ABSTRACT. The effects of physical exercise, isoproterenol and atropine upon the ventricular rate and regularity were studied in 12 patients with atrial fibrillation (AF) during verapamil‐induced regular ventricular rhythm. Physical exercise, isoproterenol and atropine all caused a gradual loss of ventricular regularity during AF. Verapamil caused a reduction of exercise heart rate during AF and, to a minor extent, even during sinus rhythm. The regular ventricular rhythm induced by verapamil during AF is interpreted as a total AV‐nodal block with nodal escape rhythm. Possible clinical benefits of this rhythm are discussed.

Summary: Adequate control of ventricular rate in patients with chronic atrial fibrillation (AF) may not be achieved with digitalis alone. In the present study the additional effect of two different doses (50 mg and 50 + 50 mg) of oral metoprolol, a new selective p-blocking agent, on ventricular rate in patients with longstanding AF has been studied. A decrease in the mean ventricular rate during rest and during exercise at various work loads was observed after both doses. The effect was more pronounced at the highest work load of 80 W, both after 50 mg (p < 0.002) and after 50 + 50 mg (p < 0.01) of the drug. A high initial heart rate at rest or during exercise was reduced more by the drug than a lower one. Exercise tolerance was reduced in 2 patients. These results suggest that patients with AF in whom satisfactory control of heart rate cannot be achieved with digitalis alone may benefit from addition of individualized metoprolol therapy. Keywords: atrial fibrillation, digitalis, metoprolol, heart rateThe various symptoms of cardiac disability in cases of atrial fibrillation are partly caused by the rapid ventricular response. When atrial fibrillation is associated with a high heart rate the classic therapeutic approach has been to The study has been supported with grants from The Swedish National Association against Heart & Cheast Diseases. administer increasing doses of digitalis to slow the ventricular rate to an acceptable level by its blocking effect at the atrioventricular (AV) node. "Therapeutic" plasma levels of digitalis are in many instances insufficient to evoke an adequate AV blocking effect (6). In many cases "toxic" blood levels of digitalis may be required and quite often even these are inadequate to control the ventricular rate (5,6).Patients in atrial fibrillation with an inadequate digitalis induced decrease in A V conduction may benefit from any additional drug that is able to decrease A V conduction. In this study, we have therefore attempted to evaluate the effect of different doses of metoprolol, a beta-adrenergic blocking agent (2) upon the A V conduction in patients with atrial fibrillation who were already being treated with digitalis. Patients and MethodsTen patients (7 men and 3 women) suffering from chronic atrial fibrillation were selected for the present study. Pertinent clinical details for these patients are given in Table I. The patients were between 42 and 72 years of age, with a mean age of 57.2 years. Four patients had mitral valve disease (one of whom had been operated upon for mitral stenosis), four had lone atrial fibrillation, one thyreotoxicosis and the remaining patient had hypothyroidism. All these patients were in functional group I or II according to the classification of the New York Heart Association.The duration of atrial fibrillation ranged between 2 months and 3 years. DC conversion of the atrial fibrillation had been tried in all patients but they either did not revert to sinus rhythm or relapsed rapidly into atrial fibrillation.Cardiac volume -evaluated by the ...