Myocardial micronecrosis produced by microsphere embolization. Role of an α-adrenergic tonic influence on the coronary microcirculation

Abstract

Microspheres approximately 25 or 50 μm in diameter were systematically embolized from the left ventricular cavity. The number of microspheres given was empirically chosen to minimize the possibility of more than one microsphere lodging in an arteriole (3 mg/kg), yet was sufficient to allow for adequate histological assessment. The dogs were sacrificed after 24 hours, and focal areas of myocytolytic necrosis were noted in the myocardium. Groups of dogs were given pretreatment with drugs 10 minutes before embolization. Dogs pretreated with phentolamine (n = 8) and prazosin (n = 2) did not reveal any areas of myocardial necrosis after embolization with 25-μm microspheres. Cardiac lesions were also prevented in four of five dogs pretreated with verapamil. In contrast, cardiac lesions were not prevented by pretreatment with yohimbine (n = 2), dipyridamole (n = 3), propranolol (n = 2), or atropine (n = 2). Drug pretreatment with phentolamine or verapamil was not able to prevent cardiac lesions after embolization with 50-μm microspheres. Furthermore, despite a greater number of microspheres physically present in the subendocardial layer, the necrotic lesions were more frequent in the mid-wall and epicardial layers. Lesions produced by 25- or 50-μm emboli were also significantly smaller in the endocardium. Systemic embolization with microspheres excluding the coronary circulation did not produce cardiac lesions. We conclude that mechanical interruption of the coronary circulation with a 25-μm microsphere may be a necessary but not sufficient condition to produce cardiac necrosis. An α1-adrenergic mechanism is also involved in the production of these lesions. The distinct transmural differences in distribution and size of the embolic lesions suggest the possibilities of a nonuniform transmural α-adrenergic tonic influence on the coronary microcirculation and/or a nonuniform transmural arteriolar hierarchy within the left ventricular myocardium.