Patent Application
20050027289
The entire disclosures of each of U.S. Pat. No. 6,035,657, issued Mar. 14, 2000 for a FLEXIBLE CATHETER CRYOSURGICAL SYSTEM (“the '657 patent”), U.S. Pat. No. 5,910,104 issued Jun. 8, 1999 for a CRYOSURGICAL PROBE WITH DISPOSABLE SHEATH (“the '104 patent”), U.S. Pat. No. 5,275,595 issued Jan. 4, 1994 for a CRYOSURGICAL INSTRUMENT (“the '595 patent”), and U.S. patent application Ser. No. 09/872,117 (“the '117 application”), all assigned to CryoGen, Inc. of San Diego, Calif. are hereby expressly incorporated by reference in their entireties.
The present invention relates to devices and methods for the treatment of cardiac arrhythmia, and more specifically relates to devices and methods for the treatment of focal atrial arrhythmia using cryoablation.
Normal cardiac rhythm is maintained by precisely timed nerve signals conducted through cardiac tissue to electrically stimulate synchronous contractions of the four heart chambers (2 ventricles and 2 atria). In a normal rhythm, the nerve signals are typically conducted along paths initiating at the sino-atrial (SA) node and passing from there through the atrioventricular (AV) node and the bundle of His to the ventricular myocardial tissue.
Abnormal cardiac rhythms, or arrhythmias, including atrial fibrillation, are potentially dangerous medical conditions which may result from disturbances in the site of origin and/or the pathways of conduction of the nerve impulses that excite contraction of the four chambers of the heart. The site of origin and pathways of conduction of these signals are currently mapped, for example using an electrocardiograph (ECG) in conjunction with mapping methods such as those described in U.S. Pat. No. 4,641,649 to Walinsky et al.
One common type of abnormal atrial fibrillation occurs when the contraction initiating signals originate within one or more of the pulmonary veins, rather than at the SA node. These atrial arrhythmias have been treated by a variety of methods including pharmacologic treatments, highly invasive surgical procedures and linear and circumferential radio frequency (RF) ablations of the myocardial wall. However, each of these methods has drawbacks, e.g., the pain and extended recovery time for invasive surgery, relative ineffectiveness of pharmacologic treatments and restenosis at the ablation site due to the application of RF energy or other heat based therapies, and the necessity to repeat the ablation procedure to treat a sufficiently large area of tissue.
The present invention is directed to systems and methods for ablating tissue of a patient. For the present invention, the system includes a substantially rigid sheath and an elongated cryoablation catheter that defines an axis. The catheter has an ablating distal section that includes a plurality of conductive bands, with each band establishing an enclosed chamber. For the cryoablation catheter, the ablating distal section is reconfigurable between a first configuration and a second configuration. In the first configuration, each band is positioned relatively near the axis to place the ablating distal section in a relatively compact configuration for transit through the sheath. On the other hand, when the ablating distal section is in the second configuration, each band is positioned relatively far from the axis. The second configuration is useful for ablating a circumferential band of tissue, for example, a band of tissue surrounding the opening (i.e. ostium) where a pulmonary vein connects with the left atrium.
Once the ablating distal section is in the second configuration, the bands can be placed in contact with selected tissue and cooled to cryoablate the tissue. To cool the bands, a fluid refrigerant is expanded into each enclosed chamber. In greater detail, the fluid refrigerant can be passed through one or more orifices to expand the fluid and cool the bands.
In a first embodiment of the system, the ablating distal section includes a plurality of cylindrical bands that are each centered on the catheter axis. A capillary tube that is positioned along the axis is formed with one or more orifices and establishes one or more chambers between the inner surface of each band and the outer surface of the capillary tube. Refrigerant is pumped through the capillary tube for outflow into the chamber(s) through the orifice(s). In one implementation, the plurality orifices are arranged along a line that is parallel to the axis, with a proximal orifice having a relatively large diameter and a distal orifice having a relatively small diameter. The remaining orifices (i.e. the orifices between the distal and proximal orifices) have diameters that progressively decrease, from orifice to orifice, in a distal direction. This cooperation of structure is provided to maintain a constant cooling rate along the ablating distal section.
