Factors affecting the clinical response to treatment with digoxin and two calcium antagonists in patients with atrial fibrillation.

It has been suggested that patients in whom atrial fibrillation (AF) is associated with poor exercise tolerance respond better to treatment with xamoterol plus digoxin than to digoxin alone; this may be attributable to better control of exercise induced tachycardia. We have examined data obtained during studies comparing digoxin and two calcium antagonists in the treatment of AF to see whether subgroups of patients with particularly poor exercise tolerance, rheumatic heart disease or rapid post-exercise heart rates might derive particular benefit from one modality of treatment as opposed to another. The results do not indicate that calcium antagonists improve exercise tolerance compared with digoxin in any of these subgroups despite achieving consistently better control of exercise induced tachycardia.