Systolic Versus Diastolic Dysfunction
Systolic dysfunction is characterized by a decrease in myocardial contractility. A reduction in the left ventricular ejection fraction (LVEF) results when myocardial contractility is decreased throughout the left ventricle. Cardiac output is maintained in two ways: left ventricular enlargement results in a higher stroke volume, and the Frank-Starling relationship (an increase in contractility in response to an increase in stretch). However, these compensatory mechanisms are eventually exceeded and cardiac output decreases, resulting in the physiologic manifestations of heart failure. The left heart cannot pump with enough force to push a sufficient amount of blood into the systemic circulation. This leads to fluid backing up into the lungs and pulmonary congestion. Systolic dysfunction is a characteristic of dilated cardiomyopathy (DCM). It is also seen in some patients with hypertrophic cardiomyopathy (HCM) who develop progressive left ventricular dilatation and a decrease in LVEF. In general terms, systolic dysfunction is defined as an LVEF less than 40%.
Diastolic dysfunction refers to cardiac dysfunction in which left ventricular filling is abnormal and is accompanied by elevated filling pressures. The diastolic phase of cardiac function includes two components. Left ventricular relaxation is a process that takes place during isovolemic relaxation (the period between aortic valve closure and the mitral valve opening) and then during early rapid filling of the ventricle. Later in diastole, after relaxation is complete, further left ventricular filling is a passive process that depends on the compliance, or distensibility, of the myocardium. The ventricles are unable to relax, and subsequent muscle hypertrophy occurs which then leads to inadequate filling. Diastolic dysfunction may lead to fluid accumulation, especially in the feet, ankles, and legs, and some patients may also have pulmonary congestion. For patients with heart failure but without systolic dysfunction, diastolic dysfunction is the presumed cause. Diastolic dysfunction is characteristic of both HCM and restrictive cardiomyopathy (RCM). However, some component of diastolic dysfunction is also common in patients with DCM. In general terms, diastolic dysfunction is defined as an LVEF of greater than 40%.
Diastolic dysfunction is more difficult to identify with echocardiograph scanning than systolic dysfunction, and it may be missed or underestimated in many cases. Doppler scan assessment of transmitral flow is the standard approach to detect diastolic dysfunction, although a variety of other measurements can be used. It is important to understand that some of the symptoms of systolic and diastolic heart failure are similar.
Journal for Nurse Practitioners. 2007;3(4):248-258. © 2007 Elsevier Science, Inc.
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