Effects of Intraventricular Conduction Delay on Survival in Patients Taking Antiarrhythmic Drugs

An intraventricular conduction delay (IVCD) may influence the efficacy and safety of antiarrhythmic (AA) drugs. The Cardiac Arrhythmi Suppression Trial (CAST) allows assessment of the influence of an IVCD on survival when A drugs are used following myocardial infarction (MI). In CAST, MI patients with frequent ventricular premature depolarization (VPDs) (averaging 28 VPD/H) were randomized to receive an A drug (flecainide, encainide or moricizine) or placebo. After therapy was started 956 patients (35%) had an IVCD (QRS ≥ 0.11 sec) and 1796 patients (65%) had QRS < 0.11 sec. Patients IVCD patients differed from those with normal conduction by: being older (72% > age 60 vs. 54%); more often having an ejection fraction <0.30 (30% vs. 21%); more often having >50 VPD/H at baseline (51% vs. 43%); and having more pre-CAST MIs (45% vs. 38%) (P < 0.001 for each). Mean follow-up was 1.1 years. Results After adjusting for age, ejection fraction and prior MI, the combination of IVCD and antiarrhythmic drug remains significant predictor of increased mortality (hazard ratio 1.69, P = 0.04). Conclusion Antiarrhythmic drug use is associated with and possibly cause of increased mortality and arrhythmic deaths in patients with an IVCD.