Catheter tip orientation affects radiofrequency ablation lesion size in the canine left ventricle.

While some factors influencing size of RF lesions in ventricular tissue have been characterized, the effects of catheter electrode-endocardial surface orientation on lesion generation have not been investigated. Therefore, the effects of parallel versus perpendicular catheter electrode-endocardial surface orientation on dimensions of RF lesion produced with 4-, 6-, 8-, 10-, and 12-mm distal electrode lengths were studied in 20 closed-chested dogs. Orientation was established by biplane fluoroscopy and confirmed by intracardiac echocardiography for the majority of energy deliveries (71%). RF voltage was titrated to maintain constant catheter electrode temperature of 75 degrees C for 60 seconds. In the perpendicular orientation, lesion size did not change significantly with increasing electrode lengths. There was a statistically significant interaction between electrode orientation and maximum lesion length (analysis of variance [ANOVA] P = 0.04], lesion width (ANOVA P = 0.01), lesion area (ANOVA P = 0.02), and estimated lesion volume (ANOVA P < 0.005) over all electrode lengths. With parallel tip-tissue orientation, lesion size was a function of increasing electrode length. For 4-, 6-, 8-, 10-, and 12-mm electrodes, maximum lesion surface areas were 95 +/- 38, 97 +/- 38, 119 +/- 29, 147 +/- 52, and 147 +/- 67 mm2, respectively. For electrode lengths 8, 10, and 12 mm, estimated lesion volumes were significantly greater with parallel orientation (P < 0.05 for all). Thus, ventricular lesion size is dependent on catheter electrode length, but only when the catheter is oriented parallel to the endocardial surface. This information may be helpful in increasing lesion dimensions for RF ablation of ventricular tachycardias.