Differential cardiac sympathetic activity during acute myocardial ischemia

Efferent sympathetic activities were simultaneously recorded from two thoracic cardiac nerves in 33 chloralose-anesthetized dogs. Efferent innervation patterns were determined by electrical stimulation prior to recording in each animal. One of the nerves selected for recording was shown to innervate the proposed ischemic region, whereas the other nerve was selected because it was shown to innervate nonischemic regions. Left ventricular ischemia was produced by occlusion of a branch of either the left anterior descending (LAD) or left circumflex (LCX) coronary arteries. Heart rate was paced. Cardiac postganglionic sympathetic efferent activities were recorded during a 30-min coronary occlusion in 22 animals. Thirty minutes after LAD occlusion (n = 10), postganglionic sympathetic activity to ischemic myocardium was decreased (84 +/- 5% of control; P less than 0.05) while activity to nonischemic myocardium was unchanged. Thirty minutes after LCX occlusion (n = 12), postganglionic sympathetic activity to ischemic myocardium was also decreased (87 +/- 3% of control; P less than 0.01); however, sympathetic activity to nonischemic myocardium was increased (159 +/- 10% of control; P less than 0.001). Thus, in the anesthetized canine, regional left ventricular ischemia elicits differential sympathetic neural responses that are dependent on the location of the ischemic myocardium as well as the efferent destinations of the nerves. Changes in cardiac postganglionic sympathetic efferent activities are characterized by decreased activity to ischemic regions, with either no change or increased activity to nonischemic regions.