Effects of Afterload and Preload on Right Ventricular Systolic Performance

Abstract

Myocardial preload may be defined as the passive stretch applied prior to the initiation of active contraction. Afterload may be defined as instantaneous myocardial stress or tension achieved during active contraction. Clinical application of the concepts of myocardial preload and afterload to the intact ventricle is more difficult for the right ventricle than for the left ventricle. For both ventricles, relative preload may be estimated by measurement of end-diastolic volume, derived by contrast ventriculography, radionuclide ventriculography, or echocardiography, although these measurements are generally less exact for the right ventricle than for the left ventricle. Afterload, or systolic wall stress, is directly related to intracavitary pressure and to internal ventricular dimension and inversely related to ventricular wall thickness. Estimates of circumferential wall stress have been widely empoyed with regard to the left ventricle, with which reasonably accurate calculations may be made using models that assume a regular ellipsoidal shape. For the right ventricle, both the complex geometry and the difficulty in estimating wall thickness make estimates of systolic stress incaccurate. Nevertheless, estimates of local right ventricular systolic stress have been mace {1–3}. Many studies have relied upon less exact, but more easily derived, measures of acute changes in afterload such as pulmonary artery or right ventricular peak-systolic or end-systolic pressure {4–8}.