Cardiac Preload and Afterload and the Treatment of Heart Failure, June 23, 1986

Cardiac Preload and Afterload and the Treatment of Heart Failure, June 23, 1986

1. The concept of cardiac preload and afterload

Cardiac preload refers to the end-diastolic volume of the left ventricle. The larger this volume, the stronger the heart’s contractile force and the greater the stroke volume. The end-diastolic volume of the left ventricle is directly related to the left atrial pressure, which in turn is related to pulmonary arterial pressure; therefore, clinical practice often uses pulmonary arterial pressure to represent the end-diastolic volume of the ventricle. For healthy individuals, the end-diastolic volume of the left ventricle is 120–130 mL, the end-diastolic pressure is 12 mmHg, and the pulmonary arterial pressure is 5 mmHg. Afterload refers to the resistance that prevents the left ventricle from ejecting blood; thus, peripheral vascular resistance, aortic pressure, and aortic impedance can all serve as indicators for measuring left ventricular afterload. Under physiological conditions, the left ventricular preload remains constant, while the afterload gradually increases with each heartbeat, causing the stroke volume to decrease. Normally, the heart’s preload and afterload are in dynamic equilibrium.

2. Changes in preload and afterload during heart failure

Heart failure refers to a situation where the heart’s output cannot meet the body’s needs, at which point both the left ventricular preload and afterload change. Specifically, preload increases, afterload increases, and the increase in preload is due to the enlarged end-diastolic volume of the ventricle (accumulating blood that was not previously ejected), while the increase in afterload is due to reflexive vasoconstriction throughout the body to improve systemic blood supply, effectively increasing the heart’s afterload.

3. Principles of treating heart failure

The goal is to reduce both preload and afterload through positive inotropic and negative chronotropic effects. Therefore, the purpose of treating heart failure is to lower both preload and afterload.