The effect of coronary artery occlusion on the cardiovascular response to an aversive stress.

Abstract

The cardiovascular response to a controlled aversive stress was investigated both before and during acute myocardial ischemia. Classical aversive conditioning (a 30-s tone reinforced with a 1-s shock) served as the model of stress while anterior wall myocardial ischemia was induced by the occlusion (hydraulic occluder) of the left anterior descending coronary artery. The conditional response consisted of significant increases (P less than 0.01) in mean arterial pressure (AP, 13.8 +/- 1.9 mm Hg, 14.3%), left ventricular (LV) dP/dtmax (1300 +/- 324 mm Hg/s, 34.7%) and heart rate (HR, 44 +/- 4 beats/min, 46.8%). Mean coronary vascular resistance significantly (P less than 0.01) increased first (CVR, 0.52 +/- 0.18 mm Hg/ml/min, 17.2%), then decreased (0.77 +/- 0.14 mm Hg/ml/min, 25.5%). In contrast, during acute myocardial ischemia both the HR and d(LVP)/dtmax conditional response were significantly reduced (P less than 0.01) by 58 and 54%, respectively (HR, 20.7 +/- 3.8 beats/min, d(LVP)/dt, 756 +/- 226 mm Hg/s). In addition, the initial CVR increase was virtually eliminated (0.13 +/- 0.10 mm Hg/ml/min, 74.0% reduction) while the CVR decrease was significantly reduced (P less than 0.01) by 48% (0.40 +/- 0.15 mm Hg/ml/min) during the coronary occlusion. The mean AP response, however, was not affected by myocardial ischemia. The pre-conditional stimulus cardiovascular variables were similarly unaffected by the coronary artery occlusion. Thus, coronary artery occlusion attenuated both the coronary and cardiac response elicited by an aversive stress. The mechanism mediating this inhibition of the conditional response remains to be determined but may involve the activation of vagal depressor reflexes during the acute ischemia.