions of the ablation sheath 22, which is inherently longer than
the guide sheath, is advanced past the distal lumen opening of the
guide sheath, these resilient curved portions will retain their
original unrestrained shape.
The telescopic effect of these two sheaths is used to position
the contact surface 23 of the ablation sheath 22 substantially adjacent
to or in contact with the targeted tissue. Thus, depending upon
the desired lesion formation, the same guide sheath 52 may be employed
for several different procedures. For example, the lesion 30 encircling
the left superior pulmonary vein ostium and the Left Inferior Pulmonary
Vein Ostium (RIPVO) lesion 31 (FIG. 3) may be formed through the
cooperation of the pigtail ablation sheath 22 and the same guide
sheath 52 of FIGS. 2B and 2D, while the same guide sheath may also
be utilized with a different ablation sheath 22 (FIG. 4) to create
the long linear lesion 34 as shown in FIG. 3.
In contrast, as illustrated in FIG. 7, another guide sheath 52
having a different pre-shaped distal end section may be applied
to direct the advancing ablation sheath 22 back toward the in the
left and right superior pulmonary vein orifices 53, 55. Thus, several
pre-shaped guide sheaths, and the corresponding ablation sheaths,
as will be described, cooperate to create a predetermined pattern
of lesions (E.g., a MAZE procedure) on the tissue.
In the preferred embodiment, the guide sheath 52 is composed of
a flexible material which resiliently retains its designated shape
once external forces urged upon the sheath are removed. These external
forces, for instance, are the restraining forces caused by the interior
walls 56 of the trans-septal piercing sheath 42 as the guide sheath
52 is advanced or retracted therethrough. While the guide sheath
52 is flexible, it must be sufficiently rigid so as to substantially
retain its original unrestrained shape, and not to be adversely
influenced by the ablation sheath 22, as the ablation sheath is
advanced through the lumen of the guide sheath. Such flexible, biocompatible
materials may be composed of braided Pebax or the like having an
outer diameter formed and dimensioned for sliding receipt longitudinally
through the positioning passage 51 of the trans-septal piercing
sheath 42. The outer dimension is therefore preferably cylindrical
having an outer diameter in the range of about 0.09 inch to about
0.145 inch, and more preferably about 0.135'', while having an inner
diameter in the range of about 0.05 inch to about 0.125 inch, and
more preferably about 0.115''. This cylindrical dimension enables
longitudinal sliding receipt, as well as axial rotation, in the
positioning passage 51 to properly place and advance the guide sheath
52. Thus, the dimensional tolerance between the cylindrical-shaped,
outer peripheral wall of the guide sheath 52 and the interior walls
56 of the trans-septal piercing sheath 42 should be sufficiently
large to enable reciprocal movement and relative axial rotation
therebetween, while being sufficiently small to substantially prevent
lateral displacement therebetween as the ablation sheath 22 is urged
into contact with the targeted tissue 21. For example, the dimensional
tolerance between the transverse cross-sectional periphery of the
interior walls 56 of the positioning passage 51 and that of the
substantially conforming guide sheath 52 should be in the range
of about 0.005 inches to about 0.020 inches.
To increase the structural integrity of the guide sheath 52, metallic
braids 57 are preferably incorporated throughout the sheath when
the guide sheath is molded to its preformed shape. These braids
57 are preferably provided by 0.002'' wires composed of 304 stainless
steel evenly spaced about the sheath.
Once the guide sheath 52 is properly positioned and oriented relative
the trans-septal sheath 42, the ablation sheath 22 is advanced through
a guide lumen 54 (FIG. 8) of the guide sheath 52 toward the targeted
tissue. Similar to the pre-shaped guide sheath 52, the ablation
sheath 22 is pre-shaped in the form of the desired lesions to be
formed in the endocardial surface of the targeted tissue 21. As
best viewed in FIGS. 2D, 6 and 7, each ablation sheath 52 is adapted
facilitate an ablation in the targeted tissue 21 generally in the
shape thereof. Thus, several pre-shaped ablation sheaths cooperate
to form a type of steering system to position the ablation device
about the targeted tissue. Collectively, a predetermined pattern
of linear and curvilinear lesions (E.g., a MAZE procedure) can be
ablated on the targeted tissue region.
Again, similar to the guide sheath 52, the ablation sheath 22 is
composed of a flexible material which resiliently retains its designated
shape once external forces urged upon the sheath are removed. These
external forces, for instance, are the restraining forces caused
by the interior walls 59 defining the guide lumen 54 of the guide
sheath 52 as the ablation sheath 22 is advanced or retracted therethrough.
Such flexible, biocompatible materials may be composed of Pebax
or the like having an outer diameter formed and dimensioned for
sliding receipt longitudinally through the guide lumen 54 of the
ablation sheath 22. As mentioned, the inner diameter of the guide
lumen 54 is preferably in the range of about 0.050 inch to about
0.125 inch, and more preferably about 0.115'', while the ablation
sheath 26 has an outer diameter in the range of about 0.40 inch
to about 0.115 inch, and more preferably about 0.105''.
The concentric cylindrical dimensions enable longitudinal sliding
receipt, as well as axial rotation, of the ablation sheath 22 in
the guide lumen 54 to properly place and advance the it toward the
targeted tissue 21. Thus, the dimensional tolerance between the
cylindrical-shaped, outer peripheral wall of the ablation sheath
22 and the interior walls 59 of the guide lumen 54 of the guide
sheath 52 should be sufficiently large to enable reciprocal movement
and relative axial rotation therebetween, while being sufficiently
small to substantially prevent lateral displacement therebetween
as the ablation sheath 22 is urged into contact with the targeted
tissue 21. For example, the dimensional tolerance between the transverse
cross-sectional periphery of the guide lumen 54 and that of the
substantially conforming energy delivery portion 27 should be in
the range of about 0.001 inches to about 0.005 inches.
As above-indicated, the pre-shaped ablation sheath 22 facilitates
guidance of the ablative device 26 along the predetermined ablation
path 28. This is primarily performed by advancing the energy delivery
portion 27 of the ablative device 26 through the ablation lumen
25 of the ablation sheath 22 which is preferably off-set from the
longitudinal axis 78 thereof. As best viewed in FIGS. 8 and 9, this
off-set positions the energy delivery portion 27 relatively closer
to the predetermined contact surface 23 of the ablation sheath 22,
and hence the targeted tissue 21. Moreover, when using directional
fields such as those emitted from their energy delivery portion
27, it is important to provide a mechanism for continuously aligning
the directional field of the energy delivery portion 27 with the
tissue 21 targeted for ablation. Thus, in this design, the directional
field must be continuously aligned with the predetermined contact
surface 23 of the ablation sheath 22 as the energy delivery portion
27 is advanced through the ablation lumen 25 since the ablation
sheath contact surface 23 is designated to contact or be close enough
to the targeted tissue.
If the directional field is not aligned correctly, for example,
the energy may be transmitted into surrounding fluids and tissues
designated for preservation rather than into the targeted tissue
region. Therefore, in accordance with another aspect of the present
invention, a key structure 48 (FIGS. 1, 8 and 9) cooperates between
the ablative device 26 and the ablation lumen 25 to orient the directive
energy delivery portion 27 of the ablative device continuously toward
the targeted tissue region 21 as it is advanced through the lumen.
