CO_2, Ho : YAG, and Er : YAG Lasers for Transmyocardial Laser Revascularization

摘要

Transmyocardial laser revascularization (TMLR) has been shown to improve symptoms in patients with severe diffuse coronary artery disease, who are not candidates for coronary bypass or percutaneous transluminal coronary angioplasty procedures. TMLR is based on the hypothesis of direct perfusion of the ischemic myocardium via the laser created channels. However, the mechanism of action is still unclear and controversially discussed. The basic interaction mechanisms of IR-laser radiation with myocardium and the short- and long-term tissue effects were evaluated after Er : YAG, Ho : YAG and CO_2 laser impact in order to determine the optimal type and characteristics of laser for TMLR. Regardless of the laser source, all channels were occluded within 6 weeks. Minimal acute thermal damage by Er : YAG laser resulted in small scar formation. Tissue tearing caused by pulsed Ho : YAG irradiation was initially stronger than after continuous wave CO_2 irradiation leading to scars extending along separated fiber planes. The scar appearance after 6 weeks is however, indistinguishable from CO_2 laser, both characterized by newly formed vessels and a large number of capillaries in the scar. The fast channel occlusion suggests that rather than revascularization, subsidiary physiological tissue effects elicited by the thermal, oxidative or mechanical action of the laser impact contribute to the beneficial clinical effects of TMLR. This study may provide a theoretical basis for the clinical application of TMLR in the treatment of ischemic heart disease.