Heart failure: ventricular dysfunction and Starling's Law
THE CONTEXT
Heart failure occurs when cardiac output cannot meet circulatory demands. Ventricular dysfunction and changes in the relationship between filling and performance explain its development.
Determinants of cardiac output
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Cardiac output is determined by preload, afterload and myocardial contractility.
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Preload refers to the volume and pressure of blood in the ventricles at the end of diastole.
Ventricular dysfunction
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Ventricular dysfunction is the most common cause of heart failure.
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Systolic dysfunction involves impaired contraction due to myocardial disease.
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Diastolic dysfunction involves abnormal relaxation of a stiff, non-compliant ventricle and is most commonly found in patients with left ventricular hypertrophy.
Starling relationship
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Ventricular performance is related to the degree of myocardial stretching. Increasing preload enhances function, but overstretching causes marked deterioration.
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Preload can be represented by end-diastolic volume, end-diastolic pressure, filling pressure or atrial pressure.
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In heart failure, the ventricular performance curve moves to the right and becomes flatter.
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Increased myocardial contractility or reduced afterload shifts the curve upwards and to the left.