Cardiac parasympathetic efferent activities during myocardial ischemia

Efferent parasympathetic neural activities from two cardiac nerves were simultaneously recorded in 33 dogs. Efferent innervation patterns were determined using heart rate, atrioventricular conduction, and regional force responses to electrical stimulation. Intravenous hexamethonium was administered to eliminate postganglionic activity. Baroreflex challenge verified efferent neural responsiveness. Recordings were made in 22 nerves in 11 sham-operated dogs. Left ventricular ischemia was produced by a 30-minute occlusion of a branch of the left circumflex or left anterior descending coronary arteries. Heart rate and mean arterial blood pressure did not significantly change during myocardial ischemia. Of the 52 nerves recorded during myocardial ischemia, 24 innervated ischemic regions and 28 innervated nonischemic regions. Parasympathetic activities to both the ischemic and nonischemic cardiac regions exhibited significant decreases during left circumflex or left anterior descending coronary artery occlusions of 30 minutesʼ duration. Recordings in sham-operated animals exhibited no significant changes in neural activities over time. Bilateral stellectomy (sympathetic deafferentation), bilateral thoracic vagotomy (vagal deafferentation), or phenol painting of the epicardium of the left ventricle (deafferentation of the ischemic region) abolished the efferent parasympathetic depression caused by coronary artery occlusion. Thus, in contrast to differential changes in sympathetic efferent activities, there is a generalized decrease in efferent parasympathetic activity during 30 minutes of acute myocardial ischemia that is mediated through afferent signals from the heart that course in both the vagi and sympathetic nerves.