Effect of chronic myocardial infarction on vagal cardiopulmonary baroreflex.

Sensory endings in the left ventricle are damaged by acute myocardial infarction. The goal of our experiments was to determine whether reflexes that originate in the heart are impaired by chronic myocardial infarction. Inferoposterior (n = 11) or anterior (n = 10) infarction was produced in dogs by ligation and intracoronary injection of rapidly hardening latex into either the proximal left anterior descending or left circumflex coronary arteries. Four weeks after infarction, the changes in renal sympathetic nerve activity induced by phenylephrine infusion, hemorrhage, and volume expansion were assessed before and after sinoaortic baroreceptor denervation. The results in infarct dogs were compared with the results in 11 sham-operated dogs. With arterial baroreceptors intact, baroreflex sensitivity (defined as the percent change in renal nerve activity per millimeter of mercury change in mean pulmonary artery wedge pressure) was similar in all groups of dogs. Following sinoaortic denervation, dogs with anterior and inferoposterior infarction had impaired responses to volume expansion. The responses during hemorrhage were abolished in dogs with inferoposterior infarction. We conclude that chronic myocardial infarction impairs reflexes that originate in the heart in response to changes in cardiac filling pressures.