Mechanisms and Results of Transmyocardial Laser Revascularization

Transmyocardial Revascularization: Peril and Potential

Transmyocardial laser revascularization is a technique for the treatment of patients with chronic angina pectoris that is refractory to medical therapy and who are not eligible for surgical intervention. Percutaneous myocardial revascularization is a less-invasive catheter-based procedure that has been adapted from transmyocardial laser revascularization. Six prospective randomized clinical trials have been performed with transmyocardial laser revascularization and 5 have been performed using percutaneous myocardial revascularization. All of the transmyocardial laser revascularization and 4 of the percutaneous myocardial revascularization studies showed a significant improvement in angina class; however, results for improved survival, increased exercise tolerance, improved ejection fraction, and improved myocardial perfusion were less definitive. Transmyocardial laser revascularization has significant potential for morbidity and mortality. This article summarizes the results of the randomized trials, explains the current theories for the mechanism of transmyocardial laser revascularization, and discusses its current role in treatment for patients, considering the evidence that currently exists.

Does laser type impact myocardial function following transmyocardial laser revascularization?

BACKGROUND

Transmyocardial laser revascularization (TMR) is currently clinically performed with either a CO(2) or Ho:YAG laser for the treatment of severe angina. While both lasers provide symptomatic relief, there are significant differences in the laser-tissue interactions specific to each device that may impact their ability to enhance the perfusion of myocardium and thereby improve contractile function of the ischemic heart.

METHODS

A porcine model of chronic myocardial ischemia was employed. After collecting baseline functional data with cine magnetic resonance imaging (MRI) and dobutamine stress echo (DSE), 14 animals underwent TMR with either a CO(2) or Ho:YAG laser. Transmural channels were created with each laser in a distribution of 1/cm(2) in the ischemic zone. Six weeks post-treatment repeat MRI as well as DSE were obtained after which the animals were sacrificed. Histology was preformed to characterize the laser-tissue interaction.

RESULTS

CO(2) TMR led to improvement in wall thickening in the ischemic area as seen with cine MRI (40.3% vs. baseline, P < 0.05) and DSE (20.2% increase vs. baseline, P < 0.05). Ho:YAG treated animals had no improvement in wall thickening by MRI (-11.6% vs. baseline, P = .67) and DSE (-16.7% vs. baseline, P = 0.08). Correlative semi-quantitative histology revealed a significantly higher fibrosis index in Ho:YAG treated myocardium versus CO(2) (1.81 vs. 0.083, P < 0.05).

CONCLUSIONS

In a side-by-side comparison CO(2) TMR resulted in improved function of ischemic myocardium as assessed by MRI and echocardiography. Ho:YAG TMR led to no improvement in regional function likely due to concomitant increase in fibrosis in the lasered area.

Method for inducing the growth of new arteries in the myocardium

OBJECTIVE

The creation of new coronary arteries has long been an objective of cardiac research. I describe a method for creating new blood vessels in the myocardium of the left ventricular wall in animals.

METHODS

The myocardium was pierced by a fistula. Then a biodegradable hydrogel fiber with antithrombogenic and nonadhesive properties was inserted into the fistula with a venous catheter. Nine dogs were used. Three fibers were inserted in each heart, and two additional punctures were made and left empty as controls.

RESULTS

During absorption of the fiber, the luminal surface of the fistula became lined with endothelial cells and developed many openings to capillary blood vessels of the myocardium naturally. Three straight fibers were inserted so they intersected in the myocardium. They created a new branched vessel. The fistulas had connections to original coronary arteries and worked as new arteries to supply blood to the area where they were created.

CONCLUSIONS

It was possible to create new blood vessels in the myocardium in animals.