U.S. patent application number 12/946735 was filed with the patent office on 2011-05-19 for cardiac ablation devices.
This patent application is currently assigned to Recor Medical, Inc.. Invention is credited to Todd Fjield, John Hotmer, Patrick David Lopath, Jaime Merino, Robert C. Pacheco, James Savage, Yegor Sinelnikov, Reinhard Warnking, Yong Zou.
Application Number | 20110118632 12/946735 |
Document ID | / |
Family ID | 32908655 |
Filed Date | 2011-05-19 |
United States Patent
Application |
20110118632 |
Kind Code |
A1 |
Sinelnikov; Yegor ; et
al. |
May 19, 2011 |
CARDIAC ABLATION DEVICES
Abstract
A cardiac ablation device treats atrial fibrillation by
directing and focusing ultrasonic waves into a ring-like ablation
region (A). The device desirably is steerable and can be moved
between a normal disposition, in which the ablation region lies
parallel to the wall of the heart for ablating a loop-like lesion,
and a canted disposition, in which the ring-like focal region is
tilted relative to the wall of the heart, to ablate only a short,
substantially linear lesion. The ablation device desirably includes
a balloon reflector structure (18, 1310) and an ultrasonic emitter
assembly (23, 1326), and can be steered and positioned without
reference to engagement between the device and the pulmonary vein
or ostium. A contrast medium (C) can be injected through the
ablation device to facilitate imaging, so that the device can be
positioned based on observation of the images.
Inventors: |
Sinelnikov; Yegor; (Port
Jefferson, NY) ; Zou; Yong; (S. Setauket, NY)
; Warnking; Reinhard; (Setauket, NY) ; Savage;
James; (Farmingville, NY) ; Pacheco; Robert C.;
(Commack, NY) ; Merino; Jaime; (Elmont, NY)
; Lopath; Patrick David; (Durham, NC) ; Hotmer;
John; (Sound Beach, NY) ; Fjield; Todd;
(Laguna Hills, CA) |
Assignee: |
Recor Medical, Inc.
|
Family ID: |
32908655 |
Appl. No.: |
12/946735 |
Filed: |
November 15, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10783310 |
Feb 20, 2004 |
7837676 |
|
|
12946735 |
|
|
|
|
60448804 |
Feb 20, 2003 |
|
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Current U.S.
Class: |
601/2 |
Current CPC
Class: |
A61B 2017/22061
20130101; A61B 2017/22027 20130101; A61B 17/2251 20130101; A61B
2017/00243 20130101; A61B 17/2202 20130101; A61B 2017/00991
20130101; A61B 17/22004 20130101; A61B 2017/22054 20130101; A61B
17/22012 20130101 |
Class at
Publication: |
601/2 |
International
Class: |
A61N 7/00 20060101
A61N007/00 |
Claims
1-82. (canceled)
83. An apparatus for applying ultrasonic energy to cardiac tissue,
the apparatus comprising: a catheter; an ultrasonic transducer
disposed on the catheter, the ultrasonic transducer configured to
emit ultrasonic energy; and a plurality of expandable structures
disposed around a circumference of the catheter, the expandable
structures configured to contact an anatomical structure when
expanded to position the ultrasonic transducer relative to the
cardiac tissue, wherein each of the expandable structures is
independently expandable.
84. The apparatus of claim 83, wherein the plurality of expandable
structures are arranged around the circumference of the catheter
when expanded.
85. The apparatus of claim 83, wherein the plurality of expandable
structures are arranged around the ultrasonic transducer when
expanded.
86. The apparatus of claim 83, wherein the expandable structures
comprise balloons.
87. The apparatus of claim 86, wherein the catheter further
comprises a plurality of lumens extending from a proximal end of
the catheter to corresponding balloons.
88. The apparatus of claim 87, wherein each balloon is configured
to be independently expanded by introducing an aqueous liquid to
the balloon through the corresponding lumen.
89. The apparatus of claim 88, wherein the aqueous liquid comprises
a contrast medium.
90. The apparatus of claim 87, wherein each balloon is configured
to be independently expanded by introducing a gas to the balloon
through the corresponding lumen.
91. The apparatus of claim 83, wherein at least one of the
plurality of expansible structures is configured to reflect
ultrasonic energy emitted from the ultrasonic transducer when
expanded.
92. The apparatus of claim 83, wherein at least one of the
plurality of expansible structures is configured to be
non-reflective to ultrasonic energy emitted from the ultrasonic
transducer when expanded.
93. The apparatus of claim 83, wherein the catheter further
comprises a guidewire lumen.
94. A method for applying ultrasonic energy to cardiac tissue, the
method comprising: advancing a catheter adjacent to the cardiac
tissue, the catheter having an ultrasonic transducer and a
plurality of expandable structures disposed around a circumference
of the catheter; expanding a first expandable structure of the
plurality of expandable structures such that the first expandable
structure contacts an anatomical structure to position the
ultrasonic transducer relative to the cardiac tissue, wherein each
of the expandable structures is independently expandable.
95. The method of claim 94, further comprising expanding a second
expandable structure of the plurality of expandable structures such
that the second expandable structure contacts an anatomical
structure to position the ultrasonic transducer relative to the
cardiac tissue.
96. The method of claim 95, wherein the catheter further comprises
a first lumen extending from a proximal end of the catheter to the
first expandable structure and a second lumen extending from the
proximal end of the catheter to the second expandable structure,
wherein expanding the first expandable structure comprises
introducing a fluid to the first expandable structure through the
first lumen, and wherein expanding the second expandable structure
comprises introducing a fluid to the second expandable structure
through the second lumen.
97. The method of claim 94, further comprising emitting ultrasonic
energy from the ultrasonic transducer to cause shrinkage of the
cardiac tissue.
98. The method of claim 97, further comprising reflecting the
ultrasonic energy emitted from the ultrasonic transducer using the
expanded first expandable structure.
99. The method of claim 94, wherein the plurality of expandable
structures are arranged around the circumference of the catheter
when expanded.
100. The method of claim 94, wherein the plurality of expandable
structures are arranged around the ultrasonic transducer when
expanded.
101. The method of claim 94, wherein the first expandable
structures comprises a balloon, the expanding comprising inflating
the balloon with an aqueous liquid.
102. The method of claim 101, further comprising deflating the
balloon and removing the apparatus from a human.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of U.S. patent
application Ser. No. 10/783,310, filed Feb. 20, 2004, now U.S. Pat.
No. 7,837,676, which claims benefit of U.S. Provisional Patent
Application Ser. No. 60/448,804, filed Feb. 20, 2003, the entire
contents of both of which are hereby incorporated by reference
herein.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to ablation apparatus and
methods and to steerable devices, including those used in cardiac
ablation
[0003] Contraction or "beating" of the heart is controlled by
electrical impulses generated at nodes within the heart and
transmitted along conductive pathways extending within the wall of
the heart. Certain diseases of the heart known as cardiac
arrhythmias involve abnormal generation or conduction of the
electrical impulses. One such arrhythmia is atrial fibrillation or
"AF." Certain cardiac arrhythmias can be treated by deliberately
damaging the tissue along a path crossing a route of abnormal
conduction, either by surgically cutting the tissue or applying
energy or chemicals to the tissue, so as to form scar. The scar
blocks the abnormal conduction. For example, in treatment of AF it
has been proposed to ablate tissue in a partial or complete loop
around a pulmonary vein within the vein itself near the ostium of
the vein; within the ostium; or within the wall of the heart
surrounding the ostium. It would be desirable to perform such
ablation using a catheter-based device which can be advanced into
the heart through the patient's circulatory system.
[0004] As described in co-pending, commonly assigned U.S. patent
application Ser. No. 09/905,227, published as US/2002/0065512-A1
(the "'512 publication") and granted as U.S. Pat. No. 6,635,054,
the disclosures of which are hereby incorporated by reference
herein, an expansible structure is used as a reflector for
directing and focusing ultrasonic waves from an ultrasonic
transducer into a region of tissue to be ablated. As further
described in the '512 publication, certain preferred embodiments
according to that disclosure include an expansible structure
incorporating a structural balloon which is inflated with a liquid
and a reflector balloon inflated with a gas. The balloons share a
common wall. The balloons are configured so that the common wall
has a generally parabolic shape. Because the liquid in the
structural balloon and the gas in the reflector balloon have
substantially different acoustic impedances, the interface between
the balloons at the common wall is a nearly perfect reflector for
ultrasonic waves. Ultrasonic waves are emitted from a small
transducer within the structural balloon and passes radially
outwardly from the emitter to the reflector. The reflector
redirects the ultrasonic waves and focuses it into a ring-like
ablation region encircling the central axis of the emitter and
balloons. This ablation region is just forward of the structural
balloon. Thus, the ultrasonic waves will ablate tissue in a region
encircling the central axis or forward-to-rearward axis of the
balloon structure.
[0005] This arrangement can be used, for example, to treat atrial
fibrillation by ablating a circular region of myocardial tissue
encircling the ostium of a pulmonary vein. The ablated tissue forms
a barrier to abnormal electrical impulses which can be transmitted
along the pulmonary veins and, thus, isolates the myocardial tissue
of the atrium from the abnormal impulses. To provide effective
treatment in this mode of operation, the ring-like focal region
should encircle the ostium and should lie in a plane which is
parallel or nearly parallel with the inner surface of the heart. In
some embodiments disclosed in the '512 publication, the structural
balloon is provided with a forwardly projecting tip at its central
or forward-to-rearward axis, so that by engaging the tip in the
lumen of the pulmonary vein, the forward-to-rearward axis of the
balloon structure can be placed at the center of the ostium. A
guide wire can be threaded into the pulmonary vein. The balloon is
then advanced along the guide wire until the tip lodges in the
ostium in the pulmonary vein. Where the particular pulmonary vein
being treated has a main trunk which extends generally
perpendicular to the interior surface of the heart wall, and where
the ostium has the expected configuration, this arrangement works
properly.
[0006] However, there is significant variability in the anatomy of
the pulmonary veins and their ostia. For example, that portion of
the pulmonary vein adjacent the ostium may lie at an oblique angle
to the interior surface of the heart wall. In order to engage the
tip of the structural balloon in such an ostium, the
forward-to-rearward axis of the balloon must be tilted at a
comparable angle, so that the ablation region is unintentionally
tilted relative to the interior surface of the heart wall. Also,
two or more pulmonary veins may join one another close to a common
opening or ostium or may be enlarged or shaped so that it is
difficult to engage the tip in the ostium. Moreover, even where the
patient has the desired, nominal anatomy, it has been difficult to
confirm proper placement of the balloon assembly. Thus, still
further improvements would be desirable.
[0007] The delicate tissues within the pulmonary vein can be
damaged by forcibly engaging structures with these tissues and by
moving the engaged structures while the structures are forcibly
engaged with the tissues. It would be desirable to provide an
improved system and method which does not rely on such forcible
engagement to orient the balloon or other ablation device in the
desired disposition. Further, it is often necessary or desirable to
move an ablation device to several different dispositions within
the heart chamber. For example, the treatment plan may require
formation of loop-like lesions around the individual ostium of each
of several pulmonary veins. It would be desirable to provide
apparatus and methods which facilitate such repositioning.
[0008] Further, it has been proposed that more effective treatment
can be provided by ablated generally linear lesions along the heart
wall in conjunction with loop-like lesions. However, heretofore it
has been proposed to form the linear lesions using specialized
devices as, for example, catheters equipped with a point energy
source such as a single pair of electrodes for applying RF energy,
so that the linear lesion can be traced by moving the catheter so
as to move the single point source along the heart wall or,
alternatively, by catheters equipped with numerous energy emitters
such as numerous RF electrodes disposed along the length of the
catheter. Such a catheter may be provided as a separate device
which must be separately introduced into the heart, thus
complicating and prolonging the procedure. Alternatively, it has
been proposed to provide such a catheter as a portion of a catheter
carrying a device for forming a loop-like lesion. Although this
approach theoretically simplifies the task of positioning the
needed devices within the heart, in fact, it substantially
complicates the construction of the device and also complicates the
tasks of positioning each individual device. Thus, further
improvement in this regard would also be desirable.
[0009] Moreover, further improvements in construction of expansible
ablation devices, including balloon-based ablation devices, would
be helpful. In particular, it would be desirable to provide
improved structures which facilitate cooling of a piezoelectric
ultrasonic emitter, and structures which can reinforce the
expansible device when the same is in an expanded condition. It
would also be desirable to provide a back-up system which would
minimize the consequences in the unlikely event of a structural
failure in one or more components of the device. It would be
desirable to provide these improvements without substantially
increasing the diameter of the expansible ablation device when the
same is in a collapsed condition.
SUMMARY OF THE INVENTION
[0010] The various aspects of the present invention address these
needs.
