Increased ventricular response rate during exercise in patients with atrial fibrillation treated with theophylline.

The effect of theophylline on atrioventricular conduction in atrial fibrillation was investigated by determining ventricular response rates at rest and during exercise treadmill tests in eight patients (mean [+/- SEM] age, 64.2 +/- 2.0 years) with chronic atrial fibrillation. Tests were performed before and after 7 days of oral theophylline treatment (plasma level, 87.7 +/- 7.8 mumol/L). There was no significant change in baseline ventricular rate or duration of exercise, but the maximum ventricular rate with theophylline treatment was 12.3% +/- 2.4% higher than that with placebo (176.3 +/- 7.5 vs 158.1 +/- 8.8 beats per minute), and, during each stage of exercise, the ventricular rate with theophylline exceeded that with placebo. The increased heart rate during theophylline administration occurred without a significant difference in the exercise-induced increase in circulating plasma catecholamine levels. We conclude that treatment with theophylline may contribute to difficulties with rate control in acutely ill patients with coexisting atrial fibrillation.