Surgery – Instruments – Light application
Reexamination Certificate
2000-10-12
2002-08-20
Gibson, Roy D. (Department: 3739)
Surgery
Instruments
Light application
C606S015000, C607S122000, C607S101000, C604S095010
Reexamination Certificate
active
06436095
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to methods and devices for cardiac surgery, and specifically to methods and apparatus for myocardial revascularization.
BACKGROUND OF THE INVENTION
Myocardial revascularization is a technique, known in the art, for creating channels in ischemic heart tissue to improve the blood supply to ischemic myocardium. It may be performed by various techniques, the best-known of which is laser myocardial revascularization, which employs laser radiation for generating such channels.
In transmyocardial revascularization (TMR), as is known in the art, a computer-controlled laser is used to drill penetrating holes about 1 mm in diameter in the myocardium by delivering laser energy to the epicardium through an incision in the chest and the pericardium. 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.
According to another hypothesis, the local injury caused to the myocardium by various forms of energy (e.g., laser radiation, as described above, or alternatively, RF radiation, or ultrasonic or mechanical energy) stimulates local angiogenesis, eventually supplementing the impaired arterial blood supply. Although there are no conclusive answers at present regarding the underlying mechanism, there is clinical evidence of the treatment's therapeutic efficacy.
U.S. Pat. No. 5,389,096, to Aita, et al., which is 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. Alternatively, PMR may be carried out by applying other energy forms, as described above, from inside the art.
In TMR, as is known in the art, the channels are created through the myocardium from the outside in, and the transient blood stream ensuing upon channel completion constitutes an intrinsic indication of successful drilling. In PMR, however, the channel is generated from inside the heart chamber and, preferably, does not penetrate the myocardium. Consequently there is no direct indication of successful generation of the channel.
A PMR procedure, whether employing laser energy or any other suitable energy form, may fail due to a multiplicity of reasons. For example, referring specifically to laser PMR, the catheter inserted into the heart may be incorrectly oriented, so that the energy does not impact and penetrate the endocardium, or does not penetrate to a significant depth. Alternatively, the distal end of the catheter may be obstructed, for example, by a thrombus and/or ablated tissue residues. Because systems for PMR known in the art do not give any indication of whether the energy pulse has successfully generated a channel in the myocardium, it is difficult or impossible for an interventional cardiologist to detect and correct such a failure during the procedure.
SUMMARY OF THE INVENTION
It is an object of some aspects of the present invention to provide a reliable indication as to whether an energy pulse locally imparted to the heart has successfully produced a channel in the myocardium.
It is a further object of some aspects of the present invention to provide methods and apparatus for monitored PMR.
In the context of the present patent application and in the claims, the term “PMR” is taken to refer to any and all techniques of percutaneous myocardial revascularization treatment, including laser, RF, ultrasound and mechanical methods, but not limited thereto. Accordingly, while preferred embodiments of the present invention are described herein largely in terms of creating channels in the myocardium using laser irradiation, those skilled in the art will understand that the principles of the present invention are similarly applicable to other PMR techniques.
Some aspects of the present invention are based on the finding by the inventors that when an energy pulse is incident on the myocardium in such a manner as to create a channel therein, it causes detectable variations in the heart's electrical activity, both local and global. In particular, the applicants have observed such variations when a laser beam creates a channel in the myocardium.
The local variation is expressed in the form of an elevated ST segment in the locally-measured electrogram. The elevated ST is characteristic of injuries to the heart, and is observed to last for at least several minutes after generating the channel. It is a distinctly local effect, and is not observed outside a diameter of several millimeters (typically 3 mm) from the point at which the channel is generated.
The global variation is observed in the form of disturbance of the heart's sinus rhythm, typically in one or more ventricular premature beats (VPB's) immediately following the laser pulse. The VPB's are observed both in electrogram signals recorded within the heart chamber and in ECG signals recorded on the body surface.
It is still another object of some aspects of the present invention to provide indication that the channels have been generated in accordance with predetermined dimensions, location and orientation. These aspects of the invention are based primarily on the ability of ultrasonic waves to resolve zones of differing tissue characteristics, in particular density, thus imaging the channels' dimensions and direction.
Other aspects of the present invention use real-time sensing technologies, particularly based on optical sensing, for detecting local changes in blood perfusion. By comparing pre- and post-PMR optical signals, enhanced blood perfusion of ischemic zones, due to successful channel generation, may be observed.
Some preferred embodiments of the present invention are based on a PMR catheter as described in PCT patent application no. PCT/IL97/00011, filed Jan. 14, 1997, which is assigned to the assignee of the present patent application, and whose disclosure is incorporated herein by reference. The catheter comprises a waveguide, for conveying energy to the endocardium, preferably laser energy, and has at least one sensor at its distal tip. The sensor may comprise one or more electrophysiological sensing electrodes, position sensors, ultrasound transducers, or other sensors known in the art.
In some of these preferred embodiments, the sensor comprises an electrode, which receives electrical signals from the heart indicative of the efficacy of local PMR treatment, i.e., whether an energy pulse or series of pulses has actually succeeded in generating a channel of substantial depth in the myocardium. The catheter is coupled to signal processing circuitry, which processes the signals received by the electrode and provides an indication to a user of the catheter, typically an interventional cardiologist, as to whether the channel has been generated. The indication is typically based on elevation of the ST segment and/or VPB's in the local electrogram during at least several minutes after the channel has been generated. Failure to sense such a change after one or several energy pulses is taken to be an indication of an error or malfunction, requiring the cardiologist's intervention. Preferably, the catheter is held in place at a candidate site for a period both before and after channel generation, long enough to gather pre- and post-PMR electrograms, which are compared to ascertain the efficacy of the local treatment.
Preferably, the elevated ST effect, which is of a highly localized nature and significantly long duration, also provides an indication to the user during subsequent PRM channel generation
Ben-Haim Shlomo
Yaron Uri
Zilberstein Joel
Biosense Inc.
Capezzuto Louis J.
Gibson Roy D.
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