Exploring the scientific basis of surgery: transmyocardial revascularization

Transmyocardial revascularization (TMR) is a new surgical procedure aimed at increasing blood flow to the ischemic myocardium. It has been used for treatment of patients with end-stage coronary artery disease who are not candidates for conventional measures such as medication, percutaneous transluminal coronary angioplasty, and coronary artery bypass grafting. TMR involves creating transmural channels in the myocardium using lasers, in areas shown to be ischemic during preoperative testing. This procedure has shown promising results in clinical trials, but the mechanism of its efficacy remains largely unknown. TMR was originally developed as a means of supplying blood to the ventricular myocardium, directly through channels made in the wall of the ventricle. This was in an attempt to recreate the situation that exists in the reptilian heart, in which the myocardium is perfused directly from the ventricular chamber through a rich network of sinusoids that bathe the myocardial cells. However, the existence of a significant sinusoidal network in the human heart is doubtful. Whether the myocardium can be perfused directly via the TMR channels is controversial; it is becoming clear that other mechanisms such as angiogenesis are also at work. This review will use TMR as an example to illustrate how surgical practice and thinking can be based on theories that have little or no sound experimental evidence to support them. The importance of elucidating the valid scientific basis of surgical procedures in this modern era of evidence-based medicine will be emphasized.