Assessment of afterload

Abstract

Afterload can be thought of as the tension acting on the fibers in the ventricular wall during ejection or as the impedance to ejection.¹ Although it is influenced importantly by the arterial pressure, it is not synonymous with peripheral arterial pressure, peripheral vascular tone, or systemic vascular resistance. Afterload is best defined as left ventricular wall stress during ejection according to La Place’s law:²

$${\text{Wall stress = PR/2h,}}$$

(1)

where P is the intracavitary pressure, R is the radius of curvature, and h is the wall thickness. Thus, wall stress is directly related to chamber dimension, and inversely related to wall thickness. While arterial pressure is related to the product cardiac output and systemic vascular resistance, afterload (wall stress) is a function of ventricular size and arterial pressure. Fig. 5.1. illustrates the great difference between wall stress, i.e., afterload, and systolic ventricular pressure.