A Basic Look at Ventricular Function and Cardiac Mechanics

Abstract

During the contraction phase of the myocardium the cardiac muscle reaches its maximum state of activation near end-systole at point (P_m, V_m) on the PV-loop. The tangent to the PV-loop at (P_m, V_m) is known as the end-systolic pressure-volume relation (ESPVR). An important feature of this study is the introduction of the active pressure generated by the myocardium in the mathematical formalism describing the ESPVR (also known as the isovolumic pressure P_iso by physiologists). This mathematical formalism is used with the aim of deriving useful relations between the ejection fraction (EF), the parameters describing the ESPVR, and the areas under the ESPVR. These relations give new insight in the mechanics of ventricular contraction, it is shown that the EF is just one of several indexes that can be used in order to quantify and describe the ventricular function. Also bivariate (or multivariate) analysis of data appears to be superior to univariate analysis of data in order to assess the state of the myocardium. Criteria to study the problem of heart failure with preserved ejection fraction (HFpEF) are derived and discussed. Attention is also given to the way the ventricular geometry affects the calculation of the EF. Applications to clinical data are presented that show the consistency of the mathematical formalism used.