This key structure 48, thus, only allows receipt of the energy delivery
portion 27 in the lumen in one orientation. More particularly, the
key structure 48 continuously aligns a window portion 58 of the
energy delivery portion 27 substantially adjacent the predetermined
contact surface 23 of the ablation sheath 22 during advancement.
This window portion 58, as will be described below, enables the
transmission of the directed ablative energy from the energy delivery
portion 27, through the contact surface 23 of the ablation sheath
22 and into the targeted tissue region. Consequently, the directional
ablative energy emitted from the energy delivery portion will always
be aligned with the contact surface 23 of the ablation sheath 22,
which is positioned adjacent to or in contact with the targeted
tissue region 21, to maximize ablation efficiency. By comparison,
the ablation sheath 22 is capable of relatively free rotational
movement axially in the guide lumen 54 of the guide sheath 52 for
maneuverability and positioning of the ablation sheath therein.
As mentioned, the transverse cross-sectional dimension of the energy
delivery portion 27 is configured for sliding receipt in the ablation
lumen 25 of the ablation sheath 22 in a manner positioning the directional
ablative energy, emitted by the energy delivery portion, continuously
toward the predetermined contact surface 23 of the ablation sheath
22. In one example, as shown in FIGS. 8 and 9, the transverse peripheral
dimensions of the energy delivery portion 27 and the ablation lumen
25 are generally D-shaped, and substantially similar in dimension.
Thus, the window portion 58 of the insulator 61, as will be discussed,
is preferably semi-cylindrical and concentric with the interior
wall 62 defining the ablation lumen 25 of the ablation sheath 22.
It will be appreciated, however, that any geometric configuration
may be applied to ensure unitary or aligned insertion. As another
example, one of the energy delivery portion and the interior wall
of the ablation lumen may include a key member and corresponding
receiving groove, or the like. Such key and receiving groove designs,
nonetheless, should avoid relatively sharp edges to enable smooth
advancement and retraction of the energy delivery portion in the
ablation lumen 25.
This dimension alignment relationship can be maintain along the
length of the predetermined contact surface of the ablation sheath
22 as the energy delivery portion 27 is advanced through the ablation
lumen whether in the configuration of FIGS. 2, 6, 7 or 12. In this
manner, a physician may determine that once the predetermined contact
surface 23 of the ablation sheath 22 is properly oriented and positioned
adjacent or in contact against the targeted tissue 21, the directional
component (as will be discussed) of the energy delivery portion
27 will then be automatically aligned with the targeted tissue as
it is advanced through the ablation lumen 25. Upon selected ablation
by the ablative energy, a series of overlapping lesions 44-44'''
(FIGS. 13A-13D) or a single continuous lesion can then be generated.
It will further be appreciated that the dimensional tolerances
therebetween should be sufficiently large to enable smooth relative
advancement and retraction of the energy delivery portion 27 around
curvilinear geometries, and further enable the passage of gas therebetween.
Since the ablation lumen 25 of the ablation sheath 22 is closed
ended, gases must be permitted to flow between the energy delivery
portion 27 and the interior wall 62 defining the ablation lumen
25 to avoid the compression of gas during advancement of the energy
delivery portion therethrough. Moreover, the tolerance must be sufficiently
small to substantially prevent axial rotation of the energy delivery
portion in the ablation lumen 25 for alignment purposes. The dimensional
tolerance between the transverse cross-sectional periphery of the
ablation lumen and that of the substantially conforming energy delivery
portion 27, for instance, should be in the range of about 0.001
inches to about 0.005 inches.
To further facilitate preservation of the fluids and tissues along
the backside of the ablation sheath 22 (i.e., the side opposite
the contact surface 23 of the sheath), a thermal isolation component
(not shown) is disposed longitudinally along, and substantially
adjacent to, the ablation lumen 25. Thus, during activation of the
ablative device, the isolation component and the directive component
73 of the energy ablation portion 27 cooperate to form a thermal
barrier along the backside of the ablation sheath.
For instance, the isolation component may be provided by an air
filled isolation lumen extending longitudinally along, and substantially
adjacent to, the ablation lumen 25. The cross-sectional dimension
of the isolation lumen may be C-shaped or crescent shaped to partially
surround the ablation lumen 25. In another embodiment, the isolation
lumen may be filled with a thermally refractory material.
In still another embodiment, a circulating fluid, which is preferably
biocompatible, may be disposed in the isolation lumen to provide
to increase the thermal isolation. Two or more lumens may be provided
to increase fluid flow. One such biocompatible fluid providing suitable
thermal properties is saline solution.
Similar to the composition of the guide sheath 52, the ablation
sheath 22 is composed of a flexible bio-compatible material, such
as PU Pellethane, Teflon or polyethylent, which is capable of shape
retention once external forces acting on the sheath are removed.
By way of example, when the distal portions of the ablation sheath
22 are advanced past the interior walls of the guide lumen 54 of
the guide sheath 52, the ablation sheath 22 will return to its preformed
shape in the interior of the Heart.
To facilitate shape retention, the ablation sheath 22 preferably
includes a shape retaining member 63 extending longitudinally through
the distal portions of the ablation sheath where shape retention
is necessary. As illustrated in FIGS. 1, 8 and 9, this retaining
member 63 is generally extends substantially parallel and adjacent
to the ablation lumen 25 to reshape the predetermined contact surface
23 to its desired pre-shaped form once the restraining forces are
removed from the sheath. While this shape-memory material must be
sufficiently resilient for shape retention, it must also be sufficiently
bendable to enable insertion through the guide lumen 54 of the guide
sheath 52. In the preferred form, the shape retaining member is
composed of a superelastic metal, such as Nitinol (NiTi). Moreover,
the preferred diameter of this material should be in the range of
0.020 inches to about 0.050 inches, and more preferably about 0.035
inches.
When used during a surgical procedure, the ablation sheath 22 is
preferably transparent which enables a surgeon to visualize the
position of the energy delivery portion 27 of the ablative device
26 through an endoscope or the like. Moreover, the material of ablation
sheath 22 must be substantially unaffected by the ablative energy
emitted by the energy delivery portion 27. Thus, as will be apparent,
depending upon the type of energy delivery portion and the ablative
source applied, the material of the tubular sheath must exhibit
selected properties, such as a low loss tangent, low water absorption
or low scattering coefficient to name a few, to be unaffected by
the ablative energy.
As previously indicated, the ablation sheath 22 is advanced and
oriented, relative to the guide sheath 52, adjacent to or into contact
with the targeted tissue region 21 to form a series of over-lapping
lesions 44-44''', such as those illustrated in FIGS. 3 and 13A-13D.
Preferably, the contact surface 23 of the pre-shaped ablation sheath
22 is negotiated into physical contact with the targeted tissue
21. Such contact increases the precision of the tissue ablation
while further facilitating energy transfer between the ablation
element and the tissue to be ablated, as will be discussed.
