Characterization of Catheter–Tissue Contact Force During Epicardial Radiofrequency Ablation in an Ovine Model

BACKGROUND: Contact force (CF) during radiofrequency ablation (RFA) is an important determinant of endocardial lesion size with limited data on epicardial RFA and CF. We evaluated CF characteristics using irrigated RFA on the epicardium in an ovine model. METHODS AND RESULTS: In 12 sheep, a 7-F irrigated RFA catheter with CF sensor was introduced via a pericardial incision onto/in parallel with ventricular epicardium. RFA (30 W per 30 second duration) was applied at 5g, 10g, 20g, 40g, and 70g: (1) over left and right ventricular myocardium with or without fat, (2) either directly over or adjacent to a coronary artery, or directly over the phrenic nerve. Force-time integral, lesion dimensions, and coronary artery/phrenic nerve injury were recorded. Lesion size, volume, and force-time integral progressively increased with higher CF (P<0.05). Steam pops occurred with high CF. Epicardial fat had an attenuating effect on RF penetration into myocardium (P<0.05); however, myocardial RF lesions could be created at sites with >3.5 mm epicardial fat. At sites with epicardial fat, each 10g increment in CF led to a 0.6 mm increase in lesion depth, whereas each 1 mm of fat reduced lesion depth into underlying myocardium by 0.7 mm. Extent of acute coronary injury with direct and indirect RFA and phrenic nerve palsy occurrence was proportional to CF. CONCLUSIONS: CF is a determinant of epicardial RF lesion size, steam pops, acute coronary artery injury, and phrenic nerve injury. Although epicardial fat limits lesion size, RFA with high CF can produce small myocardial RF lesions at sites of thick epicardial fat.