Incidence of proarrhythmic effects from quinidine in the outpatient treatment of benign or potentially lethal ventricular arrhythmias.

To determine the prevalence and importance of proarrhythmic events secondary to the initiation of quinidine therapy in outpatients with benign or potentially lethal ventricular arrhythmias, the data from 360 patients treated with quinidine as part of 3 outpatient drug trials were retrospectively reviewed. These patients had at least 30 ventricular premature complexes per hour during placebo treatment and had no evidence of unstable clinical states, hypokalemia, digitalis toxicity, atrial fibrillation or a prolonged QT interval (longer than 0.50 second). The quinidine dose varied from 200 to 400 mg 4 times a day for 2 to 4 weeks. Proarrhythmic effect was defined on Holter monitoring as a 400% increase in frequency of ventricular premature complexes, the presence of new ventricular tachycardia not previously identified or a 10-fold increase in the number of beats of ventricular tachycardia. There was no difference in the demography, response to quinidine therapy or side effects on quinidine among the 3 trials. Six of 360 patients (2%) had a proarrhythmic response and none of these patients had hemodynamic symptoms, required hospitalization or died from the proarrhythmic event. Thus, quinidine can be safely initiated to outpatients who meet the inclusion criteria cited herein.