To assess proper contact and positioning of the contact surface
23 of the ablation sheath 22 against the targeted tissue 21, at
least one positioning electrode, generally designated 64, is disposed
on the exterior surface of the ablation sheath for contact with
the tissue. Preferably a plurality of electrodes are positioned
along and adjacent the contact surface 23 to assess contact of the
elongated and three dimensionally shaped contact surface. These
electrodes 64 essentially measure whether there is any electrical
activity (or electrophysiological signals) to one or the other side
of the ablation sheath 22. When a strong electrical activation signal
is detected, or inter-electrode impedance is measured when two or
more electrodes are applied, contact with the tissue can be assessed.
Once the physician has properly situated and oriented the sheath,
they may commence advancement of the energy delivery portion 27
through the ablation lumen 25. Additionally, these positioning electrodes
may be applied to map the biological tissue prior to or after an
ablation procedure, as well as be used to monitor the patient's
condition during the ablation process.
To facilitate discussion of the above aspects of the present invention,
FIG. 10 illustrates two side-by-side electrodes 64, 65 configured
for sensing electrical activity in substantially one direction,
in accordance with one aspect of the present invention. This electrode
arrangement generally includes a pair of longitudinally extending
electrode elements 66, 67 that are disposed on'the outer periphery
of the ablation sheath 22. The pair of electrode elements 66, 67
are positioned side by side and arranged to be substantially parallel
to one another. In general, splitting the electrode arrangement
into a pair of distinct elements permits substantial improvements
in the resolution of the detected electrophysiological signals.
Therefore, the pair of electrode elements 66, 67 are preferably
spaced apart and electrically isolated from one another. It will
be appreciated, however, that only one electrode may be employed
to sense proper tissue contact. It will also be appreciated that
ring or coiled electrodes can also be used.
The pair of electrode elements 66, 67 are further arranged to be
substantially parallel to the longitudinal axis of the ablation
sheath 22. In order to ensure that the electrode elements are sensing
electrical activity in substantially the same direction, the space
between electrodes should be sufficiently small. It is generally
believed that too large space may create problems in determining
the directional position of the catheter and too small a space may
degrade the resolution of the detected electrophysiological signals.
By way of example, the distance between the two pair of electrode
elements may be between about 0.5 and 2.0 mm.
The electrode elements 66, 67 are preferably positioned substantially
proximate to the predetermined contact surface 23 of the ablation
sheath 22. More preferably, the electrode elements 66, 67 are positioned
just distal to the distal end of the predetermined contact surface
23 since it is believed to be particularly useful to facilitate
mapping and monitoring as well as to position the ablation sheath
22 in the area designated for tissue ablation. For example, during
some procedures, a surgeon may need to ascertain where the distal
end of the ablation sheath 22 is located in order to ablate the
appropriate tissues. In another embodiment, the electrode elements
66, 67 may be positioned substantially proximate the proximal end
of the predetermined contact surface 23, at a central portion of
the contact surface 23 or a combination thereof. For instance, when
attempting to contact the loop-shaped ablation sheath 22 employed
to isolate each of left and inferior pulmonary vein orifices 37,
38, a central location of the electrodes along the looped-shape
contact surface 23 may best sense contact with the targeted tissue.
Moreover, while not specifically illustrated, a plurality of electrode
arrangements may be disposed along the ablation sheath as well.
By way of example, a first set of electrode elements may be disposed
distally from the predetermined contact surface, a second set of
electrode elements may be disposed proximally to the contact surface,
while a third set of electrode elements may be disposed centrally
thereof. These electrodes may also be used with other types of mapping
electrodes, for example, a variety of suitable mapping electrode
arrangements are described in detail in U.S. Pat. No. 5,788,692
to Campbell, et al., which is incorporated herein by reference in
its entirety. Although only a few positions have been described,
it should be understood that the electrode elements may be positioned
in any suitable position along the length of the ablation sheath.
The electrode elements 66, 67 may be formed from any suitable material,
such as stainless steel and iridium platinum. The width (or diameter)
and the length of the electrode may vary to some extent based on
the particular application of the catheter and the type of material
chosen. Furthermore, in the preferred embodiment where microwave
is used as the ablative energy, the electrodes are preferably dimensioned
to minimize electromagnetic field interference, for example, the
capturing of the microwave field produced by the antenna. In most
embodiments, the electrodes are arranged to have a length that is
substantially larger than the width, and are preferably between
about 0.010 inches to about 0.025 inches and a length between about
0.50 inch to about 1.0 inch.
Although the electrode arrangement has been shown and described
as being parallel plates that are substantially parallel to the
longitudinal axis of the ablation sheath 22 and aligned longitudinally
(e.g., distal and proximal ends match up), it should be noted that
this is not a limitation and that the electrodes can be configured
to be angled relative to the longitudinal axis of the ablation sheath
22 (or one another) or offset longitudinally. Furthermore, although
the electrodes have been shown and described as a plate, it should
be noted that the electrodes may be configured to be a wire or a
point such as a solder blob.
Each of the electrode elements 66, 67 is electrically coupled to
an associated electrode wire 68, 70 and which extend through ablation
sheath 22 to at least the proximal portion of the flexible outer
tubing. In most embodiments, the electrode wires 68, 70 are electrically
isolated from one another to prevent degradation of the electrical
signal, and are positioned on opposite sides of the retaining member
63. The connection between the electrodes 64, 65 and the electrode
wires 68, 70 may be made in any suitable manner such as soldering,
brazing, ultrasonic welding or adhesive bonding. In other embodiments,
the longitudinal electrodes can be formed from the electrode wire
itself. Forming the longitudinal electrodes from the electrode wire,
or out of wire in general, is particularly advantageous because
the size of wire is generally small and therefore the longitudinal
electrodes elements may be positioned closer together thereby forming
a smaller arrangement that takes up less space. As a result, the
electrodes may be positioned almost anywhere on a catheter or surgical
tool. These associated electrodes are described in greater detail
in U.S. patent application Ser. No. 09/548,331, filed Apr. 12, 2000,
and entitled "ELECTRODE ARRANGE-MENT FOR USE IN A MEDICAL INSTRUMENT",
and incorporated by reference.
Referring now to FIGS. 1, 8, 9 and 11, the ablative device 26 is
preferably in the form of an elongated member, which is designed
for insertion into the ablation lumen 25 of the ablation sheath
22, and which in turn is designed for insertion into a vessel (such
as a blood vessel) in the body of a patient. It will be understood,
however, that the present invention may be in the form of a handheld
instrument for use in open surgical or minimally invasive procedures
(FIG. 12).
The ablative device 26 typically includes a flexible outer tubing
71 (having one or several lumens therein), a transmission line 72
that extends through the flexible tubing 71 and an energy delivery
portion 27 coupled to the distal end of the transmission line 72.
The flexible outer tubing 71 may be made of any suitable material
such as medical grade polyolefins, fluoropolymers, or polyvinylidene
fluoride. By way of example, PEBAX resins from Autochem of Germany
have been used with success for the outer tubing of the body of
the catheter.
In accordance with another aspect of the present invention, the
ablative energy emitted by the energy delivery portion 27 of the
ablative device 26 may be one of several types. Preferably, the
energy delivery portion 27 includes a microwave component which
generates a electromagnetic field sufficient to cause tissue ablation.
