Towards improved control of atrial fibrillation.

Patients with atrial fibrillation frequently show a wide variation in heart rate with digoxin therapy. We have compared the effect on heart rate variability, of doubling the digoxin dosage or adding verapamil 120 mg daily in a randomized cross-over study in 14 patients. Twenty-four hour ambulatory electrocardiographic recordings, six minute walking tests and palpitation and breathlessness scores were obtained on each regime. All patients exhibited a diurnal pattern in heart rate variability. Both treatments significantly lowered heart rate but high dose digoxin lowered minimum heart rate significantly more than digoxin and verapamil, causing more night time bradycardia. Overall, digoxin with verapamil produced significantly less heart rate variability than digoxin alone. Day time but not night time pauses were prolonged by digoxin and verapamil but were prolonged more by high dose digoxin. Five (36%) patients had serum digoxin levels in the toxic range when taking high dose digoxin. Palpitations were significantly reduced by both treatments but most improvement occurred with digoxin and verapamil. No significant effect was found on six minute walking distances or breathlessness scores. In conclusion, the addition of verapamil to digoxin was superior to increasing the dose of digoxin alone, producing significantly better control of heart rate variability with less night time bradycardia.