LASER-TISSUE INTERACTION DURING TRANSMYOCARDIAL LASER REVASCULARIZATION

Background. The clinical procedure known as transmyocardial revascular ization has recently seen its renaissance. Despite the promising preli minary clinical results, the associated mechanisms are subject to much discussion. This study is an attempt to unravel the basics of the int eraction between 800-W CO2 laser radiation and biological tissue. Meth ods. Time-resolved flash photography was used to visualize the laser-i nduced channel formation in water and in vitro porcine myocardium. In addition, laser-induced pressures were measured. Light microscopy and birefringence microscopy were used to assess the histologic characteri stics of laser-induced thermal damage. Results. The channel depth incr eased logarithmically with time (ie, with pulse duration) in water and porcine myocardium. Pressure measurements showed the occurrence of nu merous small transients during the laser pulse, which corresponded wit h channel formation, as well as local and partial channel collapse dur ing the laser pulse. Twenty millimeters of myocardium was perforated i n 25 ms. Increasing the pulse duration had a small effect on the maxim um transversable thickness, but histologic analysis showed that therma l damage around the crater increased with increasing pulse duration. C onclusions. Several basic aspects of the interaction of high-power CO2 laser radiation with myocardial tissue and tissue phantoms were studi ed in vitro. Although the goal of this study was not to unravel the me chanisms responsible for the beneficial effects of transmyocardial rev ascularization, it provided important information on the process of ch annel formation and collapse and tissue damage. (C) 1997 by The Societ y of Thoracic Surgeons.