ADVANCED RADIOFREQUENCY CATHETER ABLATION IN CANINE MYOCARDIUM

Current radiofrequency (RF) ablation technology is limited by small le sion size. To enhance the size of RF-induced left ventricular (LV) end ocardial lesions, we evaluated the effects of an enlarged distal elect rode tip and increased RF power on lesion volume. Steerable electrode catheters with distal electrode tips of 4 to 12 mm were studied in ane sthetized dogs at power settings of 20 to 100 W. Temperature was conti nuously monitored from a thermistor located at the tip of the catheter . RF energy (500 kHz, unmodulated) was applied between the tip of the catheter and a large skin electrode at four separate LV sites in each animal. Hearts were excised, frozen, sectioned, and stained with nitro blue tetrazolium. Lesion area was planimetered and volume was calculat ed. Lesion volume increased with increasing electrode size and deliver ed power. However, a rise in impedance limited maximal lesion size at higher power with each electrode. Maximal lesion size with an 8 mm tip was approximately twice the size of the maximal lesion with a 4 mm ti p (914 +/- 362 mm(3) vs 460 +/- 150 mm(3), p < 0.01). Minimal lesions were seen with large tip electrodes at power <40 W because of low tip temperature (<55 degrees C). Average tip temperature correlated with m easured lesion volume (r = 0.7). ventricular fibrillation occurred in approximately one half of the animals studied, and was associated with larger lesion volume (p < 0.01). Catheter ablation of ventricular tac hycardia may be enhanced by this technology.