As mentioned, as will be discussed in greater detail below, the
ablative energy may also be derived from a laser source, a cryogenic
source, an ultrasonic source or a radiofrequency source, to name
a few.
Regardless of the source of the energy, a directive component cooperates
with the energy source to control the direction and emission of
the ablative energy. This assures that the surrounding tissues of
the targeted tissue regions will be preserved. Further, the use
of a directional field has several potential advantages over conventional
energy delivery structure that generate uniform fields about the
longitudinal axis of the energy delivery portion. For example, in
the microwave application, by forming a more concentrated and directional
electromagnetic field, deeper penetration of biological tissues
is enabled, and the targeted tissue region may be ablated without
heating as much of the surrounding tissues and/or blood. Additionally,
since substantial portions the radiated ablative energy is not emitted
in the air or absorbed in the blood or the surrounding tissues,
less power is generally required from the power source, and less
power is generally lost in the microwave transmission line.
In the preferred form, the energy delivery portion 27 of the ablative
device 26 is an antenna assembly configured to directionally emit
a majority of an electromagnetic field from one side thereof. The
antenna assembly 27, as shown in FIGS. 9 and 11, preferably includes
a flexible antenna 60, for generating the electromagnetic field,
and a flexible reflector 73 as a directive component, for redirecting
a portion of the electromagnetic field to one side of the antenna
opposite the reflector. Correspondingly, the resultant electromagnetic
field includes components of the originally generated field, and
components of the redirected electromagnetic field. During aligned
insertion of the antenna assembly 27 into the ablation lumen 25,
via the key structure 48, the directional field will thus be continuously
aligned toward the contact surface 23 of the ablation sheath 22
as the antenna assembly is incrementally advanced through the ablation
lumen 25.
FIG. 11 illustrates that the proximal end of the antenna 60 is
preferably coupled directly or indirectly to the inner conductor
75 of a coaxial transmission line 72. A direct connection between
the antenna 60 and the inner conductor 75 may be made in any suitable
manner such as soldering, brazing, ultrasonic welding or adhesive
bonding. In other embodiments, antenna 60 can be formed from the
inner conductor 75 of the transmission line 72 itself. This is typically
more difficult from a manufacturing standpoint but has the advantage
of forming a more rugged connection between the antenna and the
inner conductor. As will be described in more detail below, in some
implementations, it may be desirable to indirectly couple the antenna
to the inner conductor through a passive component, such a capacitor,
an inductor or a stub tuner for example, in order to provide better
impedance matching between the antenna assembly and the transmission
line, which is a coaxial cable in the preferred embodiment.
Briefly, the transmission line 72 is arranged for actuating and/or
powering the antenna 60. Typically, in microwave devices, a coaxial
transmission line is used, and therefore, the transmission line
72 includes an inner conductor 75, an outer conductor 76, and a
dielectric material 77 disposed between the inner and outer conductors.
In most instances, the inner conductor 75 is coupled to the antenna
60. Further, the antenna 60 and the reflector 73 are enclosed (e.g.,
encapsulated) in a flexible insulative material thereby forming
the insulator 61, to be described in greater detail below, of the
antenna assembly 27.
The power supply (not shown) includes a microwave generator which
may take any conventional form. When using microwave energy for
tissue ablation, the optimal frequencies are generally in the neighborhood
of the optimal frequency for heating water. By way of example, frequencies
in the range of approximately 800 MHz to 6 GHz work well. Currently,
the frequencies that are approved by the Federal Communication Commission
(FCC) for experimental clinical work includes 915 MHz and 2.45 GHz.
Therefore, a power supply having the capacity to generate microwave
energy at frequencies in the neighborhood of 2.45 GHz may be chosen.
A conventional magnetron of the type commonly used in microwave
ovens is utilized as the generator. It should be appreciated, however,
that any other suitable microwave power source could be substituted
in its place, and that the explained concepts may be applied at
other frequencies like about 434 MHz or 5.8 GHz (ISM band).
In the preferred embodiment, the antenna assembly 27 includes a
longitudinally extending antenna wire 60 that is laterally offset
from the transmission line inner conductor 75 to position the antenna
closer to the window portion 58 of the insulator 61 upon which the
directed electric field is transmitted. The antenna 60 illustrated
is preferably a longitudinally extending exposed wire that extends
distally (albeit laterally offset) from the inner conductor. However
it should be appreciated that a wide variety of other antenna geometries
may be used as well. By way of example, helical coils, flat printed
circuit antennas and other antenna geometries will work as well.
Briefly, the insulator 61 is preferably provided by a good, low-loss
dielectric material which is relatively unaffected by microwave
exposure, and thus capable of transmission of the electromagnetic
field therethrough. Moreover, the insulator material preferably
has a low water absorption so that it is not itself heated by the
microwaves. Incidentally, when the emitted ablative energy is microwave
in origin, the ablation sheath must also include these material
properties. Finally, the insulation material must be capable of
substantial flexibility without fracturing or breaking. Such materials
include moldable TEFLON.RTM., silicone, or polyethylene, polyimide,
etc.
As will be appreciated by those familiar with antenna design, the
field generated by the illustrated antenna will be generally consistent
with the length of the antenna. That is, the length of the electromagnetic
field is generally constrained to the longitudinal length of the
antenna. Therefore, the length of the field may be adjusted by adjusting
the length of the antenna. Accordingly, microwave ablation elements
having specified ablation characteristics can be fabricated by building
them with different length antennas. Additionally, it should be
understood that longitudinally extending antennas are not a requirement
and that other shapes and configurations may be used.
The antenna 60 is preferably formed from a conductive material.
By way of example, copper or silver-plated metal work well. Further,
the diameter of the antenna 60 may vary to some extent based on
the particular application of the catheter and the type of material
chosen. In microwave systems using a simple exposed wire type antenna,
for instance, wire diameters between about 0.010 to about 0.020
inches work well. In the illustrated embodiment, the diameter of
the antenna is about 0.013 inches.
In a preferred embodiment, the antenna 60 is positioned closer
to the area designated for tissue ablation in order to achieve effective
energy transmission between the antenna 60 and the targeted tissue
21 through the predetermined contact surface 23 of the ablation
sheath 22. This is best achieved by placing the antenna 60 proximate
to the outer peripheral surface of the antenna insulator 61. More
specifically, a longitudinal axis of the antenna 60 is preferably
off-set from, but parallel to, a longitudinal axis 78 of the inner
conductor 75 in a direction away from the reflector 73 and therefore
towards the concentrated electromagnetic field (FIGS. 8 and 9).
By way of example, placing the antenna between about 0.010 to about
0.020 inches away from the outer peripheral surface of the antenna
insulator works well. In the illustrated embodiment, the antenna
is about 0.013 inches away from the outer peripheral surface of
the antenna insulator 61. However, it should be noted that this
is not a requirement and that the antenna position may vary according
to the specific design of each catheter.
Referring now to the directive component or reflector 73, it is
positioned adjacent and generally parallel to a first side of the
antenna, and is configured to redirect those components of the electromagnetic
field contacting the reflector back towards and out of a second
side of the antenna assembly 27 opposite the reflector. A majority
of the electromagnetic field, consequently, is directed out of the
window portion 58 of the insulator 61 in a controlled manner during
ablation.
