Transmyocardial laser revascularization

Abstract

It has been almost a decade since transmyocardial laser revascularization (TMR) was approved for clinical use in the United States. The safety of TMR was demonstrated initially with nonrandomized studies in which TMR was used as the only treatment for patients with severe angina. TMR efficacy was proven after multiple randomized controlled trials. These revealed significant angina relief compared to maximum medical therapy in patients with diffuse coronary disease not amenable to conventional revascularization. In light of these results, TMR has been used as an adjunct to coronary artery bypass grafting (CABG). By definition, patients treated with this combined therapy have more severe coronary disease and comorbidities that are associated with end-stage atherosclerosis. Combination CABG + TMR has resulted in symptomatic improvement without additional risk. The likely mechanism whereby TMR has provided benefit is the angiogenesis engendered by the laser-tissue interaction. Improved perfusion and concomitant improvement in myocardial function have been observed post-TMR. Additional therapies to enhance the angiogenic response include combining TMR with stem cell-based treatments, which appear to be promising future endeavors.

Fig. 1

For TMR, channels of one millimeter diameter are created in a distribution of one per square centimeter, starting inferiorly and then working superiorly to the anterior surface of the heart. The number of channels created depends on the size of the heart and on the size of the ischemic area.

Fig. 2

The CO₂ laser creates a transmural channel in a single 20J pulse. Conceptually direct perfusion may occur via the channel. Evidence indicates the laser stimulates angiogenesis in and around the channel that leads to improved perfusion.

Fig. 3

Summary of the angina relief results from five prospective randomized controlled trials comparing transmyocardial laser revascularization (TMR) and medical management (MM). Graph illustrates success rate for TMR or MM as measured by the percentage of patients that had a decrease of 2 or more angina classes. Meta-analysis of these results documents the significant advantage seen with TMR over MM.

Fig. 4

Sequential photography of the firing of a single pulse from a CO₂ laser and a Ho: YAG laser into water. The pulse duration and energy levels are the same as those employed clinically.