Influence of exercise on arrhythmias induced by digitalis-diuretic therapy in patients with atrial fibrillation

Abstract

Serial low-level treadmill exercise testing was performed by 20 ambulatory patients with atrial fibrillation to provoke and study drug-related arrhythmias. All 20 were receiving long-term digitalis therapy; 19 were also receiving potassium-losing diuretic agents, and 3 had hypokalemia. The subjects were selected on the basis of resting electrocardiograms compatible with strong digitalis effects: prominent ST-T-U changes, intermittently occurring junctional beats, controlled ventricular rates (range 40 to 70/min) or ventricular premature beats. Arrhythmias suggesting digitoxicity were induced by exercise in all 20 subjects. Those occurring most often were junctional tachycardia with or without Wenckebach exit block, frequent ventricular premature beats and bigeminy. Idioventricular rhythm was induced in two subjects and ventricular parasystole in one. After withdrawal of digitalis and diuretic agents, subsequent exercise tests demonstrated increased ventricular rates, a decrease in ST-T-U changes and in the occurrence of most arrhythmias. In 18 patients, brief runs of junctional tachycardia persisted but occurred less often. Low-level exercise testing provides a simple method for provoking latent cardiac irritability in patients with suspected digitalis and diuretic toxicity; serial exercise testing after withdrawal of the drugs can demonstrate the devolution of arrhythmias.