In vivo temperature measurement during transcatheter endomyocardial Nd-YAG laser irradiation in dogs.

Intramural temperatures were monitored during catheter-directed endomyocardial non-contact laser irradiation by means of an array of thermocouples inserted epicardially. Via a novel electrode-laser catheter, a total of 30 Nd-YAG laser pulses, 1064 nm, 25 W/15 s, 20 W/30 s, 15 W/45 s,n = 10 each, were aimed at various endocardial sites in the ventricles of four dogs. Temperatures increased gradually after the onset of the laser pulses. Maximum values were measured in the central area of the irradiated spots: 100 +/- 15 double daggerC at 25 W, 78+/- 23 double daggerC at 20 W and 80 +/- 13 double daggerC at 15 W. Application of 300 J of laser energy induced significantly higher temperatures at 25 W (p< 0.02) than at 20 or 15 W (20vs 15 W: p> 0.05). Initial temperature rise and lesion formation was accompanied by dwindling of local electrical potentials. There was no crater formation. Transcatheter non-contact Nd-YAG laser coagulation of healthy ventricular myocardium can be performed in a safe and controllable manner at power settings up to 20 W and laser energies up to 675 J.