In the first, compact configuration that is useful for passing the ablative distal section through the sheath, the bands combine to form a cylinder and the capillary tube is substantially straight. On the other hand, in the second configuration, the bands combine to form a coiled structure and the capillary tube typically bends and becomes arcuate. To reconfigure the ablating distal section, a shape memory element which has an arcuate shape when unconstrained can be attached to the bands. With this cooperation of structure, the shape memory element can be deformed (e.g. elastically deformed) until it is straight or only slightly curved, placing the ablating distal section in the first, compact configuration. While the shape memory element is deformed, the ablating distal section can be inserted into and advanced through the sheath, where the sheath acts to constrain the shape memory element. When the ablating distal section exits the distal end of the sheath, the shape memory element becomes unconstrained and assumes its arcuate shape, reconfiguring the ablating distal section into the second, substantially coiled configuration. The coiled ablating distal section can then be used to cryoablate a circumferentially shaped band of tissue in a one-step process. Alternatively, a linear actuator (e.g. pull wire) having a distal end attached to the ablating distal section can be manipulated at an extracorporeal location to reconfigure the ablating distal section into a coiled configuration.
In another embodiment of the system, the ablating distal section includes a plurality of arms with each arm extending from a proximal end to a distal end and having a hinge joint therebetween. For this embodiment, a band is mounted on each arm between the arm's hinge joint and arm's distal end. A linear actuator (e.g. pull rod) is attached to the distal end of each arm to proximally retract the distal end of each arm relative to the arm's proximal end. In the first configuration, each arm is somewhat straight and the bands are typically positioned very close to the catheter axis. When the rod is pulled, each arm bends at its respective hinge joint causing each band to move radially outward from the axis. This reconfigures the ablating distal section into the second configuration suitable for cryoablating tissue.
In another embodiment, the ablating distal section includes a plurality of arms, with a band attached to the distal end of each arm. Each arm, when unconstrained, has an arcuate shape. Specifically, when unconstrained, the proximal end of each arm is positioned near the axis and the distal end of each arm deflects from the catheter axis to distance each band from the axis. With this cooperation of structure, the arms can be deformed (e.g. elastically deformed) until they are straight or only slightly curved, placing the ablating distal section in the first compact configuration. With the arms deformed, the ablating distal section can be inserted into and advanced through the sheath, with the sheath constraining the arms. When the ablating distal section is pushed out of the distal end of the sheath, the arms become unconstrained and assume their arcuate shape, reconfiguring the ablating distal section into the second, expanded configuration. With the ablating distal section expanded, the bands can be placed in contact with target tissue and cooled to cryoablate the contacted tissue.
In one application of the present invention, the distal end of the sheath is inserted into a patient's vascular system and advanced into the right atrium. The interatrial septum is then pierced and the distal end of the sheath is passed through the septum and into the left atrium. In one implementation, the distal end of the rigid sheath is then maneuvered into a position proximal to a portion of the tissue to be ablated. Next, the distal end of a cryoablation catheter having an ablating distal section, such as one of the ablating distal sections described above, is pushed through the sheath until the ablating distal section is pushed out of the distal end of the sheath. For some embodiments, the ablating distal section reconfigures into an expanded, and in some cases coiled, second configuration as the ablating distal section exits the sheath (see discussion above). For other embodiments, a linear actuator (e.g. a pull wire or pull rod) can be activated once the ablating distal section exits the sheath to reconfigure the ablating distal section into an expanded, and in some cases coiled, second configuration.
Once the ablating distal section has been placed in the second configuration, the bands are placed in contact with the tissue to be ablated and cooled. Specifically, a refrigerant is passed through the orifices in the ablating distal section to expand the refrigerant into the chamber(s) to cool the bands and contacted tissue. For example, the contacted tissue can be a circumferential band of tissue surrounding the opening (i.e. ostium) where one of the pulmonary veins connects with the left atrium.
