Intraoperative arrhythmias and tissue damage during transmyocardial laser revascularization

Background. Transmyocardial laser revascularization creates transmural channels to improve myocardial perfusion. Different laser sources and ablation modalities have been proposed for transmyocardial laser revascularization. We investigated the incidence of cardiac arrhythmias and laser-tissue interactions during transmyocardial laser revascularization of normal porcine myocardium with three different lasers. Methods. We used a continuous-wave, chopped CO2 laser (20 J/pulse, 15 s/pulse) synchronized with the R wave; a holmium:yttrium aluminum garnet (:Ho:Y(AG) laser (2 J/pulse, 250 mu s/pulse, 5 Hz); and a xenon-chloride (excimer, Xe:CI) laser (35 mJ/pulse, 20 ns/pulse, 30 Hz). Each laser was used 30 times as the sole modality in four consecutive pigs, yielding 120 channels. Results. The average number of pulses needed to create a channel was 1, 11 +/- 4,and 37 +/- 8 for the CO2 Ho:YAG, and Xe:CI lasers, respectively. All Ho:YAG and Xe:CI channels had premature ventricular contractions Ventricular tachycardia occurred in 70% of the Xe:CI and 60% of the Ho:YAG channels. Only 36% of the CO2 channels had premature ventricular contractions, and only 3% of the CO2 channels had ventricular tachycardia (p < 0.001 versus Ho:YAG and Xe:CI). Ho:YAG channels were highly irregular: each had a 0.6-mm-wide central zone surrounded by a ring of coagulation necrosis (diameter, 1.84 +/- 0.67 mm) with effaced cellular architecture in a thin hemorrhagic zone. The Xe:Cl sections exhibited the same patterns on a smaller scale (diameter, 0.74 +/- 0.18 mm). The CO, channels were straight and well demarcated. The zone of structural and thermal damage extended over half the channel's diameter, measuring 0.52 +/- 0.25 mm. Conclusions. During transmyocardial laser revascularization, the CO2 laser synchronized with the R wave is significantly less arrhythmogenic than the Ho:YAG and Xe:CI lasers not synchronized with the R wave. In addition, the interaction of the CO2 laser with porcine cardiac tissue is significantly less traumatic than that of the Ho:YAG and the Xe:Cl lasers. (C) 1999 by The Society of Thoracic Surgeons.