EFFECT OF PREOCCLUSION STENOSIS SEVERITY ON HEART-RATE REACTIONS TO CORONARY-OCCLUSION

Autonomic mechanisms may have an important role in the clinical presen tation of acute coronary occlusion. This research was designed to eval uate the effect of preocclusion stenosis severity on the immediate aut onomic heart rate (Ha) responses to a subsequent acute occlusion of th e coronary artery. HR and its variability in the time and frequency do mains were analyzed in patients with mild to moderate (less than or eq ual to 85%) (group 1, n = 19) and severe (>85%) (group 2, n = 18) left anterior descending coronary artery stenosis immediately before and d uring balloon occlusion (mean 108 seconds). The ranges of nonspecific responses were determined by analyzing HR reactions in a control group (n = 13) with no ischemia during balloon inflation of a totally occlu ded coronary artery. An abnormal increase in HR variability and/or bra dycardia as a sign of vagal activation occurred in 6 patients (32%) in group 1 and in 3 patients (17%) in group 2. A significant decrease in HR variability or tachycardia, or both, was observed in 5 patients (2 6%) in group 1, but in none of the patients in group 2. Compared with the control group, the balloon occlusion of mild to moderate stenosis caused abnormal HR reactions more often than did occlusion of tight st enosis (58% vs 17%, p <0.05). Balloon occlusions in group 1 caused che st pain (p <0.01), ST-segment changes (p <0.001), and narrowing of pul se pressure (p <0.05) more often than did occlusions of severe stenose s. Severe chest pain also resulted more often (p <0.01) in a premature deflation of the balloon in group 1. Thus, patients with mild coronar y stenosis often develop abnormal autonomic responses to a subsequent acute coronary occlusion, which may modify the clinical presentation o f the acute occlusion. On the other hand, if a severe coronary artery stenosis occludes, autonomic responses are rare, possibly due to chron ic ischemic preconditioning or better collateral development.