BACKGROUND OF THE INVENTION
This invention is directed to an elongated catheter adapted to facilitate delivery of a therapeutic or diagnostic device into a body cavity such as the left ventricle of a patient's heart, and particularly for the treatment of myocardial tissue experiencing ischemic conditions by revascularization of such tissue.
Myocardial revascularization typically involves formation of one or more channels in a patient's heart wall defining the heart chamber to treat a patient's ischemic myocardial tissue therein. The first trials of the revascularization process was made by Mirhoseini et al. See for example the discussions in Lasers in General Surgery (Williams & Wilkins; 1989), pp 216-223. Another early disclosure of this procedure is found in U.S. Pat. No. 4,658,817 (Hardy). Both of these references describe revascularization procedures which require the chest wall to be opened and which include formation of the revascularization channels through the epicardium, myocardium and endocardium, i.e. the entire heart wall.
Copending application Ser. No. 08/368,409, filed on Dec. 30, 1994, which is incorporated herein in its entirety, describes an intravascular system for percutaneous transmyocardial revascularization (PTMR) which is introduced into a peripheral artery and advanced through the patient's arterial system into the left ventricle of the patient's heart. The revascularization channels are formed through the endocardium and into the myocardium from within the left ventricle. This procedure eliminates the need of the prior intraoperative procedures which require opening the chest cavity and penetrating the entire heart wall to form a channel through the endocardium into the myocardium.
While the percutaneous method and system for introducing the revascularization device developed by Aita et al. was a substantial advance, one of the difficulties in forming revascularization channels from within a patient's left ventricle by means of a percutaneously introduced revascularization system was to accurately direct the distal tip of the channel forming device to a desired region of the patient's endocardium and to maintain the placement of the distal end of the channel forming device against a desired region of the ventricular wall at a proper angle while the heart was beating. Copending application, Ser. No 08/646,856 filed May 8, 1996, which is incorporated herein in its entirety, describes an intravascular system using one or more delivery catheters which may have a preshaped or shapeable distal extremities to facilitate directing a therapeutic or diagnostic device slidably disposed within the catheter lumen toward the region of the endocardium where the procedure is to be performed.
What has been needed is a guiding or delivery catheter with the maneuverability desired for advancing through the patient's vasculature yet having sufficient strength and rigidity to support a channel forming device within the patient's heart chamber. The present invention satisfies these and other needs.
SUMMARY OF THE INVENTION
The present invention is directed to intraluminal catheters which aid in positioning a therapeutic or diagnostic device within a patient's body region such as a heart chamber. The intraluminal catheter of the invention generally has an elongated tubular shaft with proximal, intermediate, and distal shaft sections. The intermediate shaft section has greater flexibility than the proximal or distal shaft sections. The distal shaft section may have equal or greater flexibility than the proximal shaft section.
The relative flexibility or the inverse stiffness of the various shaft sections may be achieved with conventional techniques used in catheter design, including selection of materials and wall thickness, and the use of reinforcing means such as strands, coils and the like. For example, a thin walled intermediate shaft section would have high flexibility relative to thicker walled proximal or distal shaft sections made from the same or similar materials. Alternatively, the material used in the intermediate shaft section may be inherently more flexible than a different material used in the proximal or distal shaft sections. Likewise, the catheter shaft sections may be formed of the same material with the distal and proximal sections provided with reinforcing stands or coils.
In accordance with one aspect of the invention, the intraluminal catheter is a delivery catheter for directing an elongated intraluminal device to a desired region within the patient's body such as the patient's heart chamber. The catheter shaft has proximal and distal ends, and a lumen extending to and in fluid communication with a port in the distal end of the catheter. The port and inner lumen are configured to slidably receive an elongated therapeutic or diagnostic device. A typical delivery catheter device of the invention is particularly suitable for delivery of an elongated device for forming a channel into the wall defining the heart chamber or a device for performing other ablation treatments and diagnosis.
For the percutaneous delivery of therapeutic or diagnostic devices into a patient's left ventricle the delivery catheter is of a length sufficient to have a proximal extremity extending out of the patient and a distal extremity extending into the patient's left ventricle. The overall length of the catheter is preferably about 100 cm to about 120 cm, and typically about 105 cm. The length of the intermediate section is about 5 to about 50 cm, and preferably about 20 cm to about 30 cm, so that it extends through at least a substantial portion of a human patient's aortic arch. The length of the distal section is about 2 to about 10 cm, and preferably about 4 cm to about 8 cm to ensure that the distal end of the catheter shaft extends into the left ventricle of the patient's heart. Therefore, the intermediate shaft section is a length at least about 2 to about 8, and preferably about 4 times the length of the distal shaft section.
In a presently preferred embodiment, the distal shaft section is relatively short when compared to the intermediate shaft section. Additionally, the proximal shaft section is relatively long compared to the intermediate and distal shaft sections. When the distal end of the catheter has been advanced through a patient's aortic passageway and into the left ventricle or slightly downstream thereof, the more flexible intermediate shaft section occupies aortic arch, or at least a significant portion thereof, slightly downstream of the aortic valve. The relatively stiff proximal shaft section extends from the proximal extremity of the delivery catheter outside the patient to a point within the descending aorta downstream of the aortic arch. The distal shaft section extends from the flexible intermediate shaft section to the distal end of the delivery catheter within the left ventricle.
