During radiofrequency energy delivery, the catheter tip temperature can be significantly lower than the tissue temperature. The authors performed tissue temperature-controlled radiofrequency ablation in vitro and evaluated the effects of cooling, electrode to tissue contact, and target tissue temperature on lesion size. Pieces of porcine ventricle were immersed in a bath of isotonic saline solution at 37 degrees C. Radiofrequency energy was controlled by the tissue temperature as measured with a thermocouple needle placed 2 mm beneath the ablation electrode. Radiofrequency power was delivered for 30 seconds and limited to 50 W. A total of 81 radiofrequency ablations was performed with different electrode to tissue contact forces (0.04 N, 0.36 N, and 0.67 N) and target tissue temperatures (50 degrees C, 60 degrees C, and 70 degrees C) using an irrigated (27 ablations, 20 mL/min irrigation flow rate) or a nonirrigated ablation catheter. Twenty-seven nonirrigated applications were performed with fluid flow maintained by the pump of the thermostat and another 27 applications without flow. Every combination was applied three times and the average values were used for evaluation. For tissue target temperatures of 50 degrees C, 60 degrees C, and 70 degrees C, the lesion volume for nonirrigated ablations was on average 21 +/- 8 mm3, 45 +/- 23 mm3, and 109 +/- 45 mm3, respectively, and for irrigated ablations 12 +/- 7 mm3, 37 +/- 20 mm3, and 92 +/- 30 mm3, respectively. In both application groups the lesion size did not correlate with the electrode to tissue contact force. In the nonirrigated ablation group there was no difference in lesion size between the group with fluid flow and those without. Lesion size during tissue temperature-controlled radiofrequency delivery increases with increasing target tissue temperature and becomes independent of flow and electrode to tissue contact.

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