Comparative analysis of anti-arrhythmic effect of propranolol and metoprolol in patients with supraventricular tachyarrhythmias.

Eighty-seven patients with paroxysmal tachydysrhythmias were submitted to clinical and laboratory evaluation and electrophysiologic studies were performed during the 3rd, 6th and 12th months of the therapy with propranolol or metoprolol. Metoprolol did not induce any significant change in sinoatrial correct time, in sinoatrial recovery time or in corrected sinoatrial recovery time. It decreases significantly the effective and functional AV refractory periods as well as increases the effective refractory period of the additional pathway. The mechanism of tachycardia preventing an involvement of the additional pathway in retrograde direction consists in the appearance of a block in the indicated additional pathway. The results of the humoral aspects are the following: propranolol inhibits the functions of the thyroid and sexual glands both in acute tests and in tests performed during the 3rd, 6th and 12th month of therapy; metoprolol has no significant effect on the functions of the thyroid and sexual glands; apparently, it influences the cardiac conduction system and myocardium directly.