Nd: YAG Laser‐Photocoagulation: Acute Electrophysiological, Hemodynamic, and Morphological Effects in Large Irradiated Areas

Laser‐photocoagulation (LPC) of arrhythmogenic myocardium has been reported to successfully ablate ventricular tachycardia. The purpose of this study was to investigate the acute hemodynamic and electrophysiological effect of continuous laser energy (Nd: YAG, 1060 nm) applied via a 0.4‐mm quartz fiberoptic on the epicardial surface of the heart in nine dogs. A total of 51 ± 2.3 pulses was delivered in each animal to induce homogeneous tissue necrosis. Applied energy was 12.3 ± 2.7 J/mm2, irradiated surface measured 12.6 ± 3.0 cm2, lesion depth was 6.3 ±1.2 mm (range: 5.0–8.1 mm), lesion volume was 8.1 ± 2.8 cm3 (6.8% of left ventricular [LV] mass). After LPC, epicardial stimulation threshold significantly rose from 1.0 ± 0.3 to 10.2 ± 4.9 mA in the border zone to nontreated tissue and from 0.9 ± 0.4 to 32 ± 15.7 mA in the center of the lesions. Loss of epicardial activation in the irradiated areas could be demonstrated by epicardial mapping. Ventricular extrasystoles during LPC were seen in all dogs, ventricular tachycardia in seven, and ventricular fibrillation in two dogs. After LPC, cardiac output and LV dP/dtmax significantly decreased by 14.2% and 11.2%. LPC induced predictable homogeneous tissue edema, eosinophilic staining, contraction band necrosis, and sharp demarcated hemorrhagic border zones with a sharp electrical border zone to nontreated tissue and loss of epicardial activation. During LPC, various arrhythmogenic effects could be observed. However, no persistent arrhythmic activity developed after LPC. The results confirm the feasibility of epicardial LPC of the myocardium. Although not tested in this study, LPC of arrhythmogenic tissue may also be feasible as a treatment modality of ventricular tachycardia.