EFFECT OF DEXTRO ISOMER OF PROPRANOLOL ON SINUS RATE AND CARDIAC ARRHYTHMIAS

Previous workers have shown experimentally that dl-propranolol, in addition to its β-blocking action, has a direct depressant effect on cardiac muscle and terminates arrhythmias due to digitalis overdosage. The dextro isomer of propranolol has very little β-blocking activity compared with dl-propranolol, but has an equivalent direct myocardial action. In this investigation d-propranolol, and in most cases dl-propranolol also, was given to 25 patients in sinus rhythm and 59 with cardiac arrhythmias. d-Propranolol had much less effect than dl-propranolol on sinus rate and on ventricular rate in atrial flutter and fibrillation. In supraventricular and ventricular ectopic beats and tachycardias, however, either both drugs were ineffective or they had approximately equivalent effects. d-Propranolol terminated digitalis arrhythmias. It is suggested from these observations that the actions of dl-propranolol on the sinus node and on the atrioventricular node in atrial flutter and fibrillation are through β blockade. In other ectopic arrhythmias and in digitalis intoxication, its action is by a mechanism or mechanisms other than β blockade. © 1968.