Vasospasm of Atherosclerotic Coronary Arteries Precipitates Acute Ischemic Myocardial Damage in Myocardial Infarction-Prone Strain of the Watanabe Heritable Hyperlipidemic Rabbits

Abstract

Objective—This study tested the hypothesis that vasospasm can trigger coronary plaque injury and acute ischemic myocardial damage. Approach and Results—Myocardial infarction–prone strain of the Watanabe heritable hyperlipidemic rabbits received an intravenous bolus of ergonovine maleate (0.45 µmol/kg) during intravenous infusion of norepinephrine (12 nmol/kg per minute) to provoke coronary spasm in vivo. After this treatment, coronary angiography demonstrated vasospasm, and the ECG showed ischemic abnormalities (ST depression/elevation and T-wave inversion) in 77% of animals (23/30). These changes normalized after nitroglycerin injection. In rabbits that demonstrated these ECG findings for >20 minutes, echocardiograms showed left ventricular wall motion abnormality. Serum levels of heart-type fatty acid–binding protein, cardiac troponin-I, and myoglobin increased markedly 4 hours after spasm provocation. In coronary lesions of myocardial infarction–prone strain of the Watanabe heritable hyperlipidemic rabbits with provoked coronary spasm, we observed intimal injury in 60.9% in the form of endothelial cell protrusions (39.1%), denudation (30.4%), and macrophage extravasation (56.5%). Plaque disruption with luminal thrombus, however, was only seen in 2 of 23 animals (8.7%), and mural microthrombus was rarely observed (4.3%). Conclusions—These observations show that provocation of vasospasm in myocardial infarction–prone strain of the Watanabe heritable hyperlipidemic rabbits associates with subsequent ischemic myocardial damage. Although treatment with spasmogens altered aspects of plaque morphology, for example, endothelial protrusion and macrophage emigration, thrombosis was rare in these animals with chronic atherosclerotic disease.