[0011] One aspect of the present invention provides apparatus for
performing cardiac ablation in a mammalian subject. Apparatus
according to this aspect of the invention includes an insertable
structure which incorporates a catheter having proximal and distal
ends, as well as an ablation device mounted to the catheter
adjacent the distal end thereof. The ablation device is adapted for
placement within a chamber of the heart of the subject and is
adapted to ablate a region of the cardiac structure bounding the
chamber when the ablation device is in an operative configuration.
The insertable structure also defines an outlet port open to a
distal side of the ablation device, i.e., that side of the ablation
device furthest from the proximal end, and further defines a
continuous passageway extending from adjacent the proximal end of
the catheter. Most preferably, the apparatus according to this
aspect of the invention further includes a source of a contrast
medium adapted for connection to the passageway adjacent the
proximal end of the catheter. The source of contrast medium is
operative to pass contrast medium through the passageway and into
the subject through the outlet port while the ablation device is in
its operative condition.
[0012] Most preferably, the ablation device includes an expansible
structure which may be, for example, a balloon structure as
discussed above. The expansible structure has a collapsed,
inoperative state and an expanded state. The ablation device is in
the operative condition when the expansible structure is in its
expanded state.
[0013] A method according to a related aspect of the invention
includes the step of providing an ablation device in a chamber of
the heart of a mammalian subject, such that the device is in an
operative configuration with a distal side of the device facing
toward a region of the cardiac structure to be ablated, and, while
the ablation device is in its operative configuration, injecting a
contrast medium into the chamber on the distal side of the ablation
device. The method most desirably further includes obtaining one or
more images depicting the contrast medium in at least a portion of
the cardiac structure as, for example, by x-ray or fluoroscopic
imaging. Methods according to this aspect of the invention allow
the physician to confirm placement of the device while the device
is in its operative condition as, for example, while a balloon or
other expansible structure is in its expanded state. Most
preferably, the methods according to this aspect of the invention
are performed without introducing a separate catheter to carry the
contrast medium, as by using the continuous passageway discussed
above in connection with the apparatus. The methods according to
this aspect of the invention may further include the step of
adjusting the position of the ablation device, based in part or
entirely on the relationship between the ablation device and the
cardiac structure observed in the imaging step. These methods allow
the physician to position the device during the procedure, without
relying on a predetermined mechanical relationship between the
device and the cardiac structure.
[0014] Apparatus according to a further embodiment of the invention
includes a catheter and an ultrasonic device having a
forward-to-rearward axis. The ultrasonic device is arranged to emit
ultrasonic waves so that the emitted ultrasonic waves are directed
into at least a portion of a ring-like region surrounding the
forward-to-rearward axis. The ablation device is mounted to the
catheter. Apparatus according to this aspect of the invention
includes a steering system adapted to selectively vary the
disposition of the ablation device and, in particular, the
disposition of the forward-to-rearward axis of the ablation device
relative to the heart of the subject, while the ultrasonic ablation
device is disposed in a chamber of the heart of the subject. Here
again, the ultrasonic ablation device most preferably includes an
expansible structure such as a balloon structure having a
collapsed, inoperative state and an expanded state. The steering
system preferably is operative to selectively vary the disposition
of the ablation device while the expansible structure is in its
expanded state as, for example, while a balloon-based expanded
structure is in an inflated condition. Most preferably, the
steering system is arranged to selectively vary the disposition of
the ultrasonic ablation device independently of engagement between
the cardiac structure and any element of the apparatus distal to
the ultrasonic ablation device. Most preferably, the catheter has a
bendable section located proximally or rearwardly of the forward
end of the ablation device, and the steering system is arranged to
selectively bend this bendable section of the catheter under the
control of the physician. In a particularly preferred arrangement,
the expansible structure includes an internal reinforcing structure
having a distal end linked to the expansible structure adjacent the
forward end of the expansible structure, and having a proximal end
mechanically linked to the expansible structure adjacent the
rearward end thereof. The reinforcing structure may include an
ultrasonic emitter assembly, as well as an extensible structure.
Preferably, the reinforcing structure becomes relatively flexible
when the expansible structure is in a collapsed condition and
becomes more rigid when the expansible structure is in its expanded
condition. As further discussed below, this arrangement allows the
reinforcing structure to maintain the shape of the expansible
structure in its expanded or inflated condition, but facilitates
threading of the device through the body to the heart.
[0015] The steering system most desirably includes at least one
pull wire mechanically connected to the reinforcing structure,
typically adjacent the proximal end thereof. As further discussed
below, steering by pulling on the internal reinforcing structure
within the expansible structure tends to bend the catheter in such
a way that the expansible structure turns about a pivot axis
relatively close to the forward end of the expansible structure.
This makes it easier to maneuver the expanded structure within the
confines of a heart chamber.
[0016] A method of cardiac ablation according to a related aspect
of the present invention includes the steps of advancing apparatus
including a catheter bearing an ultrasonic ablation device into the
subject until the ultrasonic ablation device is within a chamber of
the heart and positioning the ultrasonic ablation device in a first
disposition within the chamber by selectively varying the
disposition of the forward-to-rearward axis of the ultrasonic
ablation device relative to the catheter, and then while the
ultrasonic ablation device is in this first disposition, ablating
the heart wall to form a first lesion by actuating the ablation
device to direct ultrasonic waves into at least a portion of a
ring-like region surrounding the forward-to-rearward axis of the
device. The method also includes the step of removing the
ultrasonic ablation device from the subject. Most preferably, the
method further includes the step of repositioning the ultrasonic
ablation device from the first disposition to a different, second
disposition within the chamber by further selectively varying the
disposition of the forward-to-rearward axis relative to the
catheter, and, while the device is in the second disposition,
ablating the heart wall to form a second lesion, again by actuating
the ablation device to direct ultrasonic waves into the ring-like
region. Most desirably, the repositioning and additional ablation
steps are performed prior to removal of the device. The device
remains within the chamber, and most preferably remains in an
expanded, operative condition, while it is repositioned. Additional
repositioning and actuating steps may be employed as well, so as to
form further lesions.
[0017] Desirably, at least one of the dispositions of the ablation
device is a so-called "normal" disposition in which the
forward-to-rearward axis of the device lies approximately
perpendicular to a wall of the heart with at least a major portion
of the ring-like ablation region disposed within or in close
proximity to the wall of the heart. Ablation in this disposition
forms a lesion in the form of at least a substantial portion of a
loop. Alternatively or additionally, at least one of the
dispositions may be a canted disposition in which the
forward-to-rearward axis of the device lies at a substantially
non-perpendicular angle to the wall of the heart, so that only a
minor portion of the ring-like region is disposed within or in
close proximity to the wall of the heart. Ablation in this
disposition forms a lesion in the form of only a small portion of a
loop, approximating a linear lesion. Thus, the same tool can be
used to form both loop-like lesions and substantially linear
lesions. Most desirably, the ablation device is arranged to focus
the ultrasonic waves into the ring-like ablation region, so that
the ultrasonic waves have intensity which increases in the
direction of propagation of the energy from the device to the
ablation region and decreases in the same direction, beyond the
ablation region. Typically, the ultrasonic waves are directed
indiscriminately into the entire ablation region. In the normal
disposition, all or almost all of this energy performs the
desirable function of ablating the loop-like lesion. However, in
the canted disposition, only a portion of the ablation region is
disposed where ablation is desired. Other portions of the ablation
region typically are disposed remote from a heart wall to be
ablated. However, ultrasonic waves directed into those remote
portions of the ablation region will pass through the ablation
region and will dissipate, typically without damaging other
structures.
[0018] Yet another aspect of the invention provides an ultrasonic
ablation device including an ultrasonic emitter assembly which has
proximal and distal ends. The emitter assembly includes a tubular
piezoelectric element having proximal and distal ends and a tube,
referred to herein as the "inside tube," extending within the
tubular piezoelectric element, so that the inside tube and the
piezoelectric element cooperatively define an annular passageway
extending between the proximal and distal ends of the piezoelectric
element. The apparatus desirably further includes a balloon having
an interior space. The annular passageway inside the piezoelectric
element communicates with the interior of the balloon adjacent the
distal end of the emitter assembly. The apparatus most preferably
further includes a catheter having proximal and distal ends. The
catheter has a first lumen, referred to herein as a principal
lumen, most typically disposed adjacent the center of the catheter,
and also has first and second additional lumens. The principal
lumen communicates with the bore of the inside tube. The first
additional lumen communicates with the proximal end of the annular
passageway, and the second additional lumen communicates with the
interior of the balloon adjacent the proximal end of the emitter
assembly. The emitter assembly may include a proximal mounting
structure disposed at least partially between the distal end of the
catheter and the proximal end of the tubular piezoelectric element.
The proximal mounting structure desirably defines a first channel
which connects the first additional lumen of the catheter with the
annular passageway, a second channel communicating with the second
additional lumen of the catheter and a port communicating with the
second channel and with the interior of the balloon, so that the
second additional lumen communicates with the interior of the
balloon through the port.
[0019] In the preferred apparatus according to this aspect of the
invention, the piezoelectric element can be cooled by directing
liquid through the first additional lumen of the catheter and
through the annular channel inside the piezoelectric element. The
liquid passes from the annular channel into the interior of the
balloon, passes through the interior of the balloon back through
the port and into the second additional lumen of the catheter. The
principal lumen of the catheter and the bore of the inside tube
desirably define a portion of the continuous passageway discussed
above. Because the principal lumen is not employed in circulation
of the cooling liquid, it remains free for purposes such as
introduction of a contrast medium. The emitter assembly may also
include a distal mounting element mounted to the distal end of the
piezoelectric element. The mounting elements may be electrically
conductive and may serve as electrical pathways to the
piezoelectric element. Moreover, a pull wire may be connected to
one of the mounting structures, typically to the proximal mounting
structure, so as to provide the desired bending action as discussed
above. The apparatus may further include an extensible element. As
further discussed below, the extensible reinforcing element may
include elements which cooperate with the distal mounting
structure.
[0020] Still other aspects of the invention provide alternative
structures and methods.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a diagrammatic view depicting a catheter and
ablation device in accordance with one embodiment of the invention,
in conjunction with certain features of a heart.
[0022] FIG. 2 is a view similar to FIG. 1 depicting apparatus in
accordance with another embodiment of the invention.
[0023] FIG. 3 is a diagrammatic sectional view depicting a portion
of a catheter according to one embodiment of the invention.
[0024] FIG. 4 is a sectional view taken along line 3-3 in FIG.
3.
[0025] FIG. 5 is a fragmentary, diagrammatic elevational view
depicting a portion of an apparatus according to yet another
embodiment of the present invention.
[0026] FIG. 6 is a fragmentary sectional view depicting a portion
of apparatus according to a further embodiment of the
invention.
[0027] FIG. 7 is a view similar to FIG. 6, but depicting apparatus
according to another embodiment of the invention.
[0028] FIG. 8 is a fragmentary sectional view depicting apparatus
according to a still further embodiment of the invention.
[0029] FIG. 9 is a view similar to FIG. 8 depicting the apparatus
of FIG. 8 in another operating condition.
[0030] FIGS. 10 and 11 are views similar to FIG. 9, but depicting
apparatus according to yet another embodiment of the invention in
two operating conditions.
[0031] FIG. 12 is a diagrammatic sectional view depicting a portion
of apparatus according to yet another embodiment of the
invention.
[0032] FIG. 13 is a fragmentary elevational view depicting
apparatus according to a still further embodiment of the
invention.
[0033] FIG. 14 is a diagrammatic, partially perspective view
depicting apparatus according to another embodiment of the
invention.
[0034] FIGS. 15 and 16 are perspective views depicting a structure
used in the embodiment of FIG. 14.
[0035] FIGS. 17 and 18 are perspective views depicting another
structure used in the embodiment of FIGS. 14-16.
[0036] FIG. 19 is a fragmentary perspective view showing a portion
of the structure depicted in FIG. 14.
[0037] FIG. 20 is a sectional view taking along line 20-20 in FIG.
14.
[0038] FIG. 21 is a fragmentary perspective view depicting a
portion of the structure shown in FIGS. 14-20.
[0039] FIG. 22 is a diagrammatic sectional view depicting a portion
of the structure shown in FIGS. 14-21 in a collapsed condition.
[0040] FIG. 22A is a fragmentary view on an enlarged scale of the
area indicated in FIG. 22.
[0041] FIG. 23 is a view similar to FIG. 22, but depicting the same
portion of the structure in an expanded condition.
[0042] FIG. 24 is a schematic view depicting certain geometrical
relationships between the structures of FIGS. 14-23 and a portion
of the heart wall during a method in accordance with one embodiment
of the invention.
[0043] FIGS. 25 and 26 are views similar to FIGS. 22 and 23, but
depicting apparatus according to yet another embodiment of the
invention.
[0044] FIG. 27 is a schematic elevational view depicting apparatus
according to yet another embodiment of the invention.
