BackgroundAcutely effective repeat radiofrequency catheter ablation (RFCA) after previous atrial fibrillation ablation depends on several parameters including local impedance (LI), contact force (CF) and power. ObjectiveTo investigate the relationship of LI, CF and power to the LI drop in a repeat atrial RFCA environment. MethodsConsecutive patients undergoing repeat atrial RFCA were studied. High-quality local electrograms (EGMs) were analyzed regarding morphology changes indicating effective RFCA and associated LI dynamics. The influence of baseline LI, mean CF and power on the LI drop was analyzed. Investigated power levels included ≤25 W, 30 W and ≥40 W. Results1390 RFCA points from 48 patients (48 % female, median age 70 years) were analyzed. 40.5% of 309 analyzed EGMs showed effective RFCA morphology changes with a higher median LI drop (effective 19.7 Ω vs partially effective 14.1 Ω, p<0.001). CF showed the highest correlation to the LI drop within high baseline LI and when applying ≥40 W (low baseline LI, R=0.39; intermediate, R=0.66; high, R=0.72). Within low baseline LI regions, CF levels showed a lower correlation to the LI drop (≤25 W, R=0.30; 30 W, R=0.35; ≥40 W, R=0.39). A mean CF ≥10 g resulted in elevated LI drops with higher power compared to lower power within all baseline LI tertiles (p<0.001 each). ConclusionWithin rather high baseline LI regions, CF plays a greater role for the maximum LI drop when higher power is chosen. A mean CF ≥10 g ensures increased LI drops with increasing power levels.