Left ventricular function and its echocardiographic assessment
Cardiac function depends on a large number of parameters, including atrial function, valvular function, and ventricular function. A large body of science has demonstrated that these parameters are highly interdependent and rather complex. Indeed, myocardial mechanics constitute a whole research field. Cardiac function is also dependent on circulatory, pulmonary, renal and neurohormonal factors. These factors, which influence cardiac function primarily by affecting ventricular function, include blood pressure, venous return, pulmonary gas exchange efficiency, the concentration of catecholamines, angiotensin, hemoglobin, etc. A vivid example of how cardiac function can be affected by targeting peripheral mechanisms is illustrated by the use of ACE inhibitors and beta-blockers in heart failure; these drugs antagonize neurohormonal mechanisms and improve cardiac function and survival dramatically in heart failure (Yancy et al).
Acquiring a basic understanding of cardiac function requires an understanding of myocardial mechanics. This section covers all clinically relevant aspects of myocardial mechanics, with emphasis on echocardiographic aspects. The bulk of the discussion concerns left ventricular function, which has been studied intensely over several decades. Left ventricular function correlates strongly with total and cardiovascular mortality (Curtis et al). Among patients with coronary heart disease, left ventricular function is actually a stronger predictor of death than the atherosclerotic burden. Assessment of the size, mass, geometry, and function of the left ventricle is fundamental for the diagnosis and prognosis of most cardiac diseases, including coronary artery disease, heart failure, arrhythmias, structural heart disease, etc.
Over the years, a large number of parameters have been introduced to assess left ventricular function. The majority of these parameters can be calculated or approximated using two-dimensional echocardiography. The most widely adopted parameter is the ejection fraction (EF). The concept of ejection fraction was introduced by Braunwald and colleagues in 1962 (Braunwald et al) and it has since then been the dominating method for assessing ventricular function. For better or worse, ejection fraction has become virtually synonymous with left ventricular function.
An obvious drawback with the use of the ejection fraction is that it only assesses systolic function. Research in recent years has demonstrated that left ventricular diastolic function is also fundamental to global cardiac function. Diastolic dysfunction results in a special type of heart failure, referred to as heart failure with preserved ejection fraction (HFPEF). HFPEF may be more common than heart failure with reduced ejection fraction (HFREF, Redfield et al).
Echocardiography is the principal modality for investigating left ventricular systolic function and diastolic function. M-mode, 2D echocardiography and Doppler are all used to examine various parameters. Three-dimensional (3D) echocardiography has become increasingly common, and may be as precise as cardiac MRI (magnetic resonance imaging) for calculating ejection fraction.
References
Redfield et al: Heart Failure with Preserved Ejection Fraction. NEJM 2016.
