Convective cooling effect on cooled-tip catheter compared to large-tip catheter radiofrequency ablation

Background. Both actively cooled-tip and large-tip catheters are currently available clinically to create large endomyocardial lesions during application of radiofrequency (RF) energy. The purpose of this study was to compare the effect of convective cooling at physiologic flow rates on RF lesion size using both actively cooled and large-tip catheters. Methods. Porcine hearts were sectioned into 72 pieces and placed in a temperature-con trolled saline both (37 degrees C) with varying directed flow rates (0, 1, 2, and 3 L/min). Cooled-tip RF ablation (4 mm tip) was performed for 1 minute on 36 tissue sections with power manually titrated to keep tip temperature below 40 degrees C. Large-tip catheter ablation (10 mm tip) was performed at 65 degrees C target temperature for 1 minute on 36 tissue sections. For each catheter, flow rates were randomized between applications. The tissue pieces were sectioned and measured to determine lesion depth, width, and volume. Results. Lesion dimensions were independent of the flow rate for the cooled-tip catheter (mean volumes: 382.0 +/- 121.6, 419.9 +/- 133.4, 375.9 +/- 169.1, and 346.7 +/- 173.4 mm(3) for 0, 1, 2, and 3 L/min flow rate, respectively, P = 0.78). For the large-tip catheter, lesion size varied significantly with flow, such that higher flow rates produced larger lesions (mean volumes: 120.7 +/- 50.7, 256.5 +/- 97.9, 393.4 +/- 149.9, and 548.9 +/- 157.0 mm(3) for 0, 1, 2, and 3 L/min flow rate respectively, P < 0.001) Conclusion. During RF ablation, blood flow rate significantly affects lesion size for large-tip but not cooled-tip catheters. At low flow rates (0-1 L/min) cooled-tip catheters create larger lesions, while at high flow rates (3 L/min) large-tip catheters create larger lesions.