A Rewarming Maneuver Demonstrates the Contribution of Blood Flow to Electrode Cooling During Internally Irrigated RF Ablation

INTRODUCTION: Titration of radiofrequency (RF) ablation energy to avoid steam pops while maximizing lesion size is difficult because of disparities between electrode and tissue temperature. We hypothesized that the variable contribution of local blood flow to electrode cooling contributes to electrode-tissue temperature disparity, even with an irrigated RF catheter. METHODS AND RESULTS: Forty RF lesions were made in the atria of live swine with an internally irrigated cooled RF catheter. Prior to RF delivery, the catheter tip was cooled and then allowed to rewarm to body temperature by stopping irrigant flow. The rewarming time (RT) was noted. The catheter was again cooled and RF energy delivered, with power titrated to achieve electrode temperature of 40 degrees C, which was previously defined as the approximate upper limit of safety. Lesion formation and steam pops were observed with intracardiac echocardiography. The RT ranged from 10 to 47 seconds. Nine steam pops were seen. The mean RT for lesions with pops was faster than those without (20 vs. 33 seconds, P = 0.003). The 20 lesions with faster RT required more power to achieve target temperature than the 20 lesions with slower RT (P = 0.01). Eight of nine steam pops occurred in the group with faster RT. CONCLUSIONS: RT quantifies convective heating by blood prior to RF. Faster RT predicts greater cooling by blood during irrigated RF, a greater power requirement to reach target electrode temperature, and a higher risk of steam pops during fixed-temperature ablation. RT therefore can demonstrate the variation in blood cooling with each lesion and can be used to tailor energy delivery to maximize efficacy and safety.