Cardiac function and myocardial contractility: A perspective

Abstract

Improved understanding of cardiac muscle and whole heart function has substantially benefited clinical diagnosis and therapy. Knowledge of the influence of systolic loading conditions has been of key importance in these advances, and the role of peripheral circulatory responses is beginning to be appreciated. Dissociations between myocardial contractility and cardiac function are described, including acute heart failure due to afterload mismatch associated with normal myocardial contractility, and normal ventricular function associated with depressed contractility in chronic mitral regurgitation. Frameworks for assessing cardiac and myocardial function are examined. Standard invasive and noninvasive approaches can now be usefully supplemented by end-systolic pressure-volume and end-systolic wall stress-volume frameworks, the former being particularly useful for analyzing the concept of "afterload mismatch with limited preload reserve" and the latter being useful for studying chronic cardiac adaptations. The clinical importance of systolic loading conditions and venous return is illustrated within these frameworks by a description of responses to a vasopressor stress test to produce an apparent descending limb of left ventricular function, the concept of steady state afterload mismatch in chronic and acute heart failure and the responses to vasodilator therapy in the normal and failing heart. The importance of changes in venous return in determining the cardiac output response to a vasodilator, in addition to the effects of reduced afterload on the ventricles, is emphasized. Finally, the problem of assessing left ventricular function in patients with chronic mitral regurgitation is examined and, for the patient with severe mitral regurgitation and few symptoms, tentative guidelines for recommending operation to avoid irreversible left ventricular dysfunction postoperatively are presented.