CARDIAC SYMPATHETIC EFFERENT ACTIVITIES DURING MYOCARDIAL-INFARCTION

Cardiac sympathetic efferent nerve activities were recorded during 180-minute coronary artery occlusions in 23 pentobarbital-anesthetized dogs. Atria were paced (147+/-4 bpm). During left anterior descending coronary artery occlusion, cardiac nerve activities to normal and infarcted areas significantly increased to 168%+/-22% and 170%+/-25% of control, respectively. During left circumflex coronary artery occlusion, sympathetic activities to normal myocardium were significantly depressed (90%+/-15%), whereas sympathetic activities to infarcted areas were significantly elevated (123%+/-13%). Neural activities in a group of sham dogs did not change. A modest but significant trend existed for mean arterial pressure to decline (110+/-3 to 100+/-4 mm Hg) during the experiment. Regional contractile force was significantly depressed (43%+/-7% of control) in infarcted areas and did not change in normal myocardium (111%+/-9%). The percent of the myocardium made ischemic was 21%+/-2% of the ventricular wet weight. Thus, myocardial infarction after coronary artery occlusion elicits changes in cardiac sympathetic efferent activities that depend on the location of infarcted area and the efferent fiber innervation destination. Anterior infarction caused an increase in sympathetic activities. Posterior infarction caused sympathetic activities to normal myocardium to decrease and sympathetic activities to infarcted areas to increase. These differential responses may influence arrhythmogenesis associated with myocardial infarction.