Evaluation of echocardiographic indices of systolic function

We read with interest the article from Royse et al. concerning the echocardiographic evaluation of systolic function [1]. In a comparative study between invasively obtained pressure-volume loops and various echocardiographically assessed variables in patients undergoing CABG, they concluded that fractional area change, afterload-corrected fractional area change and peak systolic myocardial velocity at the level of the lateral part of the mitral annulus are equivalent in assessing systolic function when compared with preload recruitable stroke work. We agree completely with the authors when they consider dP/dt max as both a preload and afterload-dependent descriptor of left ventricular systolic function, as previously described [2, 3]. However, the correction of this parameter by the end-diastolic volume has been demonstrated to behave in the same manner as the end-systolic pressure volume relationship [3]. We wonder whether Royse et al. observed the intra-operative behaviour of this variable. Knowledge of the behaviour of (dP/dt) max/end-diastolic volume would provide information on contractility, rather than a load-dependent variable such as left ventricular systolic function. This parameter could be obtained by routine echocardiography, provided mitral regurgitation is present. A similar problem may arise when using the systolic myocardial velocity at the level of the mitral annulus as a measure of systolic function. Our group recently demonstrated that this variable is load-dependent [4]. The authors claim a minimal load-dependency of this variable, which seems to be in contradiction with earlier findings. The systolic myocardial velocity taken at the level of the mitral annulus is a descriptor of systolic function rather than of contractility [5]. Echocardiographic parameters must be utilised with caution in view of load-dependency [6], which is nearly always present in critically ill patients, both in the ICU and during major surgery.