Natural History of Cardiac Arrhythmias and their Prevention with Quinidine in Patients with Acute Coronary Insufficiency

Abstract

In a prospective controlled clinical trial the natural history of cardiac arrhythmias and their prevention with prophylactic quinidine therapy were studied in 23 patients with acute coronary insufficiency without myocardial infarction. After a loading procedure, 300 mg of quinidine sulfate or placebo was administered orally every 6 hours for up to 5 days under balanced, random, double-blind conditions. An automated arrhythmia detection system was used to quantify arrhythmias from stored continuous electrocardiographic tape recordings. The frequency of ventricular and supraventricular arrhythmias tended to increase progressively on each successive day of study in placebo-treated patients. By contrast, in quinidine-treated patients all arrhythmias were quantitatively lower on each day of therapy and did not show a tendency toward progressive daily increases. In the placebo group there was an average of 140 premature ventricular contractions (PVC's) per day on the first day which increased to 600 PVC's per day by the fifth day, whereas with quinidine there was an average of 40 PVC's per day or less throughout the 5 days of study ( P < 0.01). The daily increase in ventricular arrhythmias in placebo-treated patients with acute coronary insufficiency during the 5 days is in contrast to the natural history of patients with documented myocardial infarction who have a marked daily decrease in the frequency of ventricular arrhythmias during the first 5 days. Significant arrhythmia suppression with quinidine was present when mean blood quinidine concentration reached a steady state above 4 mg/liter at the end of the first day of therapy. Adverse reactions to quinidine were not observed. On the basis of these data, quinidine sulfate given prophylactically at a dosage producing modest blood concentrations appeared to be both effective and safe for the prevention of ventricular and supraventricular arrhythmias that occurred during the first 5 days after an episode of acute coronary insufficiency without infarction.