A reply

Abstract

We thank Drs Poelaert and Roosens for their comments regarding our manuscript. We believe a number of their points require further comment. Despite the limitations presented in our manuscript and by other investigators regarding dP/dt max, it remains a commonly used descriptor of systolic function [1, 2]. Whilst we agree that other load-insensitive indices of systolic function, such as the dP/dt max corrected for end diastolic volume (EDV) and the slope of the end systolic pressure volume relationship (ESPVR) provide information regarding myocardial contractility, we have found that in practice the slope of the preload recruitable stroke work relationship [3] remains the most robust, as it is independent of calibration – the major limiting method in PV loop construction due to the multiplicative nature of the Baan formulae [4]. Feneley and co-workers demonstrated that stroke work falls to a greater degree than does end-systolic pressure during preload reduction [5], thus providing a greater amount of information with which to extrapolate the slope of the stroke work against end-diastolic volume, with improved accuracy of slope estimation when compared with other load-independent indices of contractility. Mirsky et al. recently discussed the importance of both the slope and the intercept in the interpretation of contractility [6]. The problem of negative intercepts remains a major caveat in the interpretation of these indices. We have analysed our data on dP/dt max/EDV and compared it with ESPVR. There was no difference between measurements over the loading interventions (p = 0.806, RM-anova between subject analysis with Greenhouse-Geisser correction), indicating that dP/dt max/EDV is a load-insensitive measurement of contractility. With regard to the study by Amà et al. [7], we are concerned that the degree of change in the peak tissue Doppler systolic velocity (Sm) observed with volume loading, though statistically significant, was small (12%) and may be explained by the Frank-Starling mechanism. Unfortunately, the change in Sm was not referenced against PV loop measurements of contractility and it cannot be discounted that the increase in Sm may have been a real effect of increased contractility.