P351
Therapeutic inefficacy and pro-arrhythmic nature of metoprolol succinate and carvedilol therapy in patients with idiopathic, frequent, monomorphic premature ventricular contractions

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Anti-arrhythmic drugs remain the first-line therapy for treatment of idiopathic ventricular arrhythmias in clinical practice.

The aim of this study was to assess the therapeutic efficacy of extended-release metoprolol succinate (MetS) and carvedilol for idiopathic, frequent, monomorphic premature ventricular contractions (PVCs).

Study population consisted of 115 consecutive patients: 72 received MetS and 43 received carvedilol.  All patients underwent 24-hour Holter monitoring at baseline and during drug therapy.  PVC burden response to drug therapy was categorized as "Good" (≥80% reduction), "Poor" (either < 80% reduction or ≤ 50% increase) and "Pro-arrhythmic" response (> 50% increase) based on change in PVC burden compared to baseline.

Presenting symptoms were palpitations in 69 (60%), shortness of breath/chest pain/syncope in 12 (10.5%), and coincidentally discovered in 34 (29.5%) patients.  Mean MetS and carvedilol dosages were 65.57 ± 30.67 mg/day and 23.66 ± 4.26 mg/day, respectively.  "Good", "Poor" and "Pro-arrhythmic" response was observed in 13.9% and 23.3%, 61.1% and 60.5%, and 25% and 16.2% of patients treated with MetS and carvedilol, respectively.  In patients with relatively high (≥16%) PVC burden, "Poor" response was observed in 86.9% and 76% of patients treated with MetS and carvedilol, respectively.  Side-effects and/or intolerance were observed in 5.5 % and 13.9 % of patients treated with MetS and carvedilol, respectively.

MetS and carvedilol for idiopathic, frequent, monomorphic PVCs is frequently inefficient.  Therapeutic efficacy decreases further in patients with relatively high (≥16%) PVC burden.  "Pro-arrhythmic" response was observed in approximately one quarter of the patients.