In another implementation, the sheath is formed with a curved distal portion. The curved distal portion is advanced into the left atrium after piercing the interatrial septum. Once in the left atrium, the distal portion of the sheath is maneuvered until the distal end is facing a selected pulmonary vein opening. Next, the ablating distal section of a cryoablation catheter is passed through the sheath and into the selected opening where the pulmonary vein connects with the left atrium. The bands are then placed in contact with the tissue to be ablated and cooled.
The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which:
a are side elevation views showing an embodiment of a cryoablation catheter according to the present invention;
a are cross sectional views showing details of the embodiment shown in
The present invention may be further understood with reference to the following description and the appended drawings, wherein like elements are referred to with the same reference numerals.
In many cases, arrhythmia results from contraction initiating signals that originate within one or more of the pulmonary veins rather than from the SA node. Known techniques may be used to locate the point of origin of the aberrant signals, and their paths of conduction. Once these locations have been determined, the device and method according to the present invention may be employed to ablate a portion of tissue within the identified pulmonary vein between the source of the signals and the left atrium, e.g., near the opening or collar of the pulmonary vein, to create a circumferential conduction block within the pulmonary vein. This conduction block prevents the abnormal contraction originating signals from propagating into the left atrium to restore a normal contraction sequence.
The present method and apparatus allows for ablation of an elongated strip of tissue (e.g. a linear ablation) and can reduce the number of applications required to create the circumferential conduction block, thereby reducing the time required to complete the procedure as well as the trauma to the patient.
Catheter 102 may include a spiral portion 104 which may be shaped to match a surface of the portion of tissue to be ablated. In one exemplary embodiment, the spiral portion 104 is maintained in a straight configuration while received within the sheath, and deploys to the spiral configuration only after being pushed outside the sheath. A shape memory element 106 may urge the spiral portion 104 to assume the desired configuration once the spiral portion 104 has left the sheath and is no longer restrained thereby. Shape memory element 106 may, for example, be a stylet made of Nitinol, which can be both external or internal to the catheter 102. In an exemplary use, the catheter 102 may be straightened by a user outside of the patient, before being introduced into the sheath, and remains straight while therewithin. Once the catheter 102 has been pushed out of the distal end of the sheath, the shape memory element 106 returns to its unconstrained shape, and causes the spiral portion 104 to assume the desired shape.
The exemplary embodiment of the catheter 102 according to the present invention shown in
Cross referencing
The capillary tube 110, in the exemplary embodiment shown in
In a different exemplary embodiment according to the present invention, the cooling along the length of the ablating distal section may be balanced by providing orifices 116 having the same dimensions, each having an independent supply of refrigerant fluid. For example, as shown in
A conductive distal tip 126 may also be included in the catheter 102, located at the most distal portion of the ablating section, according to an embodiment of the invention. Tip 126 may be used to ablate pinpoint portions of tissue, or may combine with the bands 108 to cryoablate an extended band of tissue around the circumference of the pulmonary vein in a single application. As described above, the tip 126 is cooled by refrigerant fluid from the capillary tube 110 expanded through a distal-most orifice 116.
Once the arms 406 are deployed, the user advances the catheter 402 distally until the conductive bands 412 are in contact with the portion of tissue to be ablated. Cooling is initiated and maintained until the tissue adjacent to each of the conductive bands 412 is ablated. The user then allows the conductive bands 412 to return to body temperature so that they may be removed from contact with the tissue without harm thereto. If further ablation is required to complete a circumferential conduction block, the user rotates the catheter 402 around the axis thereof so that the conductive bands 412 are offset from their former positions, and the process is repeated until the circumferential conduction block is complete. Then, when the operation has been completed, the arms 406 may be returned to the collapsed configuration by simply withdrawing the catheter 402 into the sheath 400 or by extending rod 407 distally.
