Locations of high contact force during left atrial mapping in atrial fibrillation patients: Electrogram amplitude and impedance are poor predictors of electrode-tissue contact force for ablation of atrial fibrillation

Background-During radiofrequency ablation, high electrode-tissue contact force (CF) is associated with increased risk of steam pop and perforation. The purpose of this study, in patients undergoing ablation of paroxysmal atrial fibrillation, was to: (1) identify factors producing high CF during left atrial (LA) and pulmonary vein mapping; (2) determine the ability of atrial potential amplitude and impedance to predict CF; and (3) explore the feasibility of controlling radiofrequency power based on CF. Methods and Results-A high-density map of LA/pulmonary veins (median 328 sites) was obtained in 18 patients undergoing atrial fibrillation ablation using a 7.5-Fr irrigated mapping/ablation catheter to measure CF. Average CF was displayed on the 3D map. For 5682 mapped sites, CF ranged 1-144 g (median 8.2 g). High CF (≥35 g) was observed at only 118/5682 (2%) sites, clustering in 6 LA regions. The most common high CF site (48/113 sites in 17/18 patients) was located at the anterior/rightward LA roof, directly beneath the ascending aorta (confirmed by merging the CT image and map). Poor relationship between CF and either unipolar amplitude, bipolar amplitude, or impedance was observed. During ablation, radiofrequency power was modulated based on CF. All pulmonary veins were isolated without steam pop, impedance rise, or pericardial effusion. Conclusions-High CF often occurs at anterior/rightward roof, where the ascending aorta provides resistance to the LA. Atrial potential amplitude and impedance are poor predictors of CF. Controlling radiofrequency power based on CF seems to prevent steam pop and impedance rise without loss of lesion effectiveness.