TMR has been done from both the outside and inside of the heart. When done from the outside, a laser (carbon dioxide or holmium laser) is placed in proximity to the left ventricle of the heart and sufficient energy is applied to create small channels from the outside (epicardial) surface to the inside (endocardial) surface of the heart. Thus, a number (10-50) of tiny holes are created right through the heart muscle (the myocardium). More recently, this procedure has moved into the cardiac catheterization lab and the laser works from the inside outward.
Angina is due to oxygen deprivation of the heart muscle. The channels made by the laser are intended to improve the perfusion of the oxygen-deprived heart muscle by giving it direct access to the oxygen-rich blood from the left ventricle. This does not happen for long, because the channels quickly fill with blood clot. Further, the procedure does not noticeably improve the function of the heart. Nonetheless, TMR appears to lessen or abolish the pain in patients with severe angina, at least for a while.
This procedure was originally done by heart surgery and carried an overall mortality rate of about 5 percent. The major hazards are arrhythmias (abnormal hear rhythms) and tamponade due to complete penetration of the heart. Tamponade is a life-threatening situation in which there is such a large amount of blood inside the pericardial sac around the heart that it interferes with the performance of the heart.
One-year data from three major randomized trials reported late in 1999 showed that transmyocardial revascularization (TMR), either by the open chest method or percutaneously, was superior in terms of angina relief and improvement in exercise tolerance to maximal medical therapy.