[0045] FIG. 28 is a schematic view depicting a portion of apparatus
according to yet another embodiment of the invention.
[0046] FIG. 29 is an elevational view depicting apparatus according
to a still further embodiment of the invention.
[0047] FIG. 30 is a fragmentary view on an enlarged scale of a
portion of the apparatus shown in FIG. 29.
[0048] FIG. 31 is a view similar to FIG. 29, but depicting
apparatus according to a further embodiment of the invention.
[0049] FIG. 32 is a schematic diagram depicting apparatus according
to yet another embodiment of the invention.
[0050] FIG. 33 is a view similar to FIG. 32, but depicting
apparatus according to yet another embodiment of the invention.
[0051] FIG. 34 is a fragmentary schematic view depicting apparatus
according to a still further embodiment of the invention.
[0052] FIG. 35 is a diagrammatic sectional view depicting apparatus
to yet another embodiment of the invention.
[0053] FIG. 36 is a fragmentary, diagrammatic sectional view
depicting apparatus according to yet another embodiment of the
invention.
[0054] FIG. 37 is a diagrammatic, partially sectional, partially
perspective view depicting apparatus according to a still further
embodiment of the invention.
[0055] FIG. 38 is a diagrammatic sectional view depicting apparatus
according to yet another embodiment of the invention.
[0056] FIG. 39 illustrates an exemplary structural balloon.
DETAILED DESCRIPTION
[0057] As seen in FIG. 1, apparatus according to one embodiment of
the invention includes an insertable structure 10 incorporating an
elongated catheter 12 having a proximal end 14, which remains
outside of the body, and a distal end 16 adapted for insertion into
the body of the subject. As used in this disclosure with reference
to structures which are advanced into the body of a subject, the
"distal" end of such a structure should be taken as the end which
is inserted first into the body and which penetrates to the
greatest depth within the body, whereas the proximal end is the end
of the structure opposite to the distal end. The insertable
structure 10 also includes an ablation unit 18 mounted to the
catheter adjacent distal end 16. Ablation unit 18 incorporates a
reflector balloon 20 and a structural balloon 22 having a common
wall 24. Reflector balloon 20 is linked to an inflation lumen (not
shown) in catheter 10, which extends to the proximal end of the
catheter and which is connected, during use, to a source of a gas
under pressure, such as air or, more preferably, carbon dioxide,
as, for example, to a gas-filled hypodermic syringe, so that the
reflector balloon can be inflated with a gas. Structural balloon 22
is connected through a separate inflation lumen (also not shown) to
a source of a liquid such as isotonic saline solution, so that
structural balloon 22 can be inflated with the liquid. A
cylindrical ultrasonic emitter 23 is mounted within the structural
balloon. Balloons 20 and 22, and particularly the common wall 24
separating the balloons, are designed so that in their inflated,
operative condition illustrated in FIG. 1, the balloons are in the
form of bodies of revolution about a central or forward-to-rearward
axis 26. Emitter 23 is cylindrical and is coaxial with the
balloons.
[0058] A tube 28 extends through the structural balloon at the
central axis 26. Tube 28 defines a port 29 on or forward of the
forward wall 38 of the structural balloon. Tube 28 communicates
with a lumen 30 within catheter 12. Lumen 30 extends to the
proximal end 14 of the catheter and is provided with a suitable
fluid connection such as a Luer hub. The bore of tube 28 and lumen
30 of catheter 16 form a continuous passageway extending from the
outlet port 29, just distal to the ablation device back to the
proximal end 14 of the catheter. As further described in
co-pending, commonly assigned U.S. patent application Ser. No.
10/244,271, filed Sep. 16, 2002, published as US/2004/0068257-A1
("the '257 application") and granted as U.S. Pat. No. 7,189,229,
the disclosure of which is incorporated by reference herein, tube
28 may be formed from a material such as an expanded polymer of the
type commonly used in vascular grafts, so that the interior bore of
the tube remains patent when the tube is stretched. As also
disclosed in the '257 application, a coil spring 34 may be provided
within the structural balloon, such that the coil spring surrounds
tube 28. A reinforcing structure which may include one or more
rigid tubes of metal or a rigid polymer such as polyether ether
ketone ("PEEK") 36 desirably surrounds tube 28 and spring 34. As
described in greater detail in the '257 application, the spring is
compressed when the balloons are in the inflated, operative state.
When the balloon is deflated, the spring expands and moves the
forward wall 38 of the structural balloon in the forward or distal
direction F (up and to the left, as seen in FIG. 1) relative to the
rearward or proximal end of the balloon and relative to the
catheter 12, thereby collapsing the balloon in a radial direction,
and also twists the balloons about axis 26 to facilitate radial
collapse and formation of a small, radially compact unit for
withdrawal from the patient. However, when the balloons are
inflated, the spring is compressed and reinforcing element 36
engages a rigid mounting 40 attached to the distal end 16 of the
catheter, which mounting also holds ultrasonic emitter 23. This
assures that the axis 26 of the balloon structure is precisely
aligned with the axis of the emitter and reinforces the balloon
against deflection transverse to the axis 26.
[0059] In the arrangement depicted in FIG. 1, the tubular
reinforcing element 36 abuts the distal end of the mounting 40. In
a variant, the mounting is telescopically received within the
tubular reinforcing element. Thus, as the balloons are inflated,
the tubular reinforcing element 36 moves proximally or rearwardly
so that the distal end of the mounting 40 enters into the tubular
reinforcing element before the balloons are fully inflated. In the
fully-inflated condition, the tubular reinforcing element remains
slightly distal or forward of the transducer 23 or else abuts the
distal end of the transducer. Telescopic engagement between the
mounting and the reinforcing element helps prevent kinking or
displacement of the structure transverse to axis 26 when the
structure is in a partially-inflated or fully-inflated
condition.
[0060] As discussed in the '257 application and in the '512
publication, the common wall 24 separating the balloons forms an
active, reflective interface. This active interface desirably has
the form of a surface of revolution of a parabolic section around
the central axis 26. When the balloons are in their inflated,
operative configuration shown in FIG. 1, ultrasonic waves emitted
by emitter 23 are directed radially outwardly away from axis 26 and
impinge on the parabolic active interface 24, where it is reflected
forwardly and slightly outwardly away from axis 26 and focused so
that the ultrasonic waves emitted along various paths mutually
reinforces within a ring-like ablation region A, just forward of
the forward wall 38 of the structural balloon encircling axis 26.
The focused ultrasonic waves in this region can effectively ablate
myocardial tissue and form a substantial conduction block extending
through the heart wall in a relatively short time, typically about
a minute or less.
[0061] In a method according to one aspect of the present
invention, the apparatus is positioned within a chamber of the
heart as, for example, within the left atrium LA of a subject to be
treated. A guide sheath (not shown) is advanced through the venous
system into the right atrium and through the septum separating the
right atrium and left atrium, so that the guide sheath provides
access to the left atrium. Typically, the apparatus is advanced
through the guide sheath with the balloons in a deflated condition.
The threading operation may be performed by first threading a guide
wire (not shown) into the heart, then advancing the guide sheath
(not shown) over the guide wire, and then advancing the insertable
structure 10, with the balloons in a deflated condition, over the
guide wire, and through the guide sheath. In this operation, the
guide wire passes through tube 28 and through lumen 30. When the
apparatus is positioned within the heart so as to place the
ablation zone A within the heart wall W and around the ostium OS of
a pulmonary vein, the ultrasonic emitter 23 is activated.
[0062] According to one aspect of the present invention, the
correct positioning of the ablation device can be verified by the
use of a contrast medium such as an x-ray contrast medium. After
threading, the guide wire may be removed and lumen 30 may be
connected, as by Luer fitting 32 to a source 44 of an x-ray
contrast medium as, for example, a hypodermic syringe filled with
the contrast medium. To verify proper placement of the ablation
device, the contrast medium is injected through lumen 30 and passes
through the bore of tube 28 and out through port 29 at the forward
wall 38 of the structural balloon. The injected contrast medium C
has sufficient velocity to carry it distally, into the ostium and
into the pulmonary vein. The blood flow in the pulmonary vein PV,
directed back toward the ostium and into the left atrium LA,
carries the contrast medium back into the left atrium and around
the ablation device.
[0063] While the contrast medium is injected and during spread of
the contrast medium into the left atrium, the patient is imaged
using an x-ray imaging modality, most preferably a fluoroscope.
This allows the physician to immediately visualize the shape and
size of the ostium and the position of the ablation device relative
to the ostium and relative to the heart wall W. Provided that the
positioning is satisfactory, the physician actuates the ultrasonic
emitter 23 to emit the ultrasonic waves and ablate the tissue of
the heart wall.
[0064] In a variant of the procedure discussed above, a thin,
tubular stylet 50 (FIG. 2) having an outlet port at its distal end
52 is threaded through the continuous passageway defined by lumen
30 and by the bore of tube 28, so that the distal end 52 of the
stylet projects forwardly to the distal end of the balloon.
Preferably, the distal end of the stylet does not project
substantially beyond the distal end of the balloon, and hence
cannot extend substantially into the pulmonary vein. Therefore the
stylet cannot damage the lining of the pulmonary vein. The proximal
end 54 of the tubular stylet is equipped with a connection such as
a hub 56 which, in turn, is connected to the contrast medium source
44. Stylet 50 may serve as the guide wire used in threading the
assembly into the patient. Thus, stylet 50 may be placed prior to
catheter 12 and ablation device 18. In this case, the connection at
proximal end 54 may incorporate a removable hub so that the
catheter and ablation device assembly may be threaded over the
stylet and then, after the catheter is in place, hub 56 may be
added to the proximal end of the stylet. Alternatively, the
assembly may be threaded using a conventional guide wire which is
then removed and replaced by the stylet. The stylet 50 may be
relatively stiff, so that the stylet positions the ablation device
relative to the pulmonary vein and relative to the heart.
Positioning the balloon at the PV ostium with a stylet is
advantageous if there is no clear PV main trunk or the axis of the
trunk of the PV is not substantially perpendicular to the wall of
the atrium. The distal end 52 of the tubular stylet 50 defines an
outlet port for the contrast medium or the distal side of the
ablation device. Here again, the contrast medium introduced through
the port. When the contrast medium C is introduced into the patient
through this port, it permits visualization of the ablation device
18, pulmonary vein PV, ostium OS and heart wall W, in the manner
discussed above, thereby allowing the physician to confirm proper
position of the device.
[0065] In a further variant, a guide wire having an outside
diameter smaller than the inside diameter of the catheter lumen 30
and smaller than tube 28 may be left in place while contrast medium
is introduced through the continuous passageway defined by the
lumen and tube. Because the guide wire does not completely occlude
the passageway, the contrast medium can flow through the passageway
and pass out of the port 29 in the manner discussed above with
reference to FIG. 1.
[0066] In yet another variant of the procedures discussed above,
the ablation device 18 may be positioned so that the distal wall 38
abuts the heart wall W in the vicinity of the pulmonary vein ostium
and thus substantially occludes and thus substantially blocks flow
between the pulmonary vein PV and the heart chamber itself.
Contrast medium is injected through port 29 of the ablation device
itself as discussed with reference to FIG. 1, or through the port
52 of a hollow style as discussed with reference to FIG. 2, while
the ablation device is in this blocking position. This increases
the concentration of the contrast medium within the pulmonary vein
and ostium, and thus facilitates imaging of pulmonary vein and
ostium and adjacent structures with a minimal amount of contrast
medium. Optionally, the catheter and ablation device may be
retracted after acquiring an image of the ostium and vein, allowing
the contrast medium to flow into the atrium, and further images may
be acquired.
[0067] A significant advantage of the procedures discussed above
with reference to FIGS. 1 and 2 is that disposition of the ablation
device relative to anatomical structures can be verified while the
ablation device is in its inflated, operative condition. Such
verification can be performed immediately before, during or after
application of ultrasonic waves. The ultrasonic waves will
propagate effectively through typical liquid x-ray contrast media,
inasmuch as the media have acoustic impedance similar to that of
other aqueous liquids. There is no need to move any portion of the
ablation device or catheter during introduction of the contrast
medium and visualization.
[0068] As also shown in FIG. 2, positioning of the ablation device
within the heart desirably includes selectively controlling the
disposition of the forward-to-rearward axis 26 of the device
relative to the patient's heart. That is, the position of the
forward-to-rearward axis desirably can be controlled by the
physician to at least some degree. For example, the device may be
arranged so that the physician can selectively reorient the
forward-to-rearward axis 24 of the ablation device through a range
of motion as, for example, through the range between disposition
indicated in solid lines by axis 24 and the disposition indicated
in broken lines by axis 24'. To that end, the assembly can be
provided with one or more devices for selectively varying the
curvature of a bendable region 60 of the catheter just proximal to
the ablation device.