To reduce undesirable electromagnetic coupling between the antenna
and the reflector 73, the antenna 60 is preferably off-set from
the reflector 73 (FIGS. 8 and 9). This off-set from the longitudinal
axis 78 further positions the antenna 60 closer to the window portion
58 to facilitate ablation by positioning the antenna 60 closer to
the targeted tissue region. It has been found that the minimum distance
between the reflector and the antenna may be between about 0.020
to about 0.030 inches, in the described embodiment, in order to
reduce the coupling. However, the distance may vary according to
the specific design of each ablative device.
The proximal end of the reflector 73 is preferably coupled to the
outer conductor 76 of the coaxial transmission line 72. Connecting
the reflector to the outer conductor serves to better define the
electromagnetic field generated during use. That is, the radiated
field is better confined along the antenna, to one side, when the
reflector is electrically connected to the outer conductor of the
coaxial transmission line. The connection between the reflector
73 and the outer conductor 76 may be made in any suitable manner
such as soldering, brazing, ultrasonic welding or adhesive bonding.
In other embodiments, the reflector can be formed from the outer
conductor of the transmission line itself. This is typically more
difficult from a manufacturing standpoint but has the advantage
of forming a more rugged connection between the reflector and the
outer conductor.
In one embodiment, to improve flexibility at the electrical connection
with the outer conductor 76 and entirely along the energy delivery
device, the proximal end of the reflector 73 is directly contacted
against the outer conductor without applying solder or such conductive-adhesive
bonding. In this design, the insulator material of the insulator
61 functions as the adhesive to maintain electrical continuity.
This is performed by initially molding the antenna wire in the silicone
insulator. The reflector 73 is subsequently disposed on the molded
silicone tube, and is extended over the outer conductor 76 of coaxial
cable transmission line 72. A heat shrink tube is then applied over
the assembly to firmly maintain the electrical contact between the
reflector 73 and the coaxial cable outer conductor 76. In other
embodiments, the reflector may be directly coupled to a ground source
or be electrically floating.
As previously noted, the antenna 60 typically emits an electromagnetic
field that is fairly well constrained to the length of the antenna.
Therefore, in some embodiments, the distal end of the reflector
73 extends longitudinally to at about the distal end of the antenna
60 so that the reflector can effectively cooperate with the antenna.
This arrangement serves to provide better control of the electromagnetic
field during ablation. However, it should be noted that the actual
length of the reflector may vary according to the specific design
of each catheter. For example, catheters having specified ablation
characteristics can be fabricated by building catheters with different
length reflectors.
Furthermore, the reflector 73 is typically composed of a conductive,
metallic material or foil. However, since the antenna assembly 27
must be relatively flexible in order to negotiate the curvilinear
ablation lumen 25 of the ablation sheath 22 as the ablative device
it is advanced therethrough, the insulator 61, the antenna wire
and the reflector must collectively be relatively flexible. Thus,
one particularly material suitable for such a reflector is a braided
conductive mesh having a proximal end conductively mounted to the
distal portion of the outer conductor of the coaxial cable. This
conductive mesh is preferably thin walled to the shield assembly
yet provide the appropriate microwave shielding properties, as well
as enable substantial flexibility of the shield device during bending
movement. For example, a suitable copper mesh wire should have a
diameter in the range of about 0.005 inches to about 0.010 inches,
and more preferably about 0.007 inches. A good electrical conductor
is generally used for the shield assembly in order to reduce the
self-heating caused by resistive losses. Such conductors includes,
but are not restricted to copper, silver and gold.
Another suitable arrangement may be thin metallic foil reflector
73 which is inherently flexible. However, to further increase flexibility,
the foil material can be pleated or folded which resists tearing
during bending of the antenna assembly 27. These foils can be composed
of copper that has a layer of silver plating formed on its inner
peripheral surface. Such silver plating, which can also be applied
to the metallic mesh material, is used to increase the conductivity
of the reflector. It should be understood, however, that these materials
are not a limitation. Furthermore, the actual thickness of the reflector
may vary according to the specific material chosen.
Referring back to FIG. 11, the reflector 73 is preferably configured
to have an arcuate or meniscus shape (e.g., crescent), with an arc
angle that opens towards the antenna 60. Flaring the reflector towards
the antenna serves to better define the electromagnetic field generated
during use. Additionally, the reflector functions to isolate the
antenna 60 from the restraining member 63 of the ablation sheath
22 during ablation. Since the restraining member 63 is preferably
metallic in composition (most preferably Nitinol), it is desirable
minimize electromagnetic coupling with the antenna. Thus, the reflector
73 is preferably configured to permit at most a 180.degree. circumferential
radiation pattern from the antenna. In fact, it has been discovered
that arc angles greater than about 180.degree. are considerably
less efficient. More preferably, the arc angle of the radiation
pattern is in the range of about 90.degree. to about 120.degree..
While the reflector is shown and described as having an arcuate
shape, it will be appreciated that a plurality of forms may be provided
to accommodate different antenna shapes or to conform to other external
factors necessary to complete a surgical procedure. For example,
any flared shape that opens towards the antenna may work well, regardless
of whether it is curvilinear or rectilinear.
Further still, it should be noted that the shape of the reflector
need not be uniform. For example, a first portion of the reflector
(e.g., distal) may be configured with a first shape (e.g., 90.degree.
arc angle) and a second portion (e.g., proximal) of the reflector
may be configured with a second shape (e.g., 120.degree. arc angle).
Varying the shape of the reflector in this manner may be desirable
to obtain a more uniform radiated field. It is believed that the
energy transfer between the antenna and the tissue to be ablated
tends to increase by decreasing the coverage angle of the reflector,
and conversely, the energy transfer between the antenna and the
tissue to be ablated tends to decrease by increasing the coverage
angle of the reflector. Accordingly, the shape of the reflector
may be altered to balance out non-uniformities found in the radiated
field of the antenna arrangement.
In another configuration, the directive component 73 for the microwave
antenna assembly 27 can be provided by another dielectric material
having a dielectric constant different than that of the insulator
material 67. Indeed, a strong reflection of electromagnetic wave
is observed when the wave reaches an interface created by two materials
with a different dielectric constant. For example, a ceramic loaded
polymer can have a dielectric constant comprised between 15 and
55, while the dielectric of a fluoropolymer like Teflon or is comprised
between 2 and 3. Such an interface would create a strong reflection
of the wave and act as a semi-reflector.
It should also be noted that the longitudinal length of the reflector
need not be uniform. That is, a portion of the reflector may be
stepped towards the antenna or a portion of the reflector may be
stepped away from the antenna. Stepping the reflector in this manner
may be desirable to obtain a more uniform radiated field. While
not wishing to be bound by theory, it is believed that by placing
the reflector closer to the antenna, a weaker radiated field may
be obtained, and that by placing the reflector further away from
the antenna, a stronger radiated field may be obtained. Accordingly,
the longitudinal length of the reflector may be altered to balance
out non uniformities found in the radiated field of the antenna
arrangement. These associated reflectors are described in greater
detail in U.S. patent application Ser. No. 09/178,066, entitled
"DIRECTIONAL REFLECTOR SHIELD ASSEMBLY FOR A MICROWAVE ABLATION
INSTRUMENT, and Ser. No. 09/484,548 entitled "A MICROWAVE ABLATION
INSTRUMENT WITH FLEXIBLE ANTENNA ASSEMBLY AND METHOD", each
of which is incorporated by reference.
