Higher contact force, energy setting, and impedance rise during radiofrequency ablation predicts charring: New insights from contact force-guided in vivo ablation

Introduction: Higher contact force (CF) theoretically increases the risk of blood charring, diminishing lesion formation. We aimed to investigate the relationship between CF, impedance change, and char formation during pulmonary vein isolation (PVI). Methods: CF was assessed during PVI in 65 patients. Radiofrequency ablation (RFA) with power-controlled mode was applied in the point-by-point manner. The RFA were divided into five groups: group A (CF < 10 g), group B (10 g <= CF < 20 g), group C (20 g <= CF < 30 g), group D (30 g <= CF < 40 g), and group E (CF >= 40 g). Gradual impedance rise (gIR) was defined as > 5 Omega increase during each 10-second period of RFA. Catheter tip was assessed for charring during, and at the end of each procedure. Results: In total, 2,064 applications were analyzed. During 0-10 seconds, impedance was significantly decreased in groups with higher CF (P < 0.05). During 10-20 seconds, an impedance decrease was not significantly different among the five groups. During 20-30 seconds, mean impedance increased in group E. AgIR was noted at least once during RFA in 63 patients (97%). The incidence of gIR during RFA after 20 seconds was significantly higher in groups D and E (77/504 [15.3%] vs. 90/1560 [5.8%], P < 0.001). Charring occurred in 8 of 65 (12%) patients. A gIR after 20 seconds was significantly associated with a higher incidence of macroscopic charring (6/20 [30%] vs. 2/45 [4%], P < 0.01). Conclusions: gIR was noted with higher applied CFs after 20 seconds of RFA. This impedance rise may be avoided by keeping the applied CF under 26.9 g with negative predictive value of 95%. Our data suggested that g IR may be related to the incidence of charring.