CO2, Ho : YAG, and Er : YAG lasers for transmyocardial laser revascularization

Transmyocardial laser revascularization (TMLR) has been shown to improve sy mptoms in patients with severe diffuse coronary artery disease, who are not candidates for coronary bypass surgery or percutaneous transluminal corona ry angioplasty procedures. TMLR is based on the hypothesis of direct perfus ion of the ischemic myocardium via the laser created channels. However, the mechanism of action is still unclear and controversially discussed. The ba sic interaction mechanisms of IR-laser radiation with myocardium and the sh ort- and long-term tissue effects were evaluated after Er :YAG, Ho :YAG and CO2 laser impact in order to determine the optimal type and characteristic s of laser for TMLR. Regardless of the laser source, ail channels were occl uded within 6 weeks. Minimal acute thermal damage by Er :YAG laser resulted in small scar formation. Tissue Gearing caused by pulsed Ho :YAG irradiati on was initially stronger than after continuous wave CO2 irradiation leadin g to scars extending along separated fiber planes. The scar appearance afte r 6 weeks is, however, indistinguishable from CO2 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, subsid iary physiological tissue effects elicited by the thermal, oxidative or mec hanical action of the laser impact contribute to the beneficial clinical ef fects of TMLR, This study may provide a theoretical basis for the clinical application of TMLR in the treatment of ischemic heart disease.