To the Editor:
We would like to thank you for the opportunity to respond to the issues raised in the letter by Lim1 and to clarify aspects of our methodology in relation to these concerns. We would also like to thank Lim1 for his interest in our article and for taking the time to express his concerns.
In his letter, Lim1 explains the mathematical development, from Sunagawa et al.2, showing that left ventricular ejection fraction (LVEF) is determined by loading conditions and contractility. In fact, this is the mathematical expression of the mechanism that is graphically depicted in Figures 1 and 2 in our study.3 The interest of the concept of elastance is that both left ventricular (LV) contractility and loading conditions may be expressed in the same unit.2 Changes in contractility may be masked by changes in afterload. Indeed, either using Equation 3 in the letter by Lim1 or Figure 2 in our study, everyone can understand that LVEF may decrease while contractility increases because afterload (represented by arterial elastance, Ea) increases.3 However, volume axis intercept “V0” should not be neglected for precise assessment of LV contractility (represented by end-systolic elastance, Ees), mainly in failing heart. As repeated by Lim,1 we want to highlight that LVEF should be interpreted in the context of its determinants to avoid misleading conclusions about LV function. So, we fully agree that LVEF is not simply a measure of LV function. Indeed, LVEF is highly dependent on loading conditions (even more in failing heart), while Ees, which is derived from end-systolic pressure-volume relationship, is insensible to changes in loading conditions.2 As a result, as clearly illustrated in our case report and kindly emphasized by Lim,1 changes in LVEF may