Decreased contractility after myocardial hypertrophy: Cardiac failure or successful adaptation?

It is argued that in humans, as in animals! some depression of contractility in the hypertrophied myocardium may be adaptational, i.e., “normal” or physiologic, not a sign of dysfunction and not the beginning of clinical heart failure.

Abstract

A striking contradiction appears to exist between descriptions of the anirnal and human myocardial response to a chronic overload. In animals exposed to a mild to moderate pressure or volume overload, a stage can be identified where hypertrophy causes an initial depression of velocity-related indexes of contractility before maximal isometric tension development decreases or congestive h.eart failure occurs.1-7 In the rat, the observed decreased1 velocity of contraction is related to a change in myosin isozyme composition rather than to dysfunction of an unchanged contractile protein apparatus.1-4 The delcreased velocity of contraction appears to be beneficial, adaptational and physiologic, because mechanical-metabolic efficiency is improved.5s In contrast, an observed decrease in contractility in clinical studies of hypertrophy in humans has generally been interpreted as indicating myocardial dysfunction, and is usually thought to be a harbinger of the clinical heart failure that occurs as the final chapter in the natural history of cardiac overload.9 Two recent reviews of hypertrophy have defined “pathologic” hypertrophy by the presence of decreased indexes of contractile function.gJO The purposes of this paper are (1) to argue that in humans, as in animals! some depression of contractility in the hypertrophied myocardium may be adaptational, i.e., “normal” or physi.ologic, not a sign of dysfunction and not the beginning of clinical heart failure; and (2) to suggest future studies to resolve the current apparent contradiction that im:plies that a decrease in contractility after cardiac overload can be physiologic in animals, but is pathologi8c and a sign of myocardial deterioration in humans. Resolution of this issue is important not only to increase the basic understanding of the hypertrophy process, but also because a decrease in contractile function with a volume or pressure over-