[0069] In one embodiment, shown schematically in FIGS. 3 and 4, the
catheter is provided with one or more pull wires 64. Each such pull
wire extends from the proximal end 14 of the catheter in a bore or
lumen 66 dimensioned to provide a free-running fit for the pull
wire. Each pull wire has a distal end 68 fastened to the catheter
wall. The distal ends of the pull wires are disposed at or distal
to the bendable region 60. By pulling on a particular wire 64, the
bendable region 60 can be bent in the direction toward that
particular pull wire. As best seen in FIG. 4, the particular
embodiment illustrated has four pull wires disposed in two sets
lying in orthogonal planes. The first set includes pull wires 64A
and 64B, whereas the second set includes pull wires 64C and 64D.
This permits bending of the bendable region in substantially any
direction by selectively pulling two of the wires. However, a
lesser number of pull wires can be used. For example, a version
with three pull wires also permits selective bending in any
direction, whereas a version with two diametrically opposite pull
wires permits selective bending in either of two opposite
directions in a single plane. In an even simpler arrangement, only
a single pull wire is provided to provide bending in only a single
direction. The catheter itself, or at least the bendable region 60,
may be resilient so that it tends to return to a predetermined
configuration, such as a straight configuration, when the single
pull wire is released. Even a version which permits bending of
region 60 in only a single plane provides considerable ability to
position the ablation device. For example, the catheter may be
"torqueable" or arranged to transmit rotation in the direction
around the central axis 70 of the catheter itself. In such an
arrangement, combined bending of region 60 and rotation of the
catheter about it own axis 70 allows movement of the
forward-to-rearward axis of the ablation device towards essentially
any desired disposition.
[0070] The lumens 66 containing the pull wires 64 may be provided
with coil springs (not shown) lining the lumens, so that each pull
wire extends though the interior of one such coil spring. The turns
of each coil spring form a low-friction liner within the associated
lumen. Moreover, the coil springs can provide additional structural
reinforcement and resilience to the catheter.
[0071] In a variant of this approach, the bendable section 160 of
the catheter is attached to one or more pull wires 164 which extend
outside of the catheter at the bendable section itself. Each such
pull wire may extend through a bore 165 in the catheter proximal to
the bendable section. By pulling on wire 164, the bendable section
can be deformed to the bent configuration shown in broken lines at
160'. In this configuration, the pull wire 164 extends as a chord
164' across the arc formed by the bendable section. Here again, two
or more pull wires may be provided to permit selective deformation
in multiple directions, or else a single pull wire can be used in
conjunction with a torqueable catheter which can be rotated about
its own axis by turning the proximal end of the catheter. In a
further variant, the pull wires may extend entirely outside of the
catheter. For example, where a guide sheath surrounds the catheter
proximal to the bendable section, pull wires may extend within the
guide sheath. In a further embodiment, the distal ends of the pull
wires can be attached to the ablation device itself, rather than to
the catheter. In yet another variant, the pull wires may serve as
electrical conductors for energizing the ultrasonic element or for
other purposes as, for example, conducting signals to or from
sensors used to detect electrical potentials in the heart,
electromagnetic position detection devices, ultrasonic or other
imaging devices and other electronic components mounted on or near
the distal end of the catheter.
[0072] As seen in FIG. 6, the bendable section 260 of the catheter
may be selectively deformed to the curved shape illustrated in
solid lines by advancing a stylet 261 having a predetermined
curvature through the lumen 230 of the catheter. The stylet may be
formed from a metal or plastic and may be solid or, preferably,
hollow, so as to leave a space for introduction of the contrast
medium as described above through lumen 230. The stylet may have
different properties at different points along its length. Thus,
the curved section 261 may be carried by a more flexible section
263 proximal to the curved section and a further, more flexible
section 265 may be provided distal to the curved section. Such a
stylet may be used as the contrast medium introducing stylet 50
discussed above with reference to FIG. 2. The stylet is positioned
so that the curved section 261 is located in the bendable region of
the catheter. Prior to introduction of the stylet, the physician
may deform curved section 261 to provide a selected degree of
curvature. For example, the ablation device may be brought to its
expanded, operative condition within the heart and imaged using
contrast medium as discussed above, so that the physician can
estimate the amount of curvature required in the bendable section
to align the device properly with the heart, and the stylet may be
curved accordingly and introduced into the catheter. Following
introduction of the stylet, the imaging procedure can be repeated
to check for proper placement. Desirably, the curved section 261 of
the stylet has at least some resilience so that the curved section
can be partially or completely straightened during threading, as
the curved section is advanced from the proximal end of the
catheter to the bendable section. Those sections of the catheter
proximal to the bendable section desirably are more rigid than the
bendable section. Thus, the bendable section may have a lesser wall
thickness or be formed from a more flexible material than the
proximal portions of the catheter. Also, the proximal portions of
the catheter may be encased in a guide sheath 267, which terminates
proximal to the bendable section.
[0073] In a further variant, a guide sheath 367 having a selected
curvature is advanced over the bendable section 360 of the catheter
so as to deform the bendable section from a straight or other
configuration 360', shown in broken lines, to a curved
configuration, as shown in solid lines, having the selected
curvature matching the curvature of the sheath. Sheath 367 extends
to the proximal end of the catheter (not shown) so that the sheath
can be manipulated while the device is in place. Thus, by advancing
or retracting the sheath, the physician can control the degree of
curvature of bendable section 360. In another embodiment, the
bendable section of the catheter may be resilient and may be curved
when in its normal or un-stressed condition, without external loads
applied. The bendable section can be straightened during threading
through the guide sheath. As the catheter is advanced so that the
bendable section protrudes beyond the guide sheath, the bendable
section returns to its normal condition. The amount of curvature
can be increased by advancing the catheter distally relative to the
guide sheath, or decreased by retracting the catheter. The catheter
or guide wire also may incorporate a shape memory alloy such as
Nitinol (trademark) which tends to assume a predetermined shape
when heated to body temperature.
[0074] In yet another variant, a sheath may include features which
permit steering of the sheath. Such a steerable sheath can be bent
in a desired direction and used to bend the catheter in a desired
direction. A steerable sheath may be used in conjunction with a
steerable catheter. For example, a steerable, torqueable sheath may
be used in conjunction with a steerable catheter having a bendable
section which is constrained by the sheath and having a further
bendable section projecting distally beyond the sheath. Such an
arrangement provides a compound steering action, so that two
independent bends can be imparted to the catheter. These bends may
be in the same plane or in two different planes. In the embodiments
discussed above, the catheter is formed separately from the guide
sheath used to introduce the catheter into the left atrium.
However, this is not essential; the functions of the catheter and
the guide sheath may be combined. In such an arrangement, the
combined guide sheath and catheter desirably has a distal portion
bearing the ablation device and a proximal portion arranged so that
the distal portion and the ablation device, including the balloon
structure, can be moved between a retracted position in which the
ablation device is contained within the proximal portion and an
extended position in which the ablation device protrudes from the
retracted portion. Where the ablation device incorporates an
expansible structure such as the balloon structures discussed
above, the expansible structure is in a collapsed condition, and is
located near the distal end of the proximal portion, when the
distal portion is in the retracted position. The proximal portion
desirably has the strength and physical properties required for
threading through the vascular system and through the fossa ovalis.
The combined structure avoids the need to advance the expansible
structure through the entire length of the guide sheath during the
procedure.
[0075] Apparatus according to a further embodiment of the invention
incorporates a catheter having a bendable section 460 which
desirably is resilient. The ablation device 418 in this embodiment
also includes a structural balloon 422 and reflector balloon 420,
and an emitter 423 similar to those discussed above with reference
to FIG. 1. An additional inflatable structure 402 is mounted to the
bendable section proximal to the ablation device. Inflatable
structure 402 is connected to an inflation lumen 404 extending
within the catheter to the proximal end thereof. This inflation
lumen is separate from the inflation lumen 406 used to inflate the
reflector balloon 420 and separate from the inflation lumen (not
shown) used to inflate structural balloon 422. With structure 402
deflated, bendable section 460 has a curved configuration as seen
in FIG. 8, such that the forward-to-rearward axis 426 of the
ablation device lies at an arbitrary angle to the axis 407 of the
catheter proximal to the bendable section. However, by inflating
structure 402 to the inflated condition 402' (FIG. 9), the bendable
section 460 can be straightened so as to substantially align the
forward-to-rearward axis 426' of the ablation device 418 with the
axis 407 of the catheter proximal to the bendable section.
Structure 402 can be inflated using a gas or a liquid. Also,
structure 402 need not be fully inflated; by varying the degree of
inflation, the physician can control the orientation of the
ablation device relative to the heart. To permit selective
inflation and deflation of structure 402', the associated inflation
lumen 404 extends to the proximal end of the catheter and is
connected to a controllable fluid source as, for example, a syringe
or other pumping device, or a tank containing fluid under pressure
linked to the inflation lumen through a controllable pressure
regulator. Bendable section 460 may be resilient so that it tends
to assume a curved shape, as seen in FIG. 8, when structure 402 is
deflated. Alternatively, the curvature of the bendable section with
inflatable structure 402 deflated may be caused by anatomical
structures bearing on the ablation device, on the catheter, or
both. In either case, inflation of structure 402 will tend to
straighten the bendable section and swing the forward-to-rearward
axis of the ablation device. In a variant of this approach, the
bendable section may be straight when not subjected to external
forces and may be deformed to a curved shape by inflation of
structure 402.
[0076] In a further variant, the separate inflatable structure 402
may be omitted, and pressure differentials within the lumens of the
catheter, such as lumens 404 and 406 (FIG. 8) may act to bend or
straighten the catheter. For example, if the gas pressure in lumen
404 is less than the gas pressure in lumen 406, the catheter will
tend to bend into a curve as depicted in FIG. 8. The reverse
pressure differential (higher pressure in lumen 404 than in lumen
406) will tend to straighten the catheter or bend it in a curve
opposite to that depicted in FIG. 8. To provide a high differential
pressure, one of the lumens may be connected to a vacuum pump
whereas another lumen may be connected to a source of a gas or
liquid under super-atmospheric pressure.
[0077] In a further modification, (FIG. 10), an inflatable
structure 401 is mechanically connected between catheter section
461 proximal to the ablation device 418 and the ablation device
itself as, for example, between the catheter and the proximal wall
of reflector balloon 420. Thus, when inflatable structure 401 is
deflated, the ablation device may be tilted relative to the
catheter, as indicated in broken lines at 418'. However, when the
inflatable structure 401 is inflated, as seen in solid lines, the
ablation device is brought to the condition depicted in solid
lines, as by bending of the catheter adjacent the ablation device.
Here again, inflation or deflation of the inflatable structure
turns the forward-to-rearward axis of the ablation device relative
to the proximal regions of the catheter and also relative to the
heart and surrounding structures.
[0078] In a further variant (FIG. 11), the interior space within
inflatable structure 401 communicates with the interior space of
reflector balloon 420. Thus, the degree of inflation of structure
401 and, hence, the disposition of the ablation device, can be
controlled by varying the pressure within reflector balloon 420.
Thus, the position of the catheter can be varied by varying the gas
pressure applied to the reflector balloon inflation lumen 406. In
this regard, operation of the ablation device itself does not vary
significantly with gas pressure inside reflector balloon 420;
provided that the gas pressure within the reflector balloon is
sufficient to move the wall of reflector balloon 420 away from the
common wall or active interface 424 separating the reflector
balloon and the structural balloon, the active interface will
provide the desired ultrasonic reflective interface.
[0079] In a further variant, inflatable structure 401 may have a
wall structure different from the wall of the reflector balloon, so
that the inflatable structure will only inflate to a substantial
degree after the gas pressure inside reflector balloon reaches a
certain threshold value.
[0080] In yet another variant, the inflatable structure 401 may be
formed as an extension of the reflector balloon along one side of
the catheter.
[0081] In a further variant, seen in sectional view facing axially
along the catheter at FIG. 12, plural inflatable structures 502 are
provided around the circumference of the catheter 560, and the
separate inflatable structures are provided with separate inflation
lumens 504. This allows selective bending in multiple directions by
controlling the gas pressures within the various inflation
structures. Here again, each of these structures may bear on the
proximal side of the ablation device, which may be configured as
shown in FIGS. 8 and 9, so that each structure extends only along
the bendable portion of the catheter.
[0082] In yet another variant (FIG. 13), a plurality of inflatable
structures 602 are provided around the circumference of the
catheter and, hence, spaced around the axis 626 of the ablation
device 618. These inflatable structures are arranged so that they
bear on the heart wall W or other anatomical structure when
inflated and, thus, move the ablation device 618 relative to the
heart. Each inflatable structure 602 is independently inflatable or
deflatable as, for example, by a separate inflation lumen (not
shown) extending to the proximal end of the catheter.
