Transmyocardial Laser Revascularization
Mahmood Mirhoseini, M.D., Mary M. Cayton, BSN
St. Luke's Medical Center, Milwaukee, WI
The concept, Transmyocardial Laser Revascularization, was based on the work of early investigators who were seeking to emulate reptilian circulation in the mammalian heart. A variety of techniques which included needle acupuncture, punch biopsy boring of left ventricular conduits, and insertion of T-Tubes into the left ventricle were attempted. Initial results, in the first one to two months, were promising. The mechanical injury, initiated the sequence of cell infiltration, fibrosis, scarring, and closure of these channels after two months. These early studies were important. The findings indicated that perfusion of the myocardium, from the ventricular cavity through the created channels, was possible if a method could be found to avoid mechanical trauma and early closure.
A study of what was then a new source of energy, the laser, which was developed in the mid 1960's by Maimon, and an interest in the work of the early investigators led us to formulate the hypothesis that channels created in the left ventricle by the laser would perfuse and nourish the myocardium, remain patent, and protect the muscle from ischemic changes. The hypothesis was developed based on the physiology of myocardial perfusion patterns and the biophysics of laser tissue interactions.
In 1969, Thomas Polyani, Ph.D., of American Optical Company, Framingham, MA provided us with an opportunity to test this hypothesis, using a high power prototype CO2 laser, on the beating heart. The initial tests provided enough information to proceed with further studies. The high power prototype laser was installed in our laboratory and a series of investigational studies began. Following coronary ligation infarct size was smaller in hearts that were revascularized by laser, mortality was reduced, and the channels remained patent. Various techniques to demonstrate quantitative myocardial perfusion were tried. Our conclusion was that the results indicated that, indeed, the hypothesis appeared valid and further study was needed.
The results of this initial work were presented at the Wisconsin Surgical meeting in 1971, Second Henry Ford Congress for Cardiovascular Surgery in 1977, and World Microsurgery Congress II in 1978. Initial publications were in the proceedings of the Wisconsin Surgical Society 1971, the proceedings of the Henry Ford Symposium 1977, and the Journal of Microsurgery in 1981.
The prototype high power CO2 laser was a research instrument. The development of the first articulated arm for delivery of laser energy was by Herbert Bredermeir Ph.D. and Robert Wallace of American Optical Company. The development of other fundamental concepts that were later adapted for general use on clinical laser systems, were a direct result the early work by several pioneers with this, and another early CO2 laser of lower energy, the "telephone booth". Although these were early models many sophisticated technical and electronic systems were incorporated into the working mechanisms and delivery systems.
Although all the early work was done with a high power laser on the beating heart, this laser was not readily adaptable to the operating room environment. In the late 1970's and early 1980's experiments were conducted to modify the technique for use with the low power laser, which was then readily available. The procedure was done in combination with cardiopulmonary bypass on the cooled heart, arrested with cardioplegia solution. In 1982 a proposal was submitted to the Institutional Review Board of St. Luke's Medical Center to begin clinical investigation of this technique on patients who were undergoing conventional coronary artery bypass but who had areas of ischemia not amenable to graft insertion. During this time one patient, who could not be weaned from cardiopulmonary bypass following coronary artery bypass grafting, was revascularized using the low power laser and subsequently successfully weaned from bypass. This patient had an uneventful postoperative course. This case report was presented at the Fourth International Congress of Laser Medicine and Surgery 1983, and published in Lasers in Surgery and Medicine. It was also at this time that John Fisher, Sc.D became interested in this procedure, and arranged for us to perform two procedures in Marseilles, France with Dr. Jean Pierre Bex.
Initial approval by St. Luke's Institutional Review Board, in late 1983, was for a series of 12 patients to undergo Transmyocardial Laser Revascularization in conjunction with coronary artery bypass. The results of this early clinical study were promising, although clouded by the presence of the coronary artery grafts. The study is significant in demonstrating that the laser could be used safely on the heart and that the channels remained patent. Permission was obtained to continue the study, and the combined procedure remains an option in selected patients. The results of this early clinical investigation were presented at the annual meeting of the American Society for Lasers in Medicine and Surgery in 1985 and the annual meeting of the Society of Thoracic Surgeons in 1987. Publications were in The Journal of Clinical Medicine and Surgery and the Annals of Thoracic Surgery.
Our efforts, underway since the early investigational studies, to develop a high power laser for clinical use on the beating heart continued. Although the main focus of interest was the CO, laser because of the biophysics of tissue interaction, exhaustive studies of other wavelengths were also conducted.
In 1987 Dr. M. Okada, Kobe University, used the low power laser to successfully revascularize the ischemic myocardium, on the beating heart, in a patient in whom he was unable to insert bypass grafts because of severe pericarditis.
Development of the clinical high power CO2 laser system, the Heart Laser, for transmyocardial laser revascularization on the beating heart, under Robert Rudko, Ph.D. of Laser Engineering, now PLC Medical Systems, led to the first FDA approved clinical trials in the United States. The first procedure with the system, by Dr. John Crewe at Seton Medical Center, San Francisco, was followed by opening a clinical site at our institution.The following year other clinical sites were added. At present several clinical trials are underway in the United States, Europe, the Middle East, Asia, and South America.
Accumulating clinical data, as well as results from experimental studies being conducted at this and at many other institutions throughout the world, may answer some of the fundamental questions regarding physiological mechanisms and technical considerations. Verification of the effect of TMLR was originally based on nuclear studies. The assessment by PET scanning, as performed by the group at Texas Heart Institute, Dr. Cooley, Dr. Frazier, and K. Kadipasaoglu, Ph.D., has been a valuable contribution.
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