Exploring the scientific basis of surgery: Transmyocardial revascularization

Transmyocardial revascularization (TMR) is a new surgical procedure aimed a t increasing blood flow to the ischemic myocardium. It has been used for tr eatment of patients with end-stage coronary artery disease who are not cand idates for conventional measures such as medication, percutaneous translumi nal coronary angioplasty, and coronary artery bypass grafting. TMR involves creating transmural channels in the myocardium using lasers, in areas show n to be ischemic during preoperative testing. This procedure has shown prom ising results in clinical trials, but the mechanism of its efficacy remains largely unknown. TMR was originally developed as a means of supplying bloo d to the ventricular myocardium, directly through channels made in the wall of the ventricle. This was in an attempt to recreate the situation that ex ists in the reptilian heart, in which the myocardium is perfused directly f rom the ventricular chamber through a rich network of sinusoids that bathe the myocardial cells. However, the existence of a significant sinusoidal ne twork in the human heart is doubtful. Whether the myocardium can be perfuse d directly via the TMR channels is controversial; it is becoming clear that other mechanisms such as angiogenesis are also at work. This review will u se TMR as an example to illustrate how surgical practice and thinking can b e based on theories that have little or no sound experimental evidence to s upport them. The importance of elucidating the valid scientific basis of su rgical procedures in this modern era of evidence-based medicine will be emp hasized.