Area under the real-time contact force curve (force-time integral) predicts radiofrequency lesion size in an in vitro contractile model.

Introduction: Electrode tissue contact, radiofrequency (RF) power and duration are major determinants of RF lesion size. Since contact forces (CF) vary in the beating heart, we evaluated contact force-time integral (FTI) as a predictor of lesion size at constant RF power in a contractile bench model simulating the beating heart.

Methods And Results: An open-tip irrigated catheter was attached to a movable mount incorporating a dynamic force sensor allowing closed loop control to achieve desired force variations between the catheter tip and bovine skeletal muscle placed on a ground plate. RF energy (20 and 40 W for 60 seconds, 17 cc/min irrigation) was delivered during (1) constant contact (C) at 20 g, (2) variable contact (V) with a 20 g peak and 10 g nadir, and (3) intermittent contact (I) with a 20 g peak and 0 g nadir with loss of contact. V and I protocols were performed at 50 and 100 catheter movements/min and 2 systole:diastole time ratios (50:50 and 30:70). The area under the CF curve was calculated as the FTI. Measured FTI was highest in C, intermediate during V and lowest during I and correlated linearly with lesion volume (P < 0.0001 for 20 and 40 W). Lesion volume was highest in group C, intermediate in V and lowest in group I (P < 0.05 for C vs V, V vs I, and C vs I).

Conclusions: Lesion size correlates linearly with measured contact FTI. Constant contact produces the largest and intermittent contact the smallest lesions despite constant RF power and identical peak contact forces.