[0083] Inflatable structures 602 optionally may serve as reflector
balloons of the ablation device. Thus, two or more such structures
cooperatively surround axis 626 at the proximal side of the
structural balloon, and each such inflatable structure defines a
common wall with the structural balloon. Separating walls 605
segregate the individual inflatable structures 602 from one
another. Provided that all of the inflatable structures are
inflated with a minimal gas pressure sufficient to provide gas at
this common wall or interface 624, the structure will provide
substantially the same ultrasonic reflecting action as the single
reflector balloon discussed above. To the extent that any
non-reflective regions at the separating walls 605 cause gaps in
the ablation, this can be overcome by rotating the catheter so as
to rotate the ablation device about axis 626 and repeating the
ultrasonic application step. Alternatively, one or more of the
inflatable structures 602 may be left entirely deflated, or may be
inflated with a liquid, so as to render a portion of the
interfacial wall 624 non-reflective to ultrasound. In this case,
the emitted ultrasound is focused only on an arcuate portion of the
ring-like focal region. This can be used, for example, where the
anatomical structure of the patient makes it undesirable to ablate
the entire ring.
[0084] Apparatus according to a further embodiment includes a
catheter 1302 (FIG. 14) having a proximal end 1301, a distal end
1303, and an expansible structure including a reflector balloon
1304 and a structural balloon 1306 similar to those discussed above
with reference to FIG. 1 attached to the distal end of the
catheter. As seen in FIG. 20, catheter 1302, at least at its distal
end, includes a circular outer wall 1308, a central tubular wall
1310 defining a principal or central lumen 1312 and a set of webs
1314 extending between the tubular wall 1310 and the other wall so
that the tubular wall, outer wall, and webs cooperatively define a
first additional lumen 1316, a second additional lumen 1318, and a
third additional lumen 1320 disposed in the periphery of the
catheter, around the central lumen. A reinforcing structure 1321
including an emitter assembly 1322 and an extensible structure 1392
(FIG. 14) is mounted to the distal end of the catheter. Emitter
assembly 1322 includes a proximal mounting structure 1324, a
hollow, tubular piezoelectric element 1326, and a distal mounting
structure 1328. These features are shown on a greatly enlarged
scale in the drawings; in actual practice, the catheter 1302
typically has an outside diameter on the order of 3-4 mm.
[0085] As best seen in FIGS. 15 and 16, the proximal mounting
structure 1324 is formed as a generally cylindrical metallic shell
having a proximal end 1330 and a distal end 1332. Three thick
metallic ribs 1334 extend inwardly from the shell at the proximal
end 1330 of the structure. These ribs terminate short of the distal
end 1332 so as to leave a pocket 1336 adjacent the distal end of
the structure. Ribs 1334 define a first side channel 1340, a second
side channel 1342, and a slot 1344. A port 1346 extends through the
outer wall of the shell and intersects the second side channel
1342.
[0086] The distal mounting structure 1328 includes a solid
cylindrical body 1348 with a central bore 1350 extending through
the body and coaxial with the other periphery of the body. Three
projections 1352 extend proximally from the body. Projections 1352
are spaced around the periphery of the body and define slots 1354
extending radially inwardly between them. Each projection 1352 has
a stop surface 1356 facing in the proximal direction and a contact
portion 1358 projecting slightly beyond the stop surface 1356 in
the proximal direction (to be left as seen in FIG. 17). A skirt
1360 projects from the distal end of body 1348. Skirt 1360 defines
a cylindrical exterior surface coaxial with bore 1350 and a
frustoconical interior pocket 1362, also coaxial with bore 1350.
Pocket 1362 is slightly narrower at its proximal end (at the
juncture with body 1348) then at its open, distal end. Preferably,
skirt 1360 tapers outwardly at an included angle of about 110.
[0087] Tubular piezoelectric element 1326 has an exterior surface
visible in FIGS. 14, 19, and 21 and an interior surface 1364 (FIG.
20). Electrically conductive metallic coatings (not shown) overlie
both the exterior and interior surfaces of piezoelectric element.
The piezoelectric element typically is formed from piezoelectric
ceramic such as that sold under the commercial designation PZT-8.
As best seen in FIGS. 19-21, piezoelectric element 1326 is engaged
with the distal end of the proximal mounting structure 1324. The
proximal end of the transducer is lodged within the cylindrical
pocket 1336 at the distal end of the structure. The piezoelectric
element is soldered or otherwise physically and electrically
connected to the proximal mounting structure. Distal mounting
structure 1328 is secured to the distal end of the piezoelectric
element 1326. The distal end of the tubular piezoelectric element
abuts the stop surfaces 1356 (FIG. 17) of the distal mounting
structure. The contact portions 1358 of the projections on the
distal mounting structure extend into the interior of the
piezoelectric element. The distal mounting structure is
electrically and mechanically bonded to the inside surface of the
piezoelectric element as by soldering.
[0088] A thin-walled, electrically-conductive and preferably
metallic tube 1370, referred to herein as the "inside tube," is
supported by the ribs 1334 of the proximal end element, but
electrically insulated from the proximal end element by a short
hollow insulator 1372 formed from a dielectric material as, for
example, a thin coating of polymer on the exterior surface of the
inside tube. The inside tube extends through the interior of
piezoelectric element 1326. The distal end of inside tube 1370 is
engaged in the distal mounting structure 1328 (FIG. 21). The inside
tube defines a bore 1374. The bore of the inside tube is aligned
with and continuous with the bore 1350 (FIG. 18) of the distal
mounting structure. The outside diameter of inside tube 1370 is
substantially smaller than the inside diameter of the transducer
element 1326. However, the proximal and distal mounting structures
maintain tube 1370 substantially coaxial with transducer 1326. The
exterior surface of tube 1370 and the interior surface 1364 (FIG.
20) of the transducer 1326 cooperatively define an annular
passageway 1376 extending from the proximal end of the
piezoelectric element to its distal end. Passageway 1376
communicates, at its proximal end, with the first channel 1326 in
the proximal mounting structure and also with the second channel
1318 of the proximal mounting structure. At its distal end, the
annular passageway inside piezoelectric transducer 1326
communicates with the slots 1354 in the proximal mounting
structure. The entire emitter assembly 1322, including the proximal
and distal mounting structures piezoelectric element and inside
tube forms a rigidly connected unit.
[0089] The rigid transducer assembly 1322 is mounted to the distal
end of the catheter 1302 so that the first channel 1340 in the
proximal mounting structure (FIG. 16) is aligned with the first
additional lumen 1316 of the catheter, whereas the second channel
1342 is aligned with the second additional lumen 1318 of the
catheter. Thus, both the first and second additional lumens 1316
and 1318 of the catheter communicate with the annular passageway
1376 inside the piezoelectric element, whereas the second
additional lumen 1318 communicates with port 1346 (FIGS. 19 and 15
and 16) through the second side channel 1342 of the proximal
mounting structure. Inside tube 1370 is aligned with the principal
lumen 1310 of the catheter so that the bore 1374 of the central
tube communicates with the principal lumen. Slot 1344 of the
proximal mounting structure is aligned with the third additional
lumen 1320 of the catheter.
[0090] A small coaxial cable 1380 extends through the third
additional lumen 1320 of the catheter. This coaxial cable has a
first conductor in the form of a sheath 1382 and a central
conductor 1384 separated from sheath 1382 by a dielectric jacket.
Sheath 1382 is electrically connected to the proximal mounting
structure 1324 within slot 1344. The jacket 1382 is electrically
connected through the proximal mounting structure 1326 to the
outside surface of piezoelectric element 1326. The central
conductor 1384 extends into the annular passageway 1376 and is
bonded to the inside tube 1370, so that the central conductor 1384
is electrically connected by inside tube 1370 and distal mounting
structure 1328 to the inside surface of the piezoelectric
element.
[0091] A pull wire 1385, most preferably a metallic wire, has a
distal end fixed to the emitter assembly 1322 by welding or
otherwise fixing the pull wire to the proximal mounting structure
1324. Pull wire 1385 extends through the third additional lumen
1320 to the proximal end 1301 of the catheter and is connected to a
handle 1387 so that the physician can selectively pull or push on
the pull wire during use. Typically, the handle is integrated with
another handle (not shown) attached to the proximal end 1301 of the
catheter, so that the physician can manipulate both the catheter
and the guide wire. For example, the handle for the catheter may
carry a separate knob for other manual control device so that the
physician can manipulate the catheter by manipulating the handle
and manipulate the guide wire by manipulating the knob or the
control device.
[0092] The structural balloon 1306 (FIG. 14) is mounted on the
catheter so that port 1346 communicates with the interior of this
balloon adjacent the proximal end thereof and proximal to
transducer 1326. The third additional lumen 1320 of the catheter
preferably is isolated from the annular passageway 1376 and from
the interior of the structural balloon 1306. For example, any
portion of slot 1344, which is not occupied by portions of the
coaxial cable 1380 extending through it may be filled with a
bonding material such as an adhesive or a solder. Third peripheral
lumen 1320 desirably communicates with the interior of reflector
balloon 1304 (FIG. 14) through an opening (not shown) in the
peripheral wall 1308 of the catheter.
[0093] The structural balloon 1306 has a distal end fitting 1388.
An extensible structure 1392 extends between the emitter assembler
1322 and the distal end fitting 1388. As best seen in FIG. 22, the
distal end fitting 1388 includes a cylindrical outer surface.
Structural balloon 1306 has a hollow cylindrical distal neck 1393,
which closely fits over this outer surface and is bonded thereto by
an adhesive. End fitting 1388 also includes a through bore
extending between its proximal end and its distal end. The distal
end of such through bore defining an outlet port opening 1390 just
forward of the distal face of the balloon. The distal end fitting
further includes one or more transverse bores 1391 (FIG. 22), which
extend transverse to the central bore or outlet port opening 1390,
and which also communicates with the exterior of the fitting.
[0094] Extensible structure 1392 includes a supple, distensible
tube 1394 having its distal end connected to the distal end fitting
1388 and having its proximal end connected to emitter assembly
1322. In the arrangement shown, the proximal end of tube 1394
envelops the exterior of skirt 1360 on the distal mounting
structure 1328. The extensible structure also includes a first
engagement element in the form of a reinforcing tube 1396 fastened
to the distal end fitting 1388 and having a bore 1398 communicating
with the outlet port opening 1390. The extensible structure 1392
further includes a proximal reinforcing tube 1400. The proximal end
tube 1400 is fixed in the seat 1362 of the distal mounting
structure 1398. The proximal reinforcing tube, and emitter assembly
1322 cooperatively constitute a second engagement element. As seen
in FIG. 22, there is clearance between the outside surface of
proximal reinforcing tube 1400 and skirt 1360 adjacent the open
distal end of the conical seat 1362. The distal end of proximal
reinforcing tube 1400 is telescopically received within the bore
1398 of the distal reinforcing tube 1396.
[0095] As shown in FIG. 22A, the distal end of proximal reinforcing
tube 1400 has a small flange 1397 projecting outwardly, whereas the
proximal end of distal reinforcing tube 1396 has a small
inwardly-directed flange 1401. These features interlock with one
another so that the reinforcing tubes cannot be disengaged from one
another.
[0096] As will be appreciated with reference to FIG. 22, the
structure provides a continuous passageway through the outlet port
1390 and the bore of distal end fitting 1380, through the bore 1398
of the distal reinforcing tube, through the bore 1402 of the
proximal reinforcing tube and the bore 1350 of distal mounting
structure 1350 into the bore 1374 of the inside tube 1370, which in
turn communicates with the central, principal lumen 1312 of the
catheter. As the principal lumen of the catheter extends to the
proximal end of the catheter (FIG. 14), the structure provides a
continuous passageway from the proximal end of the catheter through
the emitter and balloon structures through the outlet port opening
1390 on the distal side of structural balloon 1306. This continuous
passageway is sealed from the interior balloon 1306 and from the
annular passageway 1376 inside the piezoelectric element 1326. The
distensible tube 1394 blocks any leakage between the telescoping
reinforcing tubes 1396 and 1400.
[0097] A coil spring 1406 surrounds the reinforcing tubes. The
distal end of the coil spring bears on the distal end fitting 1388
and preferably is welded or otherwise securely attached to the
distal end fitting 1388. The proximal end of spring 1406 bears on
the distal mounting structure 1328 of the emitter assembly 1322.
Spring 1406 is also securely attached to the distal mounting
structure 1328 of the emitter assembly as by welding the spring to
the mounting structure.
[0098] In the deflated, collapsed condition depicted in FIG. 22,
spring 1406 is in a substantially relaxed condition. The extensible
structure 1392 is in an extended state in which the distal ending
fitting 1388 and the distal end of balloon 1306 are remote from the
emitter assembly 1322. In this condition, also referred to as a
disengaged condition, the distal reinforcing tube 1396 remote from
the seat 1362 of the emitter assembly 1322. Also, the distal
reinforcing tube covers only a small portion of the proximal
reinforcing tube 1400. In this condition, the extensible structure
1392 can flex to a significant degree. The reinforcing tubes 1396
and 1394 are thin-walled structures. These tubes desirably have
outside diameters on the order of 1-2 mm. Moreover, the tapered
seat 1362 does not appreciably restrict flexing of the proximal
reinforcing tube 1400. Further, there is a slight clearance between
the outside of flange 1397 on proximal tube 1400 and the inside of
distal tube 1396, which contributes to flexibility of the assembly.
