Electrophysiological efficacy of Epicor high-intensity focused ultrasound

Objectives: Clinical success of atrial fibrillation (AF) ablation depends on persistent blocking of electrical conduction across the ablation lines. Epicor high-intensity focused ultrasound (HIFU) ablation has been credited with a variable clinical efficacy. The aim of this work is to ascertain the electrophysiological (EP) efficacy of such lesions, by assessing pulmonary vein isolation (PVI) after open chest HIFU ablation, in the clinical setting. Methods: Ten consecutive mitral patients (mean age: 57 ± 10 years) with paroxysmal AF undergoing concomitant ablation with the Epicor ablation system (St. Jude Inc.®, Minneapolis, MN, USA) were enrolled for EP assessment. During surgery, pairs of additional temporary wires were positioned on the right PVs (RPVs) and on the roof of the left atrium (RLA), before epicardial ablation. Exit block (no capture during PV pacing) of RPV and of RLA was assessed before, after ablating and immediately after closure of the chest, in order to check the correct positioning of the wires. EP assessment was repeated before discharge and at 3 weeks. Results: Baseline RPV pacing threshold (PT) was 3.5 ± 2 mA (range 1.5-8), of RLA 1.73 ± 1.1 mA (range 0.7-4.3 mA). PVI was not reached any time after HIFU ablation. At the pre-discharge EP study, the absence of isolation was observed in all cases. At 3 weeks, the PTs were 6.8 ± 5.8 mA on RPV (range 2-16) and 6.4 ± 5.3 mA (range 1-19) on RLA. All patients were discharged in sinus rhythm. CONCLUSIONS: PVI was not achieved after Epicor HIFU ablations, up to 3 weeks after surgery.