Laser-tissue interaction during transmyocardial laser revascularization

The clinical procedure known as transmyocardial revascularization has recently seen its renaissance. Despite the promising preliminary clinical results, the associated mechanisms are subject to much discussion. This study is an attempt to unravel the basics of the interaction between 800 W carbon-dioxide laser radiation and biological tissue. Time-resolved flash photography was used to visualize the laser-induced channel formation in water and tissue phantoms. In addition laser-induced pressures were measured. Channel depth was shown to increase logarithmically with time (i.e. with pulse duration) in water, tissue phantoms and porcine myocardium. Pressure measurements show numerous small transients during the laser pulse which corresponded to the local and partial collapse of the formed channel already during the pulse. It was shown that in tissue, 20 mm of myocardium is perforated in 25 ms. Increasing the pulse duration only has a small effect on the maximum transversible thickness while histology shows that thermal damage around the crater increased with increasing pulse duration.