To further increase the flexibility of the assembly, the
reinforcing tubes may have openings such as slots or holes in their
walls.
[0099] In the deflated condition, the structural balloon 1306, as
well as the reflector balloon 1304 are in a twisted condition so
that they wrap gently around the extensible structure 1392 emitter
assembly 1322 and the distal end of the catheter 1302. Thus, all of
the structures at the distal end of the catheter form a slender
assembly capable of passing through a bore of about 0.187 inches
(4.74 mm) inside diameter in a guide sheath or other structure.
This assembly is flexible due to the flexibility of the extensible
structure. However, the extensible structure, and particularly the
telescoped reinforcing tubes are substantially resistant to
kinking. The catheter is also flexible. The entire assembly can be
advanced and placed into a chamber of the heart, typically the left
atrium in the manner discussed above. A guide wire (not shown) may
be placed through the aforementioned continuous passageway
including the central lumen of the catheter and the bores 1374,
1402, and 1398 of the aforementioned tubes, so that the guide wire
extends out through the outlet bore 1390 at the distal end of the
assembly.
[0100] The catheter and associated elements are used in cooperation
with operating apparatus including a liquid supply unit 1410
arranged to supply a cool liquid under pressure and a liquid drain
1412 connected to the second peripheral lumen 1318 of the catheter
at its proximal end. The liquid supply 1410, liquid drain 1412, or
both desirably are equipped with devices for controlling pressure
and flow rate of liquid as, for example, a throttling valve 1414
and a pressure gauge 1416 on the connection between the second
lumen and the drain. The operating apparatus further includes a gas
supply 1418 connected to the third peripheral lumen 1320, and a
source 1419 of a contrast medium arranged for connection to the
central lumen 1312. The operating apparatus also includes an
ultrasonic actuator 1420 arranged to apply electrical energy at an
ultrasonic frequency through the coaxial cable. The catheter has
appropriate fittings (not shown) at its proximal end 1301 for
making the connections to the operating apparatus. Typically, the
catheter is provided as a disposable unit, whereas some or all of
the elements of the operating apparatus are provided as a reusable
unit.
[0101] Prior to insertion into a patient, the catheter and
associated elements desirably are tested by actuating the liquid
supply 1410 to pass the liquid through the first peripheral lumen
and into the structural balloon 1306. Although some of the liquid
will pass out of the structure balloon through the second
peripheral lumen 1318, there is sufficient resistance to flow
provided by the second lumen as well as throttling valve 1414 that
the structure balloon fully inflates. As the balloon structure
inflates, the structural balloon expands radially and contracts
axially, causing the distal end of the balloon and the distal end
fitting 1388 to move rearwardly or proximally toward the emitter
assembly 1322, thereby compressing spring 1406. Moreover, the
balloon untwists, causing the distal end fitting 1388 to rotate
relative to the emitter structure 1322 about a central forward to
rearward axis 1426. This twists the spring 1406 about axis 1426.
Distal reinforcing tube 1396 slides rearwardly or proximally over
the proximal reinforcing tube 1400, whereas the extensible tube
1394 collapses axially.
[0102] In the fully inflated condition (FIG. 23), the reinforcing
tubes and associated elements are in an engaged condition. In this
engaged condition, distal reinforcing tube 1396 almost entirely
encompasses the proximal reinforcing tube 1400. The tubes nested in
this manner are quite rigid. The reinforcing tubes span a
substantially shorter length in this condition, and structurally
reinforce one another over substantially their entire lengths. In
the engaged condition, any angular displacement permitted by the
mutual clearance between the exterior of the proximal tube and the
interior of the distal tube is minimized. Additionally, in the
engaged condition, the proximal end of distal reinforcing tube
1396, is firmly engaged in the tapered, conical seat 1362 of the
distal mounting structure 1328 on the emitter assembly 1322. This
locks the telescoped tubes firmly in position relative to the
emitter assembly. In this condition, the reinforcing structure 1321
including the extensible structure 1392 and emitter assembly 1322
is substantially rigid. This rigid structure 1321 is connected to
the forward or distal end of the expansible balloon structure by a
distal end fitting 1388 and is also connected to the expansible
balloon structure adjacent the proximal end of the structural
balloon 1306 (FIG. 14) and the adjacent regions of the catheter
1302. In this engaged condition, the distal or forward end of the
expansible structure is rigidly held relative to the proximal end
of the expansible balloon structure and relative to the emitter
assembly.
[0103] The flowing liquid passes from the first peripheral lumen
through the first channel 1340 of the proximal mounting structure
and into the annular passageway 1376 inside the piezoelectric
element. The fluid passes from passageway 1376 through the slots
1354 in the distal mounting structure 1328 into the interior of the
structure balloon 1306. The fluid circulates through the interior
of the structural balloon and passes out of the structural balloon
port 1346, a second channel 1342 of the proximal mounting structure
1324 and the second peripheral lumen 1318. This process is
continued for a sufficient time to sweep out air or other gases
inside the structural balloon. Gas supply 1418 desirably is
actuated to inflate reflector balloon 1304 with a gas.
[0104] While the balloon structure is in its inflated condition,
the ultrasonic actuator 1420 is operated to supply electrical
energy to ultrasonic element 1326 by way of the coaxial cable 1380
(FIGS. 19 and 20). This allows a final test of the electrical
connections and piezoelectric element. The ultrasonic actuator 1420
should supply the electrical energy at a frequency precisely
matched to the resonant of frequency of the piezoelectric element
1326. Different piezoelectric elements incorporated carried by
different catheters will have slightly different resonant
frequencies. The resonant frequency of the piezoelectric element
1326 may also vary depending upon the loading applied to it by the
balloon structure, including the liquid within the structural
balloon, as well as loading applied by structures external to the
balloon structure. Preferably, the ultrasonic actuator 1420
includes a circuit (not shown) for monitoring electrical power
reflected back from the ultrasonic actuator, as well as a frequency
adjusting circuit, which is desirably arranged to vary the
frequency of the applied electrical energy until the ratio of
reflected power to apply the power is at a minimum. The
frequency-varying circuit may operate automatically in response to
a measure of the measured reflected power and a measure of the
applied power. Alternatively, the frequency-varying circuit can be
manually controlled in response to the same parameters. To simulate
the loading that will be applied during use, the balloon structure
desirably is immersed in a bath of an aqueous liquid during test
operation. Thus, during test operation the actuator 1420 is
adjusted to a frequency that closely matches the actual resonant
frequency of piezoelectric element 1326 during use. After testing,
the balloon structure is returned to its deflated condition. Any
residual spaces inside the structural balloon are completely filled
by substantially gas-free liquid.
[0105] After testing, the distal end of the catheter is advanced
through the patient's vascular system, with the balloon structure
in the collapsed or deflated condition, so as to position the
ablation device within a chamber of the patient's heart. The
flexibility of the device in the deflated condition, and the
relatively small diameter of the device, facilitates this process.
A guide wire (not shown) can be inserted through the continuous
passageway and through the distal outlet port 1390 during this
process. The guide wire may be removed after ablation device is
advanced into the heart chamber.
[0106] Once the catheter is located in the heart chamber, the
balloon structure is brought to its inflated condition by operating
the liquid supply and liquid drain as discussed above to inflate
the structural balloon 1306 and actuating the gas supply 1418 to
inflate the reflector balloon 1304. As discussed above, the
interface between the liquid-filled structure balloon 1306 and
gas-filled reflector balloon 1304 is configured so as to focus
ultrasonic waves emitted from piezoelectric element 1326 into an
annular or ring-like ablation region A (FIG. 14) coaxial with the
central axis 1426. That is, the interface directs the ultrasonic
waves so that the energy converges into this ablation region.
Stated another way, the ultrasonic intensity or (the power applied
per unit area onto a plane perpendicular to the direction of
propagation of the energy) is at a local maximum within the
ablation region A. Thus, if one were to measure the energy
intensity at various points along the direction of propagation D of
the ultrasonic waves in the vicinity of the ablation region, such
intensity would increase in the direction of propagation D of the
energy inside structural balloon 1306 and over the distance, if
any, from the structural balloon to the ablation region. The
intensity would reach a local maximum within the ablation region A,
and would progressively decrease with further travel in direction D
away from the balloon assembly. At any point around the
circumference of the ring-like focal region, the direction of
propagation D has a component in the forward direction, parallel to
axis 1426.
[0107] To provide proper focusing action, it is important to
maintain the ultrasonic emitter assembly 1322 and particularly the
piezoelectric element 1326 concentric with the structural balloon
and particularly with the interface with the structural balloon and
the reflector balloon. The rigid reinforcing structure 1321 serves
to maintain such concentricity. The ring-like ablation region A is
thus maintained in a well-defined, substantially unchanging spatial
relationship with the ultrasonic emitter assembly 1322 and other
components of the reinforcing structure and with the central axis
1426.
[0108] By manipulating the pull wire 1385 and the catheter, the
physician can position the ablation device, including the balloons
and ultrasonic emitter in a desired position relative to the heart
chamber. The physician can cause the rigid reinforcing structure,
including the emitter assembly 1322 and extensible element 1392 to
turn and thus swing axis 1426. This turning motion is accompanied
by bending of those portions of catheter 1302 near the distal end
of the catheter. Because the pull wire is connected to the rigid
reinforcing structure itself, at a point inside of the expansible
balloon structure, the balloon structure and the reinforcing
structure tend to pivot about a pivot axis schematically indicated
at 1430 (FIG. 14) close to the proximal end of the expansible
structure or actually inside of the expansible structure. This
facilitates positioning of the expansible structure. Only a
relatively limited length, from the pivot axis to the forward or
distal end of the expansible structure (at distal end fitting 1388)
needs to swing inside the limited space within the heart chamber.
By contrast, in an otherwise comparable device where the pull wire
is affixed to catheter proximal to the expansible structure, the
expansible structure will tend to swing about a pivot axis further
to the rear and hence further from the distal end of the expansible
structure.
[0109] Also, because the pull wire is attached to the emitter
assembly, it provides an additional safety feature. In the event of
a structural failure in the catheter or balloons, the emitter
assembly and those portions of the catheter and balloons remaining
attached to the emitter assembly can be retrieved from within the
patient's heart by pulling the pull wire or, in the alternative,
can be kept in place by holding the pull wire until the same can be
surgically removed in an emergency open-heart procedure. Further,
the distal end fitting 1388 is connected to the emitter assembly by
the welded spring 1406 and by the interlocked flanges 1397 and 1401
on the reinforcing tubes 1396 and 1400 (FIG. 22A). Thus, despite
the failure of any other structural elements, distal end fitting
1388 remains securely attached to the pull wire by the welded
spring 1392 and the bonded components of the emitter assembly
1322.
[0110] In the manner discussed above, the physician can rotate the
catheter and thus rotate the expansible structure and the pivot
axis 1430 about the central axis 1426. Therefore, by adjusting the
pull wire and rotating the catheter, the physician can bring the
expansible structure and the central axis to essentially any
desired orientation and location within the heart. Here again, the
position of the expansible structure can be monitored by the
physician using a contrast medium injected from contrast medium
supply 1419 (FIG. 14). To form a lesion in the form of a complete
loop or a substantial portion of a loop, the physician will bring
the apparatus to an orientation similar to that shown in FIG. 1,
referred to herein as a "normal" disposition. In this normal
distribution, at least a substantial portion of the ring-like
ablation region A is disposed within or in close proximity to the
wall of the heart. The orientation of the axis 1426 and ablation
region A are depicted schematically in FIG. 24. In the normal
disposition, the plane of the ablation region A is substantially
parallel to a plane P defined by that portion of the heart wall
lying closest to the ablation region. Thus, most or all of the
ablation region A lies within or close to the heart wall. The
physician can operate the ultrasonic actuator 1420 (FIG. 14) so as
to excite the piezoelectric element and cause the device to emit
ultrasonic waves and ablate a loop-like lesion L in the heart wall,
encompassing all or a substantial portion of a loop extending
around the axis 1426. As mentioned above, such a loop-like lesion
can be formed around the ostium OS of a pulmonary vein or around
another anatomical structure.
