Cardiac Inotropic and Coronary Vascular Responses to Countershock

Abstract

These experiments were designed to examine the role of excitation of intracardiac nerves in the response to countershock with either alternating current (ac) or direct current (dc). Studies were performed on intact anesthetized dogs and on isolated perfused hearts. In intact dogs a-c and d-c countershock produced transient sinus arrest and an increase in myocardial contractile force. Sinus arrest could be prevented with atropine, and the positive inotropic response could be prevented with propranolol or prior surgical denervation of the heart. In isolated hearts, a-c and d-c countershock produced sinus arrest which could be prevented with atropine or hemicholinium-3. Alternating-, but not direct-, current countershock increased contractile force of the isolated heart. The inotropic response to ac could be blocked with propranolol and was absent in hearts removed from dogs which had undergone prior cardiac denervation. Both a-c and d-c countershock produced a decrease in coronary vascular resistance which could be prevented with atropine. Cholinergic responses to countershock persisted after surgical denervation of the heart. These observations provide evidence for excitation of intracardiac cholinergic and adrenergic nerves by countershock. Direct-current countershock excites cardiac sympathetic nerves in intact dogs, but not in isolated hearts. Intracardiac cholinergic nerves persist after surgical denervation of the heart.