Effects of isoproterenol and propranolol on the inducibility and frequency of ventricular fibrillation in patients with Brugada syndrome.

Background: Isoproterenol (ISP), a beta-adrenergic agonist, suppresses arrhythmic storm in patients with sporadic Brugada syndrome (BS). However, the influence of ISP and the beta-adrenergic antagonist propranolol (PRO) on the inducibility and frequency of ventricular fibrillation (VF) in BS patients remains unclear.

Methods And Results: Twenty-seven BS patients with induced VF>10s in a control state were enrolled. Electrophysiological stimulation (EPS) testing was performed during ISP and after PRO in selected patients. The inducibility and frequency of VF were compared. Dominant frequency (DF) was obtained by Fast Fourier transform from 4-s data (phase) and sequentially every 2s up to phase 5. ISP prevented induction of VF in 20 of 25 patients (80%). During ISP, 5 patients experienced induction of VF. ISP significantly influenced DF transition compared with the control state. DF gradually increased but was unchanged after the middle phase. PRO had no effect on incidence of induced VF in 5 patients; increased PRO induced VF in 5 (83.3%) of 6 patients who tested negative during ISP. After PRO, 10 patients experienced induction of VF. Thus, PRO significantly influenced DF transition. DF after PRO was higher than that in the corresponding phase in the control state.

Conclusion: ISP suppressed induction of VF and the increase of DF with time. PRO aggravated VF and accelerated DF.