Intra-operative RF ablation in the atria

We examined two methods of creating atrial linear transmural lesions for an epicardial approach. In a monopolar approach, radiofrequency (RF) ablation was applied to a multiple coil electrode probe with internal cooling to create linear and transmural lesions from the epicardium. Compared to no cooling, internal cooling enables faster and deeper lesion formation. In vitro experiments showed that with internal cooling epicardial RF energy applications time requirements could be reduced from longer than 3 min to 45 seconds to achieve transmural lesions despite convective endocardial cooling produced by blood flow. In vivo experimentation in five sheep confirmed atrial transmural lesions were achieved using 120 seconds of RF application times at set temperatures of 80°C. In a bipolar clamp approach, RF ablation was applied from multiple coil electrodes mounted on one jaw of the clamp to coil electrodes mounted on the opposing jaw of the clamp. In vitro experiments showed that lesions could be made reliably through tissues up to 1-cm thick using RF energy applied for 30 seconds with a set temperature of 80°C. Animal experiments confirmed that pulmonary veins (PV) could be isolated in an electrophysiological (EP) sense from the left atrium by creating an encircling lesion in a cuff of tissue surrounding the PV using the bipolar ablating clamp technique.