[0111] Alternatively or additionally, the physician may bring the
ablation device to a canted disposition, also schematically
depicted in FIG. 24. In the canted disposition, the plane of the
ring-like ablation region is not parallel to a theoretical plane
P', defined by that portion of the heart wall tissue closest to the
ablation region. In such canted disposition, the axis 1426 of the
ablation device is not perpendicular to the theoretical plane, but
instead lies at another angle, to this theoretical plane, most
typically an oblique angle. In this canted disposition, ablation
region A1 is close to or within the heart wall over only a small
portion of the circumference of the ablation region. If the
physician actuates the ultrasonic actuation source and causes the
ablation device to emit ultrasonic waves while the device is in
this canted disposition, ultrasonic waves will again be focused in
the entirety of the ablation or focal region A. However, ablation
will occur only where the ablation or focal region A is within or
in close proximity to the heart wall. Thus, a lesion L' will be
formed only along a relatively small arcuate region approximating a
straight line.
[0112] The energy directed into other portions of the ablation
region A', which lie remote from the heart wall, will pass
forwardly, in propagation directions D. The stray ultrasonic waves
will pass into the blood within the heart. However, the intensity
of the ultrasonic waves diminishes rapidly with distance in the
propagation direction, beyond the ablation focal region A'.
Moreover, the ultrasonic absorptivity of blood is relatively low,
and the blood within the heart is typically moving and is thermally
conductive. Therefore, the ultrasonic waves passing into the blood
typically will not heat the blood to a degree sufficient to cause
coagulation. Some of the ultrasonic waves passing in the forward
direction, beyond the ablation region A, may impinge on portions of
the heart wall remote from the ablation region. However, because
the ultrasonic intensity diminishes with distance in the forward
direction, those portions of the heart wall remote from the
ablation region A' typically will not be heated to a degree
sufficient to cause unintended ablation of those regions.
[0113] During the course of a treatment, the physician can use the
normal and canted dispositions as desired, and in any order.
Because the disposition of the ablation device is established
without reliance on engagement between the device and the pulmonary
vein ostium or other anatomical structures, the loop-like and
linear lesions can be placed where desired. It has been proposed
that atrial fibrillation can be treated successfully by forming
lesions surrounding the ostia of the pulmonary veins in combination
with linear lesions. Such a combination of lesions can be achieved
by use of the canted and normal dispositions. Preferably, the
ablation device is moved between dispositions while the expanded
structure remains in its expanded condition. Thus, where the
expansible structure includes balloons, as discussed above, the
balloons remain inflated while the device is maneuvered. Once
again, the ability to inject contrast medium while the balloons
remain in their inflated condition, and without using a separate
catheter for such introduction, is advantageous.
[0114] When the piezoelectric element is actuated to emit
ultrasonic waves, it will also generate heat. Preferably, the
liquid supply 1410 (FIG. 1) and liquid drain 1412 are operated to
continually circulate the aqueous liquid through the ablation
device. As mentioned above in connection with the initial inflation
of the structural balloon, the aqueous liquid passes from the
supply 1410 through first side lumen 1316 of the catheter, through
the first channel 1340 of the proximal mounting structure and into
the annular channel 1376 (FIGS. 20 and 21) within the piezoelectric
element 1326. The fluid passing within the piezoelectric element
passes through the channels 1354 of the distal mounting element,
into the structural balloon 1306 and ultimately passes out of the
structural balloon through port 1346 (FIG. 21), second channel 1342
of the proximal mounting structure and the second peripheral lumen
1318 of the catheter, whereupon it passes to the drain. This
circulation is achieved without need for a separate catheter for
liquid circulation and without occupying the central lumen of the
catheter with the circulating liquid. The circulating liquid
effectively removes heat from the piezoelectric element.
[0115] As mentioned above, both the first channel 1340 and the
second channel 1342 communicate with the annular channel 1376
inside the piezoelectric element. Therefore, some portion of the
circulating liquid may pass from the proximal end of the annular
channel back into the second channel 1342 and to the drain, without
passing through the entire annular channel. However, this effect is
minimal. In a variant, a blocking wall (not shown) can be provided
so as to close the second channel distal to port 1346. Such a
blocking wall may be formed integrally with the proximal mounting
structure 1324, as a part of the piezoelectric element or as a
separate element inserted between the piezoelectric element and the
proximal mounting structure.
[0116] Numerous variations and combinations of the features
discussed above can be employed. For example, in the variant
depicted in FIGS. 25 and 26, the extensible structure 1492 includes
a reinforcing tube 1496 which can be telescopically received inside
the emitter assembly 1322' when the expansible structure is in its
expanded condition, as when the structural balloon 1306' is in its
inflated condition (FIG. 26). In the particular structure
illustrated, the reinforcing tube 1496 fits through the bore 1450
of the distal mounting structure of the emitter assembly and is
telescopically received within the inside tube 1370. When the
expansible structure is collapsed, and hence balloon 1306' is
deflated, the reinforcing tube 1496 is partially or fully withdrawn
from the inside tube 1370', from bore 1450, or both. Here again,
the structure provides reinforcement against kinking, but allows
flexibility in the deflated, extended condition and also cooperates
with the emitter assembly, so as to form a passageway extending
through the expandable balloon structure.
[0117] Other extensible structures are disclosed in co-pending PCT
International Application No. PCT/US03/28578 and the corresponding
co-pending U.S. patent application Ser. No. 10/635,170, published
as US/2004/0054362-A1 and granted as U.S. Pat. No. 6,808,524, the
disclosure of which is incorporated by reference herein, as well as
in the '257 application. The preferred extensible structures in
these applications include engagement elements which reinforce the
expansible structure and form a rigid structure when the expansible
structure is in its expanded condition. In one arrangement, the
engagement elements include a tubular distal engagement element
which extends proximally from the distal end of the expansible
structure or balloon. A coil spring is disposed inside of this
tubular engagement element. A proximal engagement element includes
a main portion, a stem having a diameter smaller than the diameter
of the main portion and a bulbous tip at the proximal end of the
stem. The bulbous tip is engaged inside the distal engagement
element at all times. When the expansible structure is in its
collapsed condition and the extensible structure is in its extended
condition, only the bulbous tip remains engaged inside the distal
engagement element. In this disengaged condition, the distal
engagement element can pivot around the bulbous portion of the stem
so that the structure can flex. When the expansible structure is
expanded, the distal element is forced proximally, so that the main
portion of the proximal element enters into the distal element and
the distal element is forced to a coaxial alignment with the
proximal element. In this engaged condition, the elements form a
rigid reinforcing structure. An extensible tube may extend from the
proximal element through the interior of the coil spring, so as to
provide a continuous passageway for the purposes discussed above
herein. In a variant of this structure according to a feature of
the present invention, the engagement elements may be provided with
interlocking features such as an inwardly-projecting flange on the
distal engagement element having a diameter slightly smaller than
the diameter of the bulbous tip. Such a flange prevents the distal
engagement element from moving distally beyond the bulbous tip on
the proximal engagement element, and thus serves the same function
as the interlocking flanges 1397 and 1401 discussed above with
reference to FIG. 22A.
[0118] The structures which provide for circulation of the cooling
liquid may be varied. Merely by way of example, the port 1346
(FIGS. 15 and 16) of the proximal mounting structure may be
replaced by one or more slots similar to the slots 1354 (FIG. 17)
in the distal mounting structure. Conversely, the slots of the
distal mounting structure may be replaced by a port, as used in the
proximal mounting structure discussed above. Also, it is not
essential that the second peripheral lumen of the catheter
communicate with the interior of the structural balloon through a
feature of the proximal mounting structure. For example, where the
distal end of the catheter projects into the interior of the
structural balloon, the catheter itself may be provided with a port
or slots to provide communication with the second lumen. In a
further variant, one or both of the mounting structures may be
omitted. For example, the proximal mounting structure may be
omitted if the distal end of the catheter itself incorporates a
port. In such an arrangement, one of the additional lumens of the
catheter may communicate directly with the interior of the tubular
piezoelectric element, whereas another additional lumen of the
catheter may communicate directly with the interior of the
structural balloon. Also, although it is highly advantageous to
have a continuous passageway extending through the ablation device
in its expanded condition, the same can be omitted as, for example
where it is acceptable to use a separate catheter for injection of
the contrast medium. Also, although the reinforcing structure 1321
discussed above provides important advantageous in stiffening the
expansible structure and assuring the ablation region lies in a
predictable location, the same can be omitted with corresponding
loss of function.
[0119] In the embodiment discussed above with reference to FIGS.
14-23, the interface between the inside tube 1370 and the liquid in
the annular passageway 1376 has some reflectivity for ultrasound,
so that at least some of the ultrasonic waves directed radially
inwardly from the inside surface of the tubular piezoelectric
element will be reflected at this interface and directed radially
outwardly to reinforce the useful ultrasonic waves emitted at the
outside surface of the piezoelectric element. As disclosed in the
aforementioned '512 publication, and as further described in U.S.
Patent Publication US 2003/0013968 A1, the disclosure of which is
hereby incorporated by reference herein, a highly reflective
interface may be provided by forming a tube as a dual-walled
structure with an gas-filled space between the walls.
[0120] Further, certain features of the embodiments discussed
above, as, for example, the use of a normal and canted disposition,
can be applied with ablation devices which use forms of energy
other than ultrasonic as, for example, ablation devices which apply
light, radio frequency or other forms of energy.
[0121] In apparatus according to a further embodiment of the
invention, (FIG. 27), the insertable structure may incorporate a
guide element 701 adapted to engage a portion of the anatomy as,
for example, the ostium of the pulmonary vein, distal to or forward
of the ablation device 718. The guide element may be linked to the
ablation device by a bendable or deformable element 703 which can
be deformed in any of the ways discussed above with reference to
deforming the catheter, so that the disposition of the ablation
device relative to the heart wall W may be controlled as, for
example, by bending the link 703 to the position indicated in
broken lines at position 703', so as to move the ablation device to
the position indicated in broken lines at 718'. The guide element
701 or the link 703 may be provided with a port for emitting a
contrast medium in the manner discussed above.
[0122] In yet another variant, one or more independently inflatable
structures 705 may be provided on the distal or forward surface of
the ablation unit itself, so that the ablation element may be
tilted relative to the heart wall and positioned relative to the
heart by inflating one or more of the inflatable structures, as
indicated at 705'. These additional inflatable structures can be
positioned in a region of the distal wall which will bear on the
wall of the heart or other anatomical structure, but which does not
serve to transmit appreciable amounts of the ultrasonic waves from
the reflective interface to the heart wall. Alternatively, the
additional reflective structures 705 may be liquid-inflatable
balloons which are adapted to transmit the ultrasonic waves so that
the ultrasonic waves can be transmitted through these
structures.
[0123] As discussed above, the ablation device can be positioned
selectively within the heart and brought to the desired disposition
relative to the heart wall regardless of the configuration of the
ostium and pulmonary vein. This enhances the ability of the device
to form a loop-like ablated region within the heart wall
surrounding the pulmonary vein.
[0124] Additionally, an ablation device which focuses the
ultrasonic waves into a relatively large loop-like region having a
loop diameter D.sub.A (FIG. 1) of about 25 mm or more, and
preferably about 25-30 mm, also tends to provide better results
than a device forming a smaller-diameter ablation region as, for
example, about 20 mm. While the smaller loop diameters as, for
example, 20 mm or so, provide a loop diameter sufficient to
encompass the ostium in some subjects, the use of loop diameters
within the preferred range increases the probability that the loop
diameter will be sufficient to encompass the ostium, even where the
subject has a widely flared or noncircular ostium or other a
typical shape. Significantly larger loop diameters require
significantly larger balloon diameters, which make the task of
threading the device into the heart and removing it from the heart
more difficult.
[0125] A loop diameter of about 30 mm can be provided using an
ablation unit with a structural balloon of about 32 mm maximum
diameter in the inflated condition. One example of a suitable
structural balloon is depicted in FIG. 39 with exemplary dimensions
as shown in Table I, below. This balloon has a "nipple" or
projection 731 on its distal side, which can be engaged with the
ostium of the pulmonary vein during positioning. Such a nipple can
be used in conjunction with the other positioning systems discussed
herein. However, where a steering system is provided for
controlling the disposition of the ablation device, it is desirable
to omit the nipple and to make the balloons and associated
structures as short as practicable in the proximal-to-distal or
forward-to-rearward dimension. For example, one suitable structural
balloon which provides a 25 mm loop diameter has a maximum diameter
of 28 mm in the inflated condition, and has a length of only 26 mm.
This balloon does not have a nipple.
