INVERSE RELATIONSHIP BETWEEN ELECTRODE SIZE AND LESION SIZE DURING RADIOFREQUENCY ABLATION WITH ACTIVE ELECTRODE COOLING

Background-Clinical efficacy has driven the use of larger electrodes ( 7F, length greater than or equal to 4 mm) for radiofrequency ablation, which reduces electrogram resolution and causes variability in tissue contact depending on electrode orientation. With active cooling, abla tion electrode size may be reduced. The purpose of this study was to e xamine the effect of electrode length on tissue temperature and lesion size with saline irrigation used for active cooling: Methods and Resu lts-In 11 anesthetized dogs, the thigh muscle was exposed and bathed w ith heparinized canine blood. A 7F ablation catheter with a 2- or 5-mm irrigated tip electrode was positioned perpendicular or parallel to t he thigh muscle. Radiofrequency current was delivered at constant volt age (50 V) for 30 seconds during saline irrigation (20 mL/min) to 148 sites. Tissue temperature at depths of 3.5 and 7 mm and lesion size we re measured. In the perpendicular electrode-tissue orientation, radiof requency applications at 50 V with the 2-mm electrode compared with th e 5-mm electrode resulted in lower power at 50 V (26 versus 36 W) but higher tissue temperatures, larger lesion depth (8.0 versus 5.4 mm): a nd greater diameter (12.4 mm versus 8.4 mm). Also, in the parallel ori entation, overall bower was lower with the 2-mm electrode (25 versus 3 3 W), but tissue temperatures were higher and lesions were deeper (7.3 versus 6.9 mm). Lesion diameter was similar (11.1 versus 11.3 mm) for both electrodes. Conclusions-The smaller electrode resulted in transm ission of a greater fraction of the radiofrequency power to the tissue and resulted in higher tissue temperature, larger lesions, and lower dependency of lesion size on the electrode orientation.