As would be understood by those of skill in the art, the arms 406 may alternatively be deployed to the operative position by a stylet as described above, or by a different mechanism that may include shape memory and/or resilient elements as would be understood by those of skill in the art. As shown in
The exemplary embodiment shown in
An ablation element 600 according to a further embodiment of the invention shown in
As described above, an outer surface 606 of the ablation element 600 may be formed of, for example, copper or another thermally conductive material. The outer surface 606 is cooled by the refrigerant fluid expanding within the chamber 616 to provide a substantially uniformly cooled cryoablation surface for ablating tissue. In one exemplary embodiment, an additional orifice 618 may be provided at a distal end of the capillary tube 602 to cool a distal tip 608 of the ablation element 600. This allows a user to ablate specific points of tissue by applying the distal tip 608 thereto. Furthermore, the outer surface 606 may have a thermally insulating coating applied to predetermined portions thereof so that the cooling effect is substantially directed toward that portion of the outer surface 606 which is to contact the tissue to be ablated. For example, a coating of Pebax™ may be applied by RF fusion techniques to surfaces facing away from the orifices 604. Alternatively, an insulating cover may be provided to surround selected portions of the ablation element 600 while leaving the tissue contacting portions of the outer surface 606 exposed. That is, as with the insulative coating described above, the insulating cover may cover parts of the ablation element 600 that are not intended to contact the tissue to be ablated. Thus, the insulating cover 610 concentrates the cooling effect of the expanding refrigerant fluid at the tissue contacting portions of the ablation element 600 thereby reducing the amount of cooling required. Furthermore, those of skill in the art will understand that an insulative coating or cover as described herein may also be employed in any of the previously described catheter-based embodiments.
Thereafter, the Brockenbrough needle 730 is retracted into the dilator 728 and removed from the body. The rigid sheath 722 is then advanced along the dilator 728 to pass through the TP into the LA. A flexible section 712, which may for example be constructed in accord with the teaching of the '117 application, is then pushed along the rigid sheath 722 (utilizing the longitudinal rigidity of the flexible section 712) until a distal end of the flexible section 712 extends through the opening in the interatrial septum and into the LA, as shown in
The ablation catheter 724 is then advanced distally through the rigid sheath 722 until the cryogenic tip 726 extends distally beyond the distal end of the rigid sheath 722 and the distal end of the flexible section 712. Several known techniques may be used for maneuvering catheter 724 to a desired position within the opening of the one of the PV's from which the contraction origination signals are improperly originating. In certain embodiments, the catheter 724 is deflectable via a deflection mechanism associated with the catheter handle, which may ease the positioning of the catheter. Furthermore, by advancing the rigid sheath 722 further into the LA, a pre-formed bend in the tip of the rigid sheath 722 may be employed to assist in aiming the cryogenic tip 726 toward the desired PV opening. After the cryogenic tip 726 has been properly positioned well within the PV, the flexible section 712 is advanced distally along the ablation catheter 724 until the distal end of the flexible section 712 is near the orifice at which the PV opens into the LA. To aid in ensuring proper positioning of the cryogenic tip 726 and the flexible section 712 in the orifice of the PV, the flexible section 712 and the rigid sheath 722 may include radiopaque markers at the respective distal ends thereof, or at other desired locations.
Once the flexible section 712 has been positioned near the opening of the PV, the user may inject contrast media into the PV via the flexible section 712. The contrast media may exit the flexible section 712 via openings 736 of the flexible section 712. This may be done to aid in locating, under fluoroscopic imaging, the orifice of the PV. The user may then inflate the balloon 718 to occlude the PV. In one embodiment, the inflation fluid may be a diluted contrast media solution such that the balloon 718 may more easily be seen under imaging. The flexible section 712 is then advanced until the balloon 718 is seated on the orifice of the PV, thereby occluding the flow of blood from the PV into the LA as shown in
In the preceding specification, the present invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broadest spirit and scope of the present invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative rather than restrictive sense. For example, while the invention has been described for use with PV ablation, the device may be used in other parts of the vascular system.
While the particular cryoablation systems and methods as herein shown and disclosed in detail are fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that they are merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.
