Nademanee et al reported nine symptomatic patients with BrS
Nademanee et al. reported nine symptomatic patients with BrS who experienced VF and underwent electrophysiological study and catheter ablation . The patients exhibited abnormal epicardial electrograms characterized by fragmented electrograms with a relatively low voltage (<1mV), prolonged duration, and fractionated late potentials exclusively localized over the anterior aspect of the RVOT epicardium. Catheter ablation over these abnormal areas at the epicardial sites of the anterior aspect of the RVOT rendered the VT/VF non-inducible in seven of nine patients (78%) and normalized the Brugada ECG pattern in eight patients (89%). After a mean follow-up of 20±6 months, eight of nine patients (89%) had no recurrence of VF episodes, and there were no shocks from the ICD. Amiodarone was resumed at 100mg daily in only one patient with VF recurrence after ablation, and there were no VT/VF recurrences up to 33 months after the ablation. Thus, RVOT was suggested to be an important target for catheter ablation, as an originating site of trigger VPCs and as an arrhythmogenic substrate of VF in BrS [9–11].
Idiopathic ventricular fibrillation Idiopathic ventricular fibrillation (IVF) is generally diagnosed by exclusion of apparent structural heart disease, identifiable genetic syndromes, and any other potential causes of VF . Thus, IVF may not strictly be categorized as a channelopathy. The gold standard treatment for either primary or secondary prevention of SCD is the insertion of an ICD. Recent progress in understanding the mechanism of IVF strongly suggests that the Purkinje network [13–17] and the RVOT [15,18] play a pivotal role in both the initiation and perpetuation of VF. PVCs originating from the RVOT occasionally trigger VF although these are generally considered to be benign. Noda et al reported on 16 patients who showed spontaneous VF and/or polymorphic VTs initiated by VPCs arising from the RVOT . The optimal ablation site was determined by the earliest local activation site during the spontaneous target VPC and/or by pace mapping. Eventually, catheter ablation with a mean of 9±4 RF sirtuin inhibitors applications was successful in 13 of 16 patients and partially successful in three patients. During programmed ventricular stimulation after ablation, nonsustained polymorphic VT was induced in two patients and VF in one patient who underwent ICD implantation. During a mean-follow-up period of 54±39 months, there were no episodes of syncope, VF, or SCD (four patients received a β-blocker). The short-coupled variant of torsades de pointes (TdP) is defined as a syndrome in which VF is exhibited secondary to a short-coupled VPC (with coupling interval <300ms) without obvious heart disease or QT prolongation . The VPCs triggering VF may arise from the Purkinje network rather than RVOT or the working myocardium. Haïssaguerre et al summarized a cohort of 27 patients diagnosed as having IVF (without structural heart disease, QT prolongation, or a Brugada-like ECG) who underwent catheter ablation . In this study, VPCs originated from the Purkinje networks in 23 patients (LV septum in 10, anterior RV in nine, both in four), and from the RVOT in four patients, and the former had a shorter coupling interval initiating VF or polymorphic VT than the latter (280±26 vs 355±30ms). The interval from the Purkinje potential to the following myocardial activation varied from 10 to 150ms during premature beat but was 11±5ms during sinus rhythm. After ablation for VPCs, 24 patients (89%) without drug therapy had no VF recurrence during a 24±28 months follow-up period. The long-term prognosis of patients with IVF after catheter ablation was reported in a multicenter study . VPCs originated from the right (n=16), the left (n=14), or both (n=3) Purkinje systems, and from the myocardium (n=5) (including the RVOT [n=4]). After ablation, seven (18%) of the 38 patients (21 men, age 42±13 years) experienced VF recurrence during a median post-procedural follow-up period of 63 months. Five of these seven patients underwent repeat ablation and had no subsequent recurrence of VF or documented VPCs for 28 months. The number of significant events (confirmed VF or aborted SCD) was reduced from 4 (interquartile range 3–9) before ablation to 0 (interquartile range 0–4) after ablation (p<0.01). Taken together, short-coupled VPCs triggering VF originate predominantly from the Purkinje system and the RVOT, and catheter ablation for the triggers is feasible and is associated with long-term freedom from VF recurrence in patients with IVF.