Contact Force Increases During Radiofrequency Ablation: A Novel Catheter Assessment of Myocardial Response to Thermal Injury.

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Contact force (CF) changes after onset of radiofrequency (RF) delivery are not well understood and often ascribed to catheter instability. This study sought to characterize CF changes during RF-based pulmonary vein (PV) isolation. Catheter-tip parameters including CF for all RF sessions were extracted from a novel catheter-mapping system from 6 patients undergoing PV isolation. Of a total 416 RF sessions, 241 demonstrated progressive increases in CF during RF delivery (group 1). Zero to 5 seconds of RF delivery demonstrated the greatest increase in CF, with no differences between right and left PV sites (2.2 ± 2.2 vs 1.9 ± 2.3 g, P=0.26). Subsequent 5-second intervals demonstrated greater increases for right vs left PV sites (eg, 1.2 ± 1.3 vs 0.5 ± 0.3 g, P=0.01 for 20 to 25 seconds). CF increment was greater for posterior vs anterior PV sites (3.4 ± 3.1 vs 1.4 ± 1.4 g, P< 0.001), but similar for roof and floor sites. Higher power and greater impedance drops were associated with greater CF increases. Perpendicular contact had greater CF increases, followed by diagonal and parallel contact. The remaining 175 of 416 sessions demonstrated at least 1 CF decrement, typically occurring after 15 seconds of RF (group 2). This was observed least frequently at inferior PV sites. Except for minor differences in power, there were no differences in CF, tip excursion, and impedance drop between groups. Progressive CF increase during RF ablation is a distinct phenomenon that likely reflects the "push-back" effect of local myocardial swelling against the catheter tip. This may explain certain catheter-tip behaviors such as tip displacement and instability during ablation.