Effects of Propranolol and Epinephrine on the Electrophysiology of the Heart

Surface and intracellular electrograms and ventricular pressures were used to study the effects of epinephrine and propranolol on electrophysiological properties in the in situ heart of 21 anesthetized dogs. Five sec. after the infusion of epinephrine, the ST segment became slightly depressed. About 10 to 20sec. after epinephrine, the ST segment became elevated and the negative T wave became more inverted. Initially, the upward convexity of phase III of the membrane action potential deepened slightly. Phase II of the membrane action potential gradually decreased in amplitude and became prolonged in duration. Phase III of the membrane action potential increased slightly. The membrane resting potential remained almost unchanged. Intracellular electrographic changes due to epinephrine were of abnormal configuration. That epinephrine may cause anginal pain is well known. Propranolol inhibits epinephrine's effects on the electrophysiologic properties of the heart. It is thought that propranolol helps to relieve the pain of angina pectoris by decreasing cardiac work and by increasing coronary blood flow.