The catheter of the invention is particularly suitable for delivery of therapeutic or diagnostic devices such as laser based optical fiber systems for forming channels within the wall of the patient's heart, i.e. PTMR. The optical fiber system which is adapted to emit laser energy from its distal end, is slidably disposed within the lumen of the delivery catheter and is of a length sufficient to extend out the port in the distal end of the catheter to engage tissue of the endocardium while forming the channel or performing other types of procedures. The distal end of the catheter is preferably shaped so that when positioned within the patient's heart chamber, it provides the desired orientation for the delivered therapeutic or diagnostic device toward the region of the endocardium where the procedure is to be performed.
The delivery catheter of the invention may be advanced through a previously introduced guiding catheter which has a lumen in fluid communication with a port in the distal end of the catheter. In accordance with one aspect of the invention, the guiding catheter of the invention itself has a flexible intermediate shaft section between less flexible proximal and distal shaft sections, in the same or similar manner as the delivery catheter. The discussion above relating to the relative flexibility and length of the proximal, intermediate, and distal sections on the delivery catheter applies equally well for the corresponding sections on the guiding catheter of the invention. Whether the guiding catheter is advanced until its distal end is disposed within the left ventricle or at least within the ascending aortic passageway downstream of the left ventricle, the flexible shaft section is sized and positioned on the catheter to occupy a significant portion of the aortic arch. A nontraumatic distal tip may be provided on the guiding catheter in a conventional manner.
In one presently preferred method of practicing the invention, the delivery catheter is percutaneously introduced into a patient's peripheral artery, such as the femoral artery, and advanced through the patient's arterial system until the distal end is disposed within the patient's left ventricle or slightly downstream of the aortic valve in the ascending aorta. The delivery catheter may be advanced over a guidewire or within a guiding catheter previously introduced which has a distal extremity positioned within the left ventricle or within the ascending aorta slightly downstream of the aortic valve. When myocardial revascularization is to be performed, an intravascular device having a means to form channels in the patient's heart wall is advanced through the lumen of a properly positioned delivery catheter until the operative end of the device is positioned at a desired location within the patients heart. The position of the delivery catheter and the intravascular device may be adjusted to precisely access a desired region of the endocardium.
Providing a flexible intermediate shaft section on a catheter between the stiffer proximal and distal shaft sections of the catheter facilitates passage of the catheter through the aortic passageway. Catheter designs without this flexible section will have difficulty advancing through the aortic arch, and will likely contact the aortic wall. The result of the contact with the aortic wall can be trauma to the wall and frictional drag on the catheter hindering its maneuverability. Catheter designs with flexibility in the distal region that is uniform or ever increasing towards the distal tip fail to provide the torque control and kink resistance inherent in the design of the invention. Moreover, when contact with the heart wall does result, catheters having a flexible intermediate shaft section will produce lower point loads against the wall than would be produced by conventional catheters.
The flexible intermediate shaft section reduces the combined system stiffness of a delivery catheter within a guiding catheter. This, along with a reduction in the pushing force produced from contact of the catheter distal end with the heart wall, lowers the force against the heart wall and the drag on rotation of the catheter. Unlike the catheter of the invention, conventional catheters in contact with a heart wall produce a significant pushing force against the heart wall which restricts the freedom of rotation of the catheter. These and other advantages of the invention will becom more apparent from the following detailed description of the invention and the accompanying exemplary drawings.
As shown in FIG. 1, the delivery catheter 10 of the invention generally includes an elongated shaft 11, a proximal shaft section 13, an intermediate shaft section 14, and a distal shaft section 15. The distal shaft section 15 has a distal end 16 with a port 17 in fluid communication with a lumen 18 extending through the catheter shaft 11. A therapeutic or diagnostic device 19, such as an ultrasonic, laser, or electrode based device for tissue ablation or sensing, is slidably disposed within the lumen 18 of the delivery catheter 10. In FIG. 1 the therapeutic device 19 illustrated is a revascularization device, such as described in copending application Ser. No. 08/584,957 (M. A. Javier, Jr. et al.) filed on Jan. 11, 1996, which is incorporated herein by reference.
The delivery catheter 10 and guiding catheter 20 intermediate shaft sections 14 and 24 are constructed to be relatively flexible compared to the proximal and distal shaft sections, to facilitate advancement of the catheters through the ascending aorta 41. The proximal and distal shaft sections have stiffnesses of about 2, preferably about 3 times that of the flexible intermediate shaft section. A method of measuring the desired stiffness which has been found suitable is a modification of ASTM test D747. This modification measures the load required to deflect a cantilevered specimen 12.7 mm from the fixed end a distance of 1 mm. For the intermediate shaft section of the delivery catheter, a suitable load is about 5 to about 30 gms, preferably about 10 to 20 gms. For the proximal and distal stiff shaft sections, the loads should range about 20 to 70 gm, preferably about 30 to 50 gms. Guiding catheters are generally stiffer than the delivery catheters and the load ranges about 60 to about 200 gms, preferably about 100 to 150 gms for the proximal and distal shaft sections, and about 30 to 100 gms preferably about 50 to 80 gms for the flexible intermediate shaft sections. In a presently preferred embodiment, the load values of the proximal and distal shaft sections of a catheter are substantially similar. However, it may be desirable to have a proximal shaft section with a higher load value, i;e., greater stiffness, than the distal shaft section. The various catheter shaft sections may be formed of conventional materials providing the desired flexibility and strength characteristics. For example, the delivery catheter 10 intermediate shaft section 14 may be a relatively flexible material such as PEBAX 55D, and the proximal and distal shaft section may be a high strength, stiff material such as PEBAX 72D or nylon, and is preferably PEBAX 72D. The wall thickness of the intermediate shaft section may be about 0.050 mm to about 0.20 mm less than the wall thickness of the proximal and distal shaft sections to provide an intermediate shaft section with the desired flexibility relative to the other shaft sections.