TABLE-US-00001 TABLE I Dimension Indicator Dimension Name (FIG. 39)
Value Balloon length (LB) 35.0000 mm Balloon radius (RB) 16.0000 mm
Lumen radius (RL) 1.6890 mm Parabola focus height (PFH) 27.0000 mm
Parabola focus radius (PFR) 15.0000 mm Parabola zero (PZ) 2.4600 mm
Transducer height (HT) 9.0000 mm Nipple section length (LN) 1.3700
mm Nipple radius (RN) 5.0000 mm Nipple angle (AN) 52.3200 degree
Fillet #1 radius (RF1) 1.6700 mm Fillet #2 radius (RF2) 5.7900 mm
Fillet #3 radius (RF3) 5.7900 mm Fillet #4 radius (RF4) 3.0000 mm
Fillet #5 radius (RF5) 5.0000 mm Fillet #6 radius (RF6) 2.0000
mm
[0126] As seen in FIG. 28, the loop diameter D.sub.A can be
increased by directing the ultrasonic waves from emitter 823
rearwardly, as well as radially outwardly away from axis 826. Such
rearward direction may be provided by an emitting element 823 in a
conical or other shape having a circumferential wall 821 which
slopes outwardly, away from the central axis 826 in the forward
direction. The rearwardly directed ultrasonic waves impinge on the
active reflective surface 824 and are reflected outwardly, away
from the axis to a greater degree than would be the case for purely
radially-directed ultrasonic waves. Thus, the ratio of the loop
diameter D.sub.A of the ablation region A to the diameter D.sub.B
of balloon or other structure providing the reflective interface
can be increased.
[0127] In a further variant, the rearwardly and outwardly directed
ultrasonic waves can be provided by a cylindrical emitter
configured as a series of cylindrical bands spaced along the axis
and operated as a phased array.
[0128] In a further variant depicted in FIG. 29, a cylindrical
transducer 840 having a central axis 846 may be equipped with an
annular Fresnel lens 842 coaxial with the transducer. The lens is
formed from a material such as a solid polymer, metal, ceramic or
the like in which the speed of sound is greater than the speed of
sound in the liquid 844 used to fill the balloon surrounding the
transducer. The Fresnel lens includes a series of annular rings 846
each having a relatively thick portion 848 at its distal edge and a
relatively thin portion 850 at its proximal edge. As shown in
detail in the sectional view of FIG. 30, an ultrasonic wave 852
traveling from the surface 854 of transducer 840 through the thick
portion 848 of a ring traverses a relatively long distance through
the material of the lens and a relatively short distance through
the liquid 844 to reach a location 858 beyond the lens, at a given
radial distance from the central axis of the transducer.
Conversely, a wave 856 traveling through a thin portion of the ring
travels through a relatively short distance in the material of the
lens and through a relatively long distance in liquid 844 to reach
the same radial location 858. The two waves start from surface 854
in phase with one another. When they reach radial location 858,
wave 852 is advanced in phase relative to wave 856 so that the two
waves merge to form a combined wave 860 directed rearwardly. The
rearwardly directed waves 860 can be reflected as described
above.
[0129] The Fresnel lens can be varied in numerous ways. For
example, it is not essential to have the Fresnel lens in contact
with the surface of the transducer. Also, the rings constituting
the lens need not contact one another and indeed can be spaced
apart from one another so that regions between the spaced rings
constitute portions of the lens with zero thickness. Also, the
rings can be replaced by successive terms of a helix 870 (FIG. 31)
coaxial with the transducer. At each location around the
circumference of the cylindrical transducer, adjacent turns of the
helix act in the same way as adjacent rings. The helix desirably
has non-uniform thickness in the axial direction, so that each turn
of the helix has a relatively thick portion 878 at the distal edge
of the turn and a relatively thin portion 880 towards the proximal
edge of the turn. In a further variant (not shown) a helix having
spaced apart turns or a lens formed from spaced apart rings may
have rings or turns of uniform thickness, so that the lens is
formed solely by portions having zero thickness (portions between
rings or turns) and portions of a given, uniform thickness. Such a
lens will diffract a portion of the ultrasound in the rearward
direction and a portion of equal strength in the forward direction.
The diffraction or ultrasound-directing properties of an annular
Fresnel lens defined by spaced-apart rings or by the turns of a
helix can be varied by changing the spacing between the turns or
rings as, for example, by compressing or stretching the helix 870.
Annular Fresnel lenses as discussed above can be used in connection
with reflective or other focusing elements as in the combinations
above or can be used independently as, for example, to project a
collimated, generally conical beam of ultrasound around the axis
the transducer.
[0130] In a further embodiment, shown in FIG. 33, the transducer
951 is disposed within a structural balloon 955, which again is
filled with a liquid and directs ultrasonic waves outwardly to a
first reflective interface formed by a wall separating the interior
of the structural balloon from the interior of a reflective balloon
957, which is filled with a gas. The shape of the reflective
interface 953 is selected so that the reflected ultrasound is
directed forwardly or distally and radially inwardly to a second
reflective interface 961 defined by the liquid filled structural
balloon 955 and a gas-filled auxiliary reflector balloon 963. The
ultrasound is reflected forwardly and radially outwardly at
interface 961. Most preferably, the second reflective interface 961
is configured as a hyperboloid of revolution about the central axis
965 of the device. That is, surface defining second reflecting
interface 961 has a generatrix defined by the equation
(X.sup.2/A.sup.2)-(Y.sup.2/B.sup.2)=1 where A and B are constant; X
is distance from an axis 967 and Y is axial distance from an origin
point along an axis 967 disposed at an oblique angle to the central
axis of the balloon structure. The generatrix is the curve which,
when rotated around the central axis 965 of the emitter, forms the
surface. The hyperboloid further focuses the ultrasonic waves as
well as reflecting them outwardly into an ablation region A. For
example, where the first reflective interface 953 is arranged to
focus the ultrasonic waves at a point 981 on the central axis 965,
the second reflective interface 961 refocuses the energy to an
annular focal region in the ring-like ablation zone A. The use of
an auxiliary reflective balloon tends to "throw" via ultrasound
outwardly and thus aids in forming an ablation region A, having a
larger diameter D.sub.A using a reflective structure having the
relatively small balloon diameter D.sub.B.
[0131] As seen in FIG. 32, a reflective surface 924 such as that
defined by a common wall between balloons 922 and 920 may be
provided as a series of multiple reflective regions 923 and 925
distributed in the axial or forward-to-rearward direction. The
emitter 901 may be moved forwardly and rearwardly so as to
selectively direct the ultrasonic waves onto one or another of
these regions and thereby direct the ultrasonic waves into a first
loop-like region A, shown in solid lines, or onto a second region
A' of larger diameter, shown in broken lines. Alternatively, an
elongated emitter may be provided in two independently actuatable
zones so that when one zone is actuated, the energy is directed
onto region 923; whereas when another zone is actuated, the energy
is directed onto region 925 of the reflective surface. This
arrangement provides for selection of loop diameters during
use.
[0132] In the arrangements discussed above, the ultrasonic waves
are directed generally forwardly in a direction from the interior
of the heart toward the pulmonary vein or other blood vessel to be
circumscribed by the ablation region. In the variant shown in FIG.
34, the ablation device 1018 is configured to direct ultrasonic
waves rearwardly, in the direction from the blood vessel toward the
heart and onto a ring-like region of the heart wall W encircling
the pulmonary vein PV or ostium OS.
[0133] For example, the ablation structures discussed herein can be
adapted to direct to the ultrasonic waves rearwardly by reversing
the distal and proximal ends of such structures.
[0134] An ablation element (FIG. 35) in accordance with a further
embodiment of the invention includes transducer 1102 and a balloon
structure defining a first reflective interface 1104 and a second
reflective interface 1106 spaced apart from the first reflective
interface. The first and second reflective interfaces are both in
the form of surfaces of revolution about the central axis of 1108.
As in the embodiments discussed above, the first reflective
interface 1104 may be formed by an interface between a structural
balloon 1110 and a first reflective balloon 1112, the structural
balloon being filled with a liquid such as an aqueous liquid and
the first reflective balloon being filled with a gas. The second
reflective interface 1106 may be formed by an interface between the
structural balloon 1110 and a second reflector balloon 1114, also
filled with a gas. The two reflective interfaces converge with one
another, but do not meet, so that there is a small portion of the
wall of the structural balloon forms an exit window 1114, extending
around the central axis 1108. The second reflective interface 1106
may be in the form of a surface of revolution of an exponential
curve such that the radial distance R.sub.1108 from the central
axis 1108 any point on the curve is equal to e.sup.z+C where z is
the axial distance from an origin point to the point on the surface
1106 and C is a constant. The first reflective interface 1104
slopes forwardly and radially outwardly; it may be in the form of a
cone or other surface of revolution about central axis 1108. The
converging reflective interfaces define an annular channel 1151
having an entry 1153 surrounding transducer 1102 and an annular
exit at window 1114. The reflective interfaces 1104 and 1102
converge with one another toward the exit of the channel, and
concentrate sound waves emanating from transducer 1102 into a small
area as the sound waves pass from the transducer to exit window
1114. Thus, sound waves passing outwardly from the transducer or
repeatedly reflected between the two interfaces so that they
ultimately reach the exit window. The converging interfaces, thus
concentrate the ultrasonic waves into a small band of ultrasonic
waves exiting through the exiting window 1114 into the ablation
region. Convergent surfaces other than exponential and conical
surfaces can be used.
[0135] Depending upon the exact configuration of the converging
surfaces will direct the ultrasonic waves exiting through the
window outwardly and forwardly. The device shown in FIG. 35 directs
the ultrasonic waves nearly radially, outwardly. However, as shown
in FIG. 36, where the exit window 1114' forms a portion of the
distal wall of the ablation device and where the converging
reflective services 1106' and 1104' are oriented closer to parallel
with a forward to rearward axis 1108' of the device, the ultrasonic
waves will be directed substantially forwardly so as to ablate
region A1 almost directly in front of the device. In a variant of
the structures shown in FIGS. 22 and 23, the structural balloon
1110 of FIG. 35 is omitted and the exit window at 1114 is simply
left open to the surroundings. The space within the channel
surrounding the transducer is filled with blood or other bodily
fluids or by an anatomically-compatible fluid introduced into the
area surrounding the transducer as, for example, saline
solution.
[0136] The concept of a sonic or ultrasonic concentrator defined at
least in part by gas-filled structures forming reflective
interfaces is not limited to ablation of ring-like region. For
example, as seen as FIG. 37 an elongated catheter 1200 has
gas-filled regions 1202 and 1204 and a liquid-filled region 1206
extending lengthwise along the catheter. Gas-filled region 1202
defines a first reflective interface 1208 with the liquid-filled
region whereas gas-filled region 1204 defines a second reflective
interface 1210 with the liquid-filled region. These reflective
interfaces converge with one another but do not meet one another,
so that a portion of the liquid-filled region disposed between the
converging interfaces extends to the exterior of the catheter and
defines an exit window 1212. Thus, the reflective interfaces define
a channel 1251 having a wide entry 1253 and a narrow exit at window
1212. The exit window is generally in the form of a strip or slit
extending lengthwise along the catheter. A planar, slab like
transducer 1214 also extends lengthwise along the catheter. As seen
in FIG. 37, ultrasonic waves directed from the face of the planar
transducer impinge on the reflective interfaces 1208 and 1210 and
is repeatedly reflected by the interfaces so that the ultrasonic
energy is concentrated into the slit-like exit window. Such a
structure can be used, for example, to ablate a strip-like region
of tissue.
[0137] In yet another embodiment, an elongated catheter 1300 (FIG.
38) includes a central lumen 1302 filled with a liquid. The
catheter includes an outer sheath 1304 surrounding the central
lumen and defining an annular space 1306 between the wall 1308 of
the central lumen and the exterior of the catheter. The space 1306
is filled with a gas so as to define a single tubular reflective
interface at the wall 1308 of the central lumen, forming a tubular
channel. Such a catheter serves as a flexible wave guide for
ultrasonic waves. The reflective interface 1308 may also define a
convergent horn-like structure 1310 at the proximal or entry end of
the wave guide. Ultrasonic waves from a transducer 1312 is
concentrated by the convergent horn and travels through the wave
guide to an exit opening 1314 at the distal end of the
structure.
[0138] As discussed above, in ablation of the heart wall for
treatment of atrial fibrillation, the ablation region desirably
extends through the heart wall, rather than through the wall of the
pulmonary vein. However, the ablation region may extend in the
ostium or even through a proximal region of the pulmonary vein.
However, it is preferred to keep the ablation region out of the
pulmonary vein and at as large a diameter as possible, so as to
minimize scarring and stenosis of the pulmonary vein. Imaging
modalities other than fluoroscopy can be used, such as conventional
x-ray imaging, CT or MR imaging. Also, contrast media other than
x-ray contrast media can be employed. Ultrasonic ablation devices
other than the specific balloon structures discussed above can be
used. Also, the techniques can be used with non-ultrasonic ablation
devices.
[0139] As discussed in the aforementioned co-pending applications,
the techniques used for pulmonary vein ablation also can be applied
to ablation of other anatomical structures for other therapeutic
purposes.
[0140] As these and other variations and combinations of the
features discussed above can be utilized without departing from the
present invention as defined by the claims, the foregoing
description of the preferred embodiment should be taken by way of
illustration rather than by way of limitation of the invention.
* * * * *