Transmyocardial laser revascularization: effect of laser parameters on tissue ablation and cardiac perfusion

Dr. Mahmood Mirhoseini from Milwaukee, WI, transformed transmyocardial revascularization (TMR) into transmyocardial laser revascularization (TMLR) more than 2 decades ago. The controversial nature of this laser procedure and the prospect of its successful application to refractory cases of chronic debilitating angina have created spirited interest in TMLR. As a natural component of this interest, various laser modalities have been proposed and employed during the performance of the TMLR procedure both in the experimental and the clinical setting. However, it is the nature of laser-tissue interactions that is primarily responsible for the long-term fate of the channels, the angiogenesis that occurs in the vicinity of these laser channels, and the resulting increase (if any) in myocardial perfusion. These interactions with tissue are, in turn, determined by laser variables such as photonic absorption and scattering by the target tissue, pulse energy and duration, and the peak power generated. The CO2 laser has the advantages of producing high-energy pulses that create a transmural channel with a single pulse, low-peak power that minimizes structural tissue trauma, and high photonic absorption to minimize thermal damage. The holmium:YAG and excimer lasers, in turn, have the advantage of being coupled to a fiber optic catheter for transluminal endocardial delivery. Importantly, long-term clinical and perfusional data showing a cause and effect relationship between the use of TMLR and these end-points are available for the CO2 laser only. Prospective randomized trials are, therefore, warranted to delineate the use of each laser modality in relation to that of the CO2 laser in the TMLR setting.