In a typical microwave ablation system, it is important to match
the impedance of the antenna with the impedance of the transmission
line. As is well known to those skilled in the art, if the impedance
is not matched, the catheter's performance tends to be well below
the optimal performance. The decline in performance is most easily
seen in an increase in the reflected power from the antenna toward
the generator. Therefore, the components of a microwave transmission
system are typically designed to provide a matched impedance. By
way of example, a typical set impedance of the microwave ablation
system may be on the order of fifty (50) ohms.
Referring back to FIGS. 10 and 11, and in accordance with one embodiment
of the present invention, an impedance matching device 80 may be
provided to facilitate impedance matching between the antenna 60
and the transmission line 72. The impedance matching device 80 is
generally disposed proximate the junction between the antenna 60
and the inner conductor 75. For the most part, the impedance match
is designed and calculated assuming that the antenna assembly 27,
in combination with the predetermined contact surface 23 of the
ablation sheath 22, is in resonance to minimize the reflected power,
and thus increase the radiation efficiency of the antenna structure.
In one embodiment, the impedance matching device is determined
by using a Smith Abacus Model. In the Smith Abacus Model, the impedance
matching device may be ascertained by measuring the impedance of
the antenna with a network analyzer, analyzing the measured value
with a Smith Abacus Chart, and selecting the appropriate device.
By way of example, the impedance matching device may be any combination
of a capacitor, resistor, inductor, stub tuner or stub transmission
line, whether in series or in parallel with the antenna. An example
of the Smith Abacus Model is described in Reference: David K. Cheng,
"Field and Wave Electromagnetics," second edition, Addison-Wesley
Publishing, 1989, which is incorporated herein by reference. In
one preferred implementation, the impedance matching device is a
serial capacitor having a capacitance in the range of about 0.6
to about 1.0 Pico Farads. In the illustration shown, the serial
capacitor has a capacitance of about 0.8 Pico Farads.
As above-mentioned, the impedance will be matched assuming flush
contact between the antenna assembly 27 and the ablation sheath
(FIG. 9). In accordance with the present invention, as the antenna
assembly 27 is advanced through the ablation lumen 25, before selective
ablation, it is desirable to position the window portion 58 of the
flexible antenna insulator 61 in flush contact against the interior
wall 62 of the ablation lumen 25, opposite the predetermined contact
surface 23. This arrangement may substantially reduce the impedance
variance caused by the interface between insulator 61 and the ablation
sheath 22 as the directional field is transmitted therethrough.
In comparison, if the window portion 58 were not required to be
positioned in flush contact against the interior wall 62 of the
ablation lumen, pockets of air or fluid, or the like, may be disposed
intermittently therebetween which would result in a greater degree
of impedance variations at this interface. Consequently, the above-indicated
impedance matching techniques would be less effective.
To assure such flush contact during selective directional ablation
and advancement along the sheath ablation lumen, the ablation system
20 preferably incorporates a forcing mechanism 81 (FIGS. 8 and 9)
adapted to urge the window portion 58 of the antenna assembly 27
into flush contact against the interior wall 62 of the ablation
sheath. Preferably, the forcing mechanism cooperates between a support
portion 82 of the interior wall 62 of the ablation lumen 25 and
the forcing wall portion 83 of the antenna assembly.
When not operational, the forcing mechanism permits relative axial
displacement between the ablative device 26 and the ablation sheath
for repositioning of the antenna assembly 27 along the ablation
path 28 (FIG. 8). Upon selective operation, the forcing mechanism
81 contacts the forcing wall portion 83 to urge window portion 58
flush against the interior wall 62 opposite the predetermined contact
surface 23. Consequently, the impedance match between the antenna
and the transmission line is properly achieved and stable even when
the antenna is moving in the ablation sheath.
In one embodiment, the forcing mechanism may be provided by an
inflatable structure acting between the support portion 82 of the
interior wall 62 of the ablation lumen 25 and the forcing wall portion
83 of the antenna assembly device. Upon selective inflation of forcing
mechanism 81 (FIG. 9), the window portion 58 will be urged into
flush contact with the interior wall 62 of the ablation lumen. Upon
selective deflation of the forcing mechanism 81 (FIG. 8), relative
axial displacement between the antenna assembly 27 and the ablation
sheath may commence. The forcing mechanism can be provided by other
techniques such as spring devices or the like.
In accordance with another aspect of the present invention, the
ablative energy may be in the form of laser energy sufficient to
ablate tissue. Example of such laser components include CO.sub.2.sub.--or
Nd: YAG lasers. To transmit the beams, the transmission line 72
is preferably in the form of a fiber optic cable or the like.
In this design, as shown in FIGS. 14A and 14B, the directive component
73 may be provided by a reflector having a well polished smooth
reflective or semi-reflective surface. This preferably metallic
reflective surface is configured to reflect the emitted laser energy
toward the targeted tissue region. By way of example, functional
metallic materials include silver or platinum. In another configuration,
similar to the difference in dielectric constants of the microwave
ablation device 26, the directive component of the laser ablative
device may be provided between two layers of dielectric materials
with a sufficient difference between the refractory indexes. Here,
at least one dielectric directive component layer functions like
the outer dielectric layer of the fiber optic transmission line
72 to obtain "total internal reflection". Consequently,
the laser energy can be emitted away fro'm the dielectric layer.
By providing more than one dielectric layer, "total internal
reflection" may be attained at several angles of incidence.
Again, the reflection of the electromagnetic wave is caused by the
interface between two media having different dielectric constants.
Generally speaking, the higher is the difference between the dielectric
constants, the more significant is the internal reflection. In addition,
when more than one dielectric layer are involved, interference can
be used to direct the laser energy in a preferred direction.
Moreover, when the ablative energy is laser based, it will be appreciated
that it is desirable that both the ablation sheath 22 and the ablation
device be composed of materials which have a low scattering coefficient
and a low factor of absorption. In addition, it is also preferable
to use material with low water absorption.
It will be appreciated that a plurality of designs can be used
for the laser energy delivery portion. For example, the laser energy
delivery portion can consist of multiple reflective particles embedded
in a laser transparent material. The laser wave is propagating from
the laser generator to the optic fiber transmission line and enter
in the laser energy delivery portion. The embedded reflective particles
diffracts the light, which is reflected toward the tissue to be
ablated by the directive component 73.
In yet another alternative embodiment, cryogenic energy may be
employed as an ablative energy. Briefly, as shown in FIGS. 15A and
15B, in these cryogenic ablation device designs, a cryogenic fluid,
such as a pressurized gas (like Freon for example) is passed through
an inflow lumen 90 in the ablation device transmission line 72.
The distal ablative device 26 is preferably provided by a decompression
chamber which decompresses the pressurized gas from the inflow lumen
90 therein. Upon decompression or expansion of the pressurized gas
in the decompression chamber 91, the temperature of the exterior
surface 92 of the decompression chamber is sufficiently reduced
to cause tissue ablation upon contact thereof. The decompressed
gas is then exhausted through the outflow lumen 93 of the transmission
line 72.
