System for treatment of heart tissue using viability map

Surgery – Instruments – Light application

Reexamination Certificate

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C606S010000

Reexamination Certificate

active

06447504

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to methods and devices for cardiac surgery, and specifically to methods and apparatus for revascularization, particularly for transmyocardial laser revascularization (TMR).
BACKGROUND OF THE INVENTION
TMR is a technique, known in the art, for creating channels in ischemic heart tissue, typically in the left ventricular wall of the heart, to improve the blood supply to ischemic myocardium. The technique is described, for example, by Mirhosein, et al., in an article entitled “Transmyocardial Laser Revascularization: A Review,” in the Journal of Clinical Laser Medicine & Surgery, vol. 11 (1993), pages 15-19, and by Bonn, in an article entitled “High-power lasers help the ischaemic heart,” in The Lancet, vol. 348 (1996), page 118, which are incorporated herein by reference.
In TMR, as is known in the art, a computer-controlled laser is used to drill holes about 1 mm in diameter in the myocardium, communicating with the left ventricle, at a typical density of about one hole per square centimeter. Typically, the laser beam is delivered to the epicardium through an incision in the chest and the pericardium that exposes the beating heart. The laser, typically a CO
2
laser or, alternatively, an excimer or Ho:YAG laser, fires pulses of about 1000W, which photovaporize the myocardium and create channels through the endocardium into the ventricle. Blood at the outer, epicardial openings of the channels typically clots after a few minutes, but the inner portions of the channels, communicating with the ventricle, remain patent. It is hypothesized that during systole, blood flows through these channels into naturally-existing myocardial sinusoids, supplementing the impaired arterial blood supply.
Particularly when a CO
2
laser is used, the laser is generally synchronized to the patient's ECG, so as to fire its pulse during systole, in the refractory period of the heart cycle. Firing the laser pulse at other points in the heart cycle can cause undesirable arrhythmias. The heart rate, myocardial thickness and other factors are used to determine the optimum energy level for each laser pulse.
U.S. Pat. Nos. 5,380,316 and 5,554,152, to Aita, et al., which are incorporated herein by reference, describe methods for intra-operative myocardial revascularization using an elongated, flexible lasing apparatus, which is inserted into the chest cavity of the patient. The distal end of the apparatus is directed to an area of the exterior wall of the heart adjacent to a ventricle and irradiates the wall with laser energy to form a channel through the myocardium.
U.S. Pat. No. 5,389,096, to Aita, et al., which is also incorporated herein by reference, describes methods and apparatus for percutaneous myocardial revascularization (PMR). A deflectable, elongated lasing apparatus is guided to an area within the patient's heart, and the distal end of the apparatus is directed to an area of interest in the inner wall of the heart. The wall is irradiated with laser energy to form channels therein, preferably without perforating the epicardium.
Since in PMR the channels are drilled from the inside of the heart outwards, there is no need for the channels to penetrate all the way through the heart wall, unlike more common TMR methods, in which the channels are drilled from the outside in. In other respects, however, the effects of PMR on the heart are substantially similar to those of TMR. Therefore, in the context of the present patent application, the term TMR will be used to refer to both extracardial and intracardial methods of laser revascularization of the myocardium.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide improved methods and apparatus for TMR.
It is a further object of some aspects of the present invention to provide improved control over the TMR laser drilling procedure, and specifically to control the depth and direction of drilling.
In accordance with some aspects of the present invention, holes are drilled into the myocardium at controlled, substantially predetermined angles. Preferably, the holes are drilled at oblique angles, so as to produce longer channels through the tissue. These longer channels communicate with a greater volume of the myocardium than do channels drilled at approximately right angles to the heart wall, as are known in the art. The oblique channels thereby enhance the perfusion of ventricular blood in the tissue, and may communicate with greater numbers of myocardial sinusoids than do right-angle channels.
It is still another object of some aspects of the present invention to provide methods for mapping and sensing physiological signals in the heart tissue, to be used in conjunction with TMR to adapt and optimize the drilling procedure for the local conditions prevalent in the drilling area in the heart under treatment.
In preferred embodiments of the present invention, a catheter for use in TMR treatment comprises an optical or infrared waveguide and at least one sensor, adjacent the catheter's distal end. The catheter has a distal end, which is surgically inserted into the body and brought into engagement with a surface of the heart muscle, and a proximal end, which is coupled to a console outside the body. The waveguide, preferably an infrared optical fiber, as is known in the art, receives a beam from a high-power laser preferably a pulsed CO
2
laser, Ho:YAG or excimer laser, as are known in the art, at the proximal end of the catheter, and directs it at the heart surface. The console receives and analyzes signals from the sensor, in order to guide and control the treatment.
In some preferred embodiments of the present invention, the catheter is inserted into a chamber of the heart, preferably into the left ventricle, by passing the catheter percutaneously through the arterial system. Alternatively, the catheter may be passed through the venous system into the right atrium and ventricle. In these preferred embodiments, the catheter engages the endocardium, and the laser is fired to drill holes into the myocardium from the inside. Preferably, these holes are drilled only to a limited depth, without penetrating the epicardium. Further preferably, the holes are drilled to a depth that is generally sufficient to communicate with the myocardial sinusoids, preferably no more than 8 mm deep, measured in a direction perpendicular to the surface of the heart tissue. More preferably the holes are drilled to a depth of no more than 6 mm, and most preferably, to a depth of about 3 mm.
In other preferred embodiments of the present invention, the catheter is inserted through a surgical incision in the chest wall and then through the pericardium. The catheter engages the epicardium of the left ventricle, and the laser is fired to drill holes through the myocardium and into the left ventricle, guided by the signals received from the sensor at the catheter's distal end.
Preferably, the holes drilled in the heart tissue are approximately one millimeter in diameter. In some preferred embodiments of the present invention, the holes have elliptical, rather than circular cross-section. The elliptical holes have a greater surface area than circular holes of the same cross-sectional area, and therefore may be more effective in enhancing the perfusion of blood into the myocardium. Preferably, the waveguide is flared at the distal end of the catheter to provide an output laser beam profile having a shape and diameter substantially similar to the desired shape and diameter of the holes to be drilled.
In some preferred embodiments of the present invention, the laser is focused onto the heart tissue at a sufficiently high power density to generate shock waves in the tissue. For CO
2
laser irradiation, the power density is preferably at least 1 MW/cm
2
. The shock waves cooperate with the photovaporization effect of the laser beam incident on the tissue to drill holes in the myocardium which, it is believed, are more effective in improving perfusion of the myocardium than holes drilled

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