Analysis of relaxation in the evaluation of ventricular function of the heart

Abstract

T HE MANAGEMENT of cardiac diseases has evolved from one of expectant observation to current medical and surgical interventions aimed at preserving or restoring myocardial function. This has led to a search for thorough understanding and evaluation of global and regional left ventricular function during systole and diastole. In the past, major research emphasis had been placed on the analysis of the contraction phase of systole. Only recently, our attention has been drawn also to the relaxation phase of systole and to diastole. In this respect, early detection of impaired relaxation has been emphasized for the evaluation of both global and regional ventricular function in patients with heart disease. Although early relaxation abnormalities have been found in various cardiac diseases that eventually lead to cardiac failure, such as hypertrophic and ischemic cardiomyopathy, the underlying mechanisms are as yet not fully understood.’ Given the recent progress in our understanding of the physiology and pathophysiology of the relaxation phase of systole of the heart as a muscle and pump,* these mechanisms can now be more easily appreciated. In this review, we will first summarize our present knowledge of relaxation of cardiac muscle. More specifically, we will describe how relaxation is controlled by three interacting determinants: (1) load, (2) (in)activation, and (3) nonuniform distribution of load and (in)activation in space and in time, and how this triple control constitutes a logical extension of a similar triple control of performance during contraction (Fig 1). Second, we will examine how this triple control applies to the intact in situ heart as a pump. Third, we will discuss how various factors, acting either alone or in concert, underlie relaxation abnormalities that occur early on in heart disease. Finally, we will critically review various measurements and indices of ventricular relaxation in view of these new concepts.