Mechanism of TMR; the debate continues.

Clinical experience with transmyocardial laser revascularization has increased significantly over the last few years. Since several transmyocardial laser revascularization studies reported an apparent effect on the relief of angina and the FDA approved reimbursement of transmyocardial laser revascularization procedures in the USA, thousands of patients have been treated worldwide with different laser systems using a surgical (transmyocardial laser revascularization) or a percutaneous approach. However, the mechanisms underlying the apparent benefit are not yet fully elucidated and many studies report different potential mechanisms of action. In addition, the paper of Reuthebuch et al. published in this issue does not provide data which helps us to reach a consensus about one proposed mechanism of action. Contrary to the current belief of rapid loss of patency, they demonstrate long-term patency of the laser channels created by a CO2 laser by a contrast echocardiography technique. Initially, Mirhoseini, a pioneer in transmyocardial laser revascularization procedures in the late 1970s, proposed the idea of direct myocardial perfusion from the left ventricle cavity with a laser, thus mimicking the reptilian physiology. However, evidence of postprocedural patent laser channels has been conflicting. Apart from one post mortem case report showing some patent small tracts within a laser channel remnant 94 days post CO2 laser transmyocardial laser revascularization procedure others failed to show such patent channels. Postmortem analysis of a deceased transmyocardial laser revascularization patient 4Y weeks after the transmyocardial laser revascularization procedure using a CO2 laser, showed no patent laser channels but channel remnants filled with fibrous scar. These findings were substantiated by a report from Gassler et al., who investigated the hearts of three transmyocardial laser revascularization patients who died 3, 16 and 150 days after the CO2 laser procedure. In all the three patients no patent channels were found, nor were the channels lined with endothelium. At different time points the laser channels showed an inflammatory healing response with the formation of