Advanced radiofrequency catheter ablation in canine myocardium.

Current radiofrequency (RF) ablation technology is limited by small lesion size. To enhance the size of RF-induced left ventricular (LV) endocardial lesions, we evaluated the effects of an enlarged distal electrode tip and increased RF power on lesion volume. Steerable electrode catheters with distal electrode tips of 4 to 12 mm were studied in anesthetized dogs at power settings of 20 to 100 W. Temperature was continuously 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 nitroblue tetrazolium. Lesion area was planimetered and volume was calculated. Lesion volume increased with increasing electrode size and delivered 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 tip (914 +/- 362 mm3 vs 460 +/- 150 mm3, 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 measured 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 tachycardia may be enhanced by this technology.