[Experimental studies on the effects of Nd;YAG laser photocoagulation of arrhythmogenic foci].

Cryosurgical ablation of arrhythmogenic foci is an established operative method for arrhythmia surgery. Cryothermal lesion is characterized as well-demarcated fibrous scar without thinning in the chronic phase and having no tendency of inducing arrhythmias in itself. Recently, LASER ablation for the treatment of cardiac arrhythmias has emerged as a new technique. We investigated the implications of LASER delivery to myocardium with Nd;YAG LASER system and examined if LASER ablation could make the same characteristic lesion as that achieved with cryosurgical application to canine's myocardium. Nine mongrel dogs were used in this experiment. Seven dogs were examined in the acute phase and two in the chronic phase of LASER ablation. Under general anesthesia, right thoracotomy and pericardiotomy were performed. Then Nd;YAG LASER was delivered onto the epicardial surface with our new device and on atrioventricular groove after dissection of epi-annular fat pad. The tip of the LASER fiber was positioned about 5 mm above the cardiac surface and LASER power of between 10 and 50 Watts was used with the varied duration of lasers 3 and 20 seconds. Histologically, the nature of the lesion in the acute phase showed a well-demarcated area of heat denaturation consisted of coagulation necrosis and contraction band necrosis, and surrounded by a narrow area of edematous myocardium around that lesion, which changed to a fibrous scar in the chronic phase completely. There was a good correlation (r = 0.79; p less than 0.01) between the lasers energy and the depth of the lesion. Any arrhythmia was not induced by post-emission programmed ventricular stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)