Electrophysiology Study and Ablation
Patients were taken to the electrophysiology laboratory in the fasting, postabsorptive state. The level of anesthesia was determined by the performing electrophysiologist. Intravenous prophylactic antibiotics were administered. Following vascular access, intravenous heparin was administered to achieve activated clotting time (ACT) of 300-350 seconds. An arterial line was placed for continuous blood pressure monitoring. A 5 French (Fr) quadripolar catheter was placed in the right ventricular apex and a 7 Fr decapolar catheter was placed in the coronary sinus. Intracardiac echocardiography (ICE, Acuson, Siemens, Germany) was used as standard to assist mapping/ ablation and assess for complications. Left ventricular (LV) access was obtained by anterograde trans-septal or retrograde trans-aortic approach. 3-dimensional electroanatomical mapping (CARTO, Biosense Webster, Diamond Bar, CA) was used in all patients. Mapping was performed in point-by-point fashion using an externally irrigated ablation catheter (THERMOCOOL® Biosense Webster, Diamond Bar, CA). For VTs, programmed ventricular stimulation and burst pacing were utilized for induction. For PVCs, burst pacing was favored if PVCs were scarce. Isoproterenol was utilized as needed for both. Standard mapping techniques were used to identify ablation targets.17 In the case of PVCs, activation and pace mapping was predominantly utilized. In VT cases, entrainment and activation mapping were used if the arrhythmia was hemodynamically tolerated. With unstable VT, pace and substrate mapping were favored. Scar-related reentry was defined as the VT mechanism when VT was inducible with programmed stimulation and when entrainment could be demonstrated. VT was considered involving the perimitral area in cases where abnormal electrograms and critical sites responsible for VT were identified within 2 cm of the valve annulus. Ablation energy was typically started at 30 W and up-titrated as necessary, up to a maximum limit of 50 W.