Beta-blocking therapy in atrial and ventricular tachyarrhythmias: experience with nadolol

The effects of nadolol (N) and propranolol (P) were studied in atrial and ventricular tachyarrhythmias. Interpretation of the results should take into account the dependence of the arrhythmia on the sympathetic tone, and the drug effect on the sinus node frequency. The day/night ratio of the sinus rate is too sensitive a marker of beta blockade to evidence a difference between the two drugs at usual dosages. In contrast, even slight differences (2 to 4 bpm/24 hr) in the absolute value of cardiac frequency may be significant in homogeneous groups of patients treated with high, moderate or low dosages of P or N and, for the latter, on a short- or long-term basis. In 22 of 23 cases of idiopathic adrenergic-dependent atrial tachycardia or fibrillation that were resistant to P (160 mg/day), N (160 mg/day) was effective on a short-term basis, whereas 11 cases of vagally induced atrial flutter-fibrillation were more aggravated by N than by P. However, after 2 weeks to 2 months, 15 of 22 adrenergic-dependent atrial tachyarrhythmias escaped from the initial control, and type I antiarrhythmic agents had to be combined with N. The absence or loss of efficacy of the beta-blocking treatment coincides with the different short-term effects of P and N on the sinus rate and with the different short-term and long-term effects of N. Better efficacy of N over P was also found at the ventricular level when two groups of adrenergic-dependent (nine patients) or nonadrenergic-dependent (10 patients) ventricular tachyarrhythmias of nonischemic origin were compared. At this level, no escape phenomenon was observed. In conclusion, the antiarrhythmic effect of beta blockers essentially depends on the mechanism of the arrhythmia itself. The changes in the sinus rate values reflect the degree of beta blockade, and the antiarrhythmic efficacy depends not only on the dosage but also on the nature of the drug used.