Introduction Bipolar (BIP) radiofrequency (RF) ablation creates deep myocardial lesions but ideal energy application modes to treat ventricular arrhythmias originating from deep inside the thick myocardium have not been well established. An experimental study was performed to clarify whether high power and long application time BIP ablation were performable by impedance‐decline‐guide power control (PC) and whether it could create transmural lesions in the thick ventricle with a minimum risk of steam‐pop. Methods and Results Perfused porcine ventricle (18.4 ± 2.3 mm) was placed in an experimental bath and BIP ablation (50 W) for 120 s was attempted with catheter contact of 30‐g using two protocols; fixed power (FP) and impedance‐decline‐guide PC. In the latter protocol, BIP ablation was started from 50 W, while the energy was decreased to 40–20 W according to the impedance decline during RF ablation. FP ablation was attempted in 30 applications and the transmural lesion was created in all 30, although steam‐pop occurred in 16/30 applications (53%). Low minimum impedance, large total impedance decline (TID), and %‐TID were associated with the steam‐pop occurrence. PC ablation was attempted in another 21 applications, and the transmural lesion was created in all 21 without steam‐pop. PC ablation was superior to FP ablation (21/21 vs. 14/30, p < .001) in the creation of a transmural lesion without resulting in steam‐pop. Conclusions High power and long application time BIP ablation seems to be feasible according to the impedance‐decline‐guide approach, which could create transmural lesions in thick porcine ventricles with minimal risk of steam‐pop.

Introduction Radiofrequency (RF) catheter ablation induces excitation recoverable myocardium around durable core lesions, and its distribution may be different depending on energy delivery methods. Methods and Results In coronary perfusing porcine hearts, pacing threshold through the ventricle was measured using eight‐pole (1‐mm distance) needle electrodes vertically inserted into myocardium before, within 3 min after and 40 min after 40 W ablation with 10‐g catheter contact (Group 1: irrigation catheter for 15 s, Group 2: irrigation catheter for 40 s, Group 3: nonirrigation catheter for 15 s, Group 4: nonirrigation catheter for 40 s). Ablation was accomplished in all 12 ablations in Groups 1–3 whereas in 8/12 ablations in Group 4 because of high‐temperature rise. Within 3 min after ablation, 10.0 V pacing uncaptured electrodes were distributed from the surface to inside the myocardium, and its depth was deeper in 40 s than in 15 s ablation. 40 min after ablation, excitation recovery at one or more electrodes below the durable lesion was observed in all Groups. Excitation recovery electrodes were also observed on the surface in Group 1 but not the other Groups. Accordingly, the number of excitation‐recovered electrodes were larger in Group 1 than the other Groups. Conclusions Regardless of the ablation methods, excitation recoverable myocardium was present around 1.0 mm below the durable lesions. Lesions created by short application time using an irrigation catheter may have included large excitation recoverable myocardium soon after ablation because of the presence of reversible myocardium on well‐irrigated myocardial surfaces.

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