Myocardial viability

Abstract

When facing dangerous environmental situations, most animal species react with a sympathoadrenergic fight or flight activation; others, such as the opossum, react with a vagal sympatho-inhibitory discharge or the play dead reaction, which discourages possible predators. The myocardium reacts to dangerous situations with opossum-like behavior. In several altered myocardial states (ischemia, hibernation, stunning), when the local supply–demand balance of the cell is critically endangered, the cell minimizes expenditure of energy used for development of contractile force, accounting at rest for about 60 % of the high-energy phosphates produced by cell metabolism, and utilizes whatever is left for the maintenance of cellular integrity. The echocardiographic counterpart of this cellular strategy is the regional asynergy of viable segments [1]. Both viable and necrotic segments show a depressed resting function [2], but the segmental dysfunction of viable regions can be transiently improved or even normalized by proper inotropic stimulus. From the pathophysiological and experimental viewpoint, stunning and hibernation are sharply separated entities (Table 20.1). Between fully reversible ischemia and ischemia lasting more than 15–20 min, invariably associated with necrotic phenomena, there is a blurred transition zone. Within this gray zone, ischemia is too short to cause myocardial necrosis but long enough to induce myocardial stunning: a persistent contractile dysfunction lasting for hours, days, and even weeks after the restoration of flow [1].