FIG. 15B illustrates that the directive component 73 is in the
form of a thermal insulation layer extending longitudinally along
one side of the energy delivery portion 27. By forming a good thermal
insulator with a low thermal conductivity, the C-shaped insulation
layer 73 will substantially minimize undesirable cryogenic ablation
of the immediate tissue surrounding of the targeted tissue region.
In one configuration, the isolation layer may define a thin, elongated
gap 95 which partially surrounds the decompression chamber 91. This
gap 95 may then be filled with air, or an inert gas, such as CO.sub.2,
to facilitate thermal isolation. The isolation gap 95 may also be
filled with a powder material having relatively small solid particulates
or by air expended polymer. These materials would allow small air
gaps between the insulative particles or polymeric matrix for additional
insulation thereof. The isolation layer may also be provided by
a refractory material. Such materials forming an insulative barrier
include ceramics, oxides, etc.
Referring now to FIG. 16, an ultrasound ablation device may also
be applied as another viable source of ablation energy. For example,
a piezoelectric transducer 96 may be supplied as the ablative element
which delivers acoustic waves sufficient to ablate tissue. These
devices emit ablative energy which can be directed and shaped by
applying a directive echogenic component to reflect the acoustic
energy. Moreover, a series or array of piezoelectric transducers
96, 96' and 96'' can be applied to collectively form a desired radiation
pattern for tissue ablation. For example, by adjusting the delay
between the electrical exciting signal of one transducer and its
neighbor, the direction of transmission can be modified. Typical
of these transducers include piezoelectric materials like quartz,
barium oxides, etc.
In this configuration, the directive component 73 of the ultrasonic
ablation device may be provided by an echogenic material (73-73')
positioned proximate the piezoelectric transducers. This material
reflects the acoustic wave and which cooperates with the transducers
to direct the ablative energy toward the targeted tissue region.
By way of example, such echogenic materials are habitually hard.
They include, but are not restricted to metals and ceramics for
example.
Moreover, when the ablative energy is ultrasonic based, it will
be appreciated that it is desirable that both the ablation sheath
22 and the ablation device be composed of materials which have low
absorption of the acoustic waves, and that provide a good acoustic
impedance matching between the tissue and the transducer. In that
way, the thickness and the material chosen for the ablation sheath
play in important role to match the acoustic properties of the tissue
to be ablated and the transducer. An impedance matching jelly can
also be used in the ablation sheath to improve the acoustic impedance
matching.
Lastly, the ablation device may be provided by a radiofrequency
(RF) ablation source which apply RF conduction current sufficient
to ablate tissue. These conventional ablation instruments generally
apply conduction current in the range of about 450 kHz to about
550 kHz. Typical of these RF ablation devices include ring electrodes,
coiled electrodes or saline electrodes.
To selectively direct the RF energy, the directive component is
preferably composed of an electrically insulative and flexible material,
such as plastic or silicone. These biocompatible materials perform
the function of directing the conduction current toward a predetermined
direction.
In an alternative embodiment, as best viewed in FIG. 17, the window
portion 58 of the ablation sheath 22 is provided by an opening in
the sheath along the ablation path, as opposed to being merely transparent
to the energy ablation devices. In this manner, when the ablation
sheath 22 is properly positioned with the window portion placed
proximate and adjacent the targeted tissue, the energy delivery
portion 27 of the ablation device 26 may be slidably positioned
into direct contact with the tissue for ablation thereof. Such direct
contact is especially beneficial when it is technically difficult
to find a sheath that is merely transparent to the used ablative
energy. For example, it would be easier to use a window portion
when RF energy is used. The ablative RF element could directly touch
the tissue to be ablated while the directive element would be the
part of the ablation sheath 22 facing away the window portion 58.
Furthermore, during surgical ablation, the window portion could
be used by the surgeon to indicate the area where an ablation can
potentially be done with the energy ablation device.
In yet another embodiment, the ablation system 20 may be in the
form of a rail system including a rail device 96 upon which the
ablation device 26 slides therealong as compared to therethrough.
FIGS. 18 and 19 illustrate the rail device 96 which is preferably
pre-shaped or bendable to proximately conform to the surface of
the targeted tissue. Once the rail device 96 is positioned, the
ablation device can be advanced or retracted along the path defined
by the rail device for ablation of the targeted tissue 21.
The ablation device 26 in this arrangement includes a body portion
98 housing the energy delivery portion 27 therein. The window portion
58 is preferably extend longitudinally along the outer surface of
one side of the housing. An opposite side of the housing, and longitudinally
oriented substantially parallel to the window portion 58 is a rail
receiving passage 97 formed and dimensioned to slidably receive
and slide over the rail device 96 longitudinally therethrough. In
one configuration, the energy delivery portion 27 may be advanced
by pushing the body portion 98 through the transmission line 72.
Alternatively, the energy delivery portion 27 may be advanced by
pulling the body portion 98 along the path of the rail system 20.
As best viewed in FIG. 19, the directive component 73 of the ablation
device 26 is integrally formed with the body portion 98 of the ablation
device. This preferably C-shaped component extends partially peripherally
around the energy delivery portion 27 to shield the rail device
96 from exposure to the ablative energy. Depending upon the type
of ablative energy employed, the material or structure of the directive
component 73 can be constructed as set forth above.
To assure the directional position and orientation of the window
portion 58 of the ablative device toward the targeted tissue, a
key structure 48 is employed. Generally, the transverse cross-sectional
dimension of the rail device 96 and matching rail receiving passage
97 is shaped to assure proper directional orientation of the ablative
energy. Examples of such key forms are shown in FIGS. 20A-20B.
As with the previous embodiments, the open window embodiment and
the rail system embodiment may employ multiple ablative element
technology. These include microwave, radiofrequency, laser, ultrasound
and cryogenic energy sources.
In accordance with another aspect of the present invention, the
tissue ablation system further includes a temperature sensor which
is applied to measure the temperature of the ablated tissue during
the ablation. In one embodiment, the temperature sensor is mounted
to the ablation device proximate the energy delivery portion 27
so that the sensor moves together with the energy delivery portion
as it is advanced through the ablation sheath. In another embodiment,
the temperature sensor is attached on the ablation sheath.
To determine the temperature of the ablated tissue, a mathematical
relationship is used to calculate the tissue temperature from the
measured temperature. Typical of such temperature sensors include
a metallic temperature sensor, a thermocouple, a thermistor, or
a non-metallic temperature sensor such as fiber optic temperature
sensor.
In accordance with the present invention, the guide sheath 52 and
the ablation sheath 22 can be designed and configured to steer the
ablative device along any three dimensional path. Thus, the tissue
ablation system of present invention may be adapted for an abundance
of uses. For instance, the distal end portion of the ablation sheath
can be configured to form a closed ablation path for the ablation
device. This design may be employed to ablate around an ostium of
an organ, or to electrically isolate one or several pulmonary veins
to treat atrial fibrillation. A closed ablation path may also utilized
to ablate around an aneurysm, such as a cardiac aneurysm or tumor,
or any kink of tumor. In other example, the ablation sheath can
be inserted in an organ in order to ablate a deep tumor or to perform
any surgical treatment where a tissue ablation is required.
