Therapeutic Inefficacy and Proarrhythmic Nature of Metoprolol Succinate and Carvedilol Therapy in Patients With Idiopathic, Frequent, Monomorphic Premature Ventricular Contractions.

Background: Antiarrhythmic drugs remain the first-line therapy for treatment of idiopathic ventricular arrhythmias.

Study Question: 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 Design: Study population consisted of 114 consecutive patients: 71 received MetS and 43 received carvedilol.

Measures And Outcomes: 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 "proarrhythmic" responses (>50% increase) based on change in PVC burden compared with baseline.

Results: Most common presenting symptom was palpitations (65.8%), followed by coincidental discovery (29%). The mean MetS and carvedilol dosages were 65.57 ± 30.67 mg/d and 23.66 ± 4.26 mg/d, respectively. "Good," "poor," and "proarrhythmic" responses were observed in 11.3% and 16.3%, 63.4% and 67.4%, and 25.3% and 16.3% of patients treated with MetS and carvedilol, respectively. In patients with relatively high (≥16%) PVC burden, the sum of "poor"/"proarrhythmic" response was observed in 95.5% and 86.4% of patients treated with MetS and carvedilol, respectively. "Proarrhythmic" response was observed in 21.9% of the patients, particularly in the presence of relatively lower (≤10%) baseline PVC burden. Patients with "good" response during beta-blocker therapy had higher baseline daily average intrinsic total heart beats compared with patients with "poor"/"proarrhythmic" response combined (96,437 ± 26,488 vs. 86,635 ± 15,028, P = 0.047, respectively). Side effects and intolerance were observed in 5.6% and 18.6% of patients treated with MetS and carvedilol, respectively.

Conclusions: MetS and carvedilol for idiopathic, frequent, monomorphic PVCs are frequently inefficient. Therapeutic efficacy decreases further in patients with relatively high (≥16%) PVC burden. Relatively higher baseline daily intrinsic total heart beats may be used to predict "good" response before beta-blocker therapy.