Vagal response is involved in the occurrence of ventricular fibrillation in patients with early repolarization syndrome

BACKGROUND Patients with early repolarization syndrome (ERS) and Brugada syndrome (BruS) have comparable clinical symptoms. In both conditions, ventricular fibrillation (VF) is experienced often near midnight or in the early morning hours when the parasympa-thetic tone is augmented. However, differences between ERS and BruS regarding the risk of VF occurrence have recently been re-ported. The role of vagal activity remains especially unclear.OBJECTIVE The goal of this study was to determine the relation-ship between VF occurrence and autonomic nervous activity in patients with ERS and BruS.METHODS We enrolled 50 patients with ERS (n = 16) and BruS (n = 34) who received an implantable cardioverter-defibrillator. Of these, 20 patients (5 ERS and 15 BruS) experienced VF recurrence (recurrent VF group). We investigated baroreflex sensitivity (BaReS) with the phenylephrine method and heart rate variability using Holter electrocardiography in all patients to estimate autonomic nervous function. RESULTS In both patients with ERS and BruS, there was no signif-icant difference in heart rate variability between the recurrent VF and nonrecurrent VF groups. However, in patients with ERS, BaReS was significantly higher in the recurrent VF group than in the nonre-current VF group (P = .03); this difference was not evident in pa-tients with BruS. High BaReS was independently associated with VF recurrence in patients with ERS according to Cox proportional hazards regression analyses (hazard ratio 1.52; 95% confidence in-terval 1.031-3.061; P = .032).CONCLUSION Our findings suggest that in patients with ERS, an exaggerated vagal response, as represented by increased BaReS indices, may be involved in the risk of VF occurrence.