In other instances, the distal end portion of the ablation sheath
22 may define a rectilinear or curvilinear open ablation path for
the ablation device. Such open ablation paths may be applied to
ablate on the isthmus between the inferior vena cava vein (IVC)
and the tricuspid valve (TV), to treat regular flutter, or to generate
a lesion between the IVC and the SVC, to avoid macro-reentry circuits
in the right atrium. Other similar ablation lesions can be formed
between: any of the pulmonary vein ostium to treat atrial fibrillation;
the mitral valve and one of the pulmonary veins to avoid macro-reentry
circuit around the pulmonary veins in the left atrium; and the left
appendage and one of the pulmonary veins to avoid macro-reentry
circuit around the pulmonary veins in the left atrium.
The ablation apparatus may be applied through several techniques.
By way of example, the ablation apparatus may be inserted into the
coronary circulation to produce strategic lesions along the endocardium
of the cardiac chambers (i.e., the left atrium, the right atrium,
the left ventricle or the right ventricle). Alternatively, the ablation
apparatus may be inserted through the chest to produce epicardial
lesions on the heart. This insertion may be performed through open
surgery techniques, such as by a sternotomy or a thoracotomy, or
through minimally invasive techniques, applying a cannula and an
endoscope to visualize the location of the ablation apparatus during
a surgery.
The ablation apparatus is also suitable for open surgery applications
such as ablating the exterior surfaces of an organ as well, such
as the heart, brain, stomach, esophagus, intestine, uterus, liver,
pancreas, spleen, kidney or prostate. The present invention may
also be applied to ablate the inside wall of hollow organs, such
as heart, stomach, esophagus, intestine, uterus, bladder or vagina.
When the hollow organ contains bodily fluid, the penetration port
formed in the organ by the ablation device must be sealed to avoid
a substantial loss of this fluid. By way of example, the seal may
be formed by a purse string, a biocompatible glue or by other conventional
sealing devices.
As mentioned, the present invention may be applied in an intra-coronary
configuration where the ablation device is used to isolate the pulmonary
vein from the left atrium. FIG. 2C illustrates that a distal end
of the ablation sheath 22 is adapted for insertion into the pulmonary
vein. In this embodiment, the distal end of the ablation device
may include at least one electrode used to assess the electrical
isolation of the vein. This is performed by pacing the distal electrode
to "capture" the heart. If pacing captures the heart,
the vein is not yet electrically isolated, while, if the heart cannot
be captured, the pulmonary vein is electrically isolated from the
left atrium. As an example, a closed annular ablation on the posterior
wall of the left atrium around the ostium of the pulmonary vein
by applying the pigtail ablation sheath 22 of FIGS. 2 and 4.
In yet another configuration, the ablation device may include a
lumen to inject a contrasting agent into the organ. For instance,
the contrasting agent facilitates visualization of the pulmonary
vein anatomy with a regular angiogram technique. This is important
for an intra-coronary procedure since fluoroscopy is used in this
technique. The premise, of course, is to visualize the shape and
the distal extremity of the sheaths, as well as the proximal and
distal part of the sliding energy delivery portion during an ablative
procedure under fluoroscopy. It is essential for the electrophysiologist
to be able to identify not only the ablative element but also the
path that the ablation sheath will provide to guide the energy delivery
portion 27 therealong.
Another visualization technique may be to employ a plurality of
radio-opaque markers spaced-apart along the guide sheath to facilitate
location and the shape thereof. By applying the radio-opaque element
that will show the shape of the sheath. This element can be a metallic
ring or soldering such as platinum which is biocompatible and very
radio-opaque. Another example of a radio-opaque element would be
the application of a radio-opaque polymer such as a beryllium loaded
material. Similarly, radio-opaque markers may be disposed along
the proximal, middle and distal ends of the energy delivery portion
27 to facilitate the visualization and the location of the energy
delivery portion when the procedure is performed under fluoroscopy.
To facilitate identification of the distal end portion of the ablation
sheath, a fluoro-opaque element may be placed at the distal extremity.
Another implementation of this concept would be to have different
opacities for the ablation sheath and the energy delivery portion
27. For example, the energy delivery portion may be more opaque
than that of the ablation sheath, and the ablation sheath may be
more opaque than the trans-septal sheath, when the later is used.
The surgical ablation device of the present invention may also
be applied minimally invasively to ablate the epicardium of a beating
heart through an endoscopic procedure. As viewed in FIGS. 21 and
22, at least one intercostal port 85 or access port is formed in
the thorax. A dissection tool (not shown) or the like may be utilized
to facilitate access to the pericardial cavity. For instance, the
pericardium may be dissected to enable access to the epicardium
of a beating heart. The pericardial reflections may be dissected
in order to allow the positioning of the ablation device 26 around
the pulmonary veins. Another dissection and positioning tool 100,
described in more detail below, may also be utilized to puncture
the pericardial reflection located in proximity to a pulmonary vein
and assist in positioning the ablation device housed therein. After
the puncture of the pericardial reflection, the ablation sheath
can be positioned around one, or more than one pulmonary vein in
order to produce the ablation pattern used to treat the arrhythmia,
atrial fibrillation in particular.
For example, a guide sheath 52 may be inserted through the access
port 85 while visualizing the insertion process with an endoscopic
device 86 positioned in another access port 87. Once the guide sheath
52 is properly positioned by handle 88, the ablation sheath 22 may
be inserted through the guide sheath, while again visualizing the
insertion process with the endoscopic system to position the ablation
sheath on the targeted tissue to ablate. The ablation device may
then be slid through the ablation lumen of the ablation sheath and
adjacent the targeted tissue. Similar to the previous ablation techniques,
the ablative element of the ablation device may be operated and
negotiated in an overlapping manner to form a gap free lesion or
a plurality of independent lesions. The ablation sheath may also
be malleable or flexible. The surgeon can use a surgical instrument,
like a forceps, to manipulate, bend and position the ablation sheath.
With reference also made to FIGS. 23A-C, a dissection and positioning
tool 100 will now be described, in accordance with the present invention.
As stated above, the dissection and positioning tool 100 allows
a surgeon to gain access to, and further position medical instruments,
such as the ablation system described herein, at various surgical
sites throughout the body, especially during minimally invasive
surgical procedures on the beating heart. More specifically, tool
100 further enables a surgeon to place the ablation device of an
ablation instrument, or other medical instrument, adjacent to the
outer surfaces of bodily structures along a predetermined lesion
path, surrounding the structure for example. For illustration purposes
only, the positioning tool 100 provides better access to the pulmonary
truck and, more specifically, the individual pulmonary veins, during
minimally invasive procedures facilitating placement of an ablation
device adjacent to one or more pulmonary veins.
As shown in FIGS. 23A and 23B, positioning tool 100 comprises a
handle 102 and a guide sheath 104 having a deflectable tip 106 operably
attached to the distal end of sheath 104. Guide sheath 104 and tip
106 may be made from any suitable biocompatible material, such as
those materials described herein with respect to sheath 52.
As will become readily apparent, |