Neodymium:YAG laser photocoagulation (LPC) is an investigational technique for the treatment of drug-resistant postinfarction ventricular tachycardia that requires cardiopulmonary bypass and open heart surgery. The purpose of this experimental study was to evaluate the feasibility of contact epicardial LPC to reach subepicardial, deep myocardial, and subendocardial regions without ventriculotomy and to analyze the dose-response relationships of this new technology. In 24 open-chest, closed heart dogs, a total of 219 epicardial laser lesions were generated under sterile conditions. Laser source was a continuous wave 1064 nm Nd:YAG; the delivery system consisted of a 400 mu bare quartz fiber fed into an 8F electrode catheter in direct contact with the epicardial surface. Laser variables were power at 10-15-20 W; lasing time, 6-12-18-24 s; lasing mode, continuous and pulse-pause; fiber mode, optical fiber tip inside and extending out from the electrode catheter. Hearts were harvested at 1 week. Histologic measurements included lesion surface diameter, internal diameter, and depth.
Results: Significant linear correlation was found between the total delivered energy and all measured lesion parameters. Transmural lesions were found at energy levels of 270-480 J. Maximum depth measured up to 1.68 cm; at high energies, it was limited by myocardial thickness only. At constant energy levels, power and lasing time did not independently affect lesion dimensions; lasing mode and fiber mode had statistically significant but minor effects. Laser lesions were homogeneous and sharply demarcated without epicardial crater or endocardial thrombus formation. Endocardial surface cooling by circulating blood and the presence of epicardial vessels resulted in modifications in lesion morphology. In 29 out of 74 grossly transmural lesions, there was a 0.082 +/- 0.127 cm thin surviving subendocardium. Forty-five coagulation lesions were truly transmural with no surviving myocardial strands. In conclusion, contact epicardial LPC can result in deep, transmural myocardial coagulation lesions. Lesion dimensions can be adequately controlled by total delivered energy. Closed heart epicardial Nd:YAG laser photocoagulation could become a new, less invasive surgical technique for the treatment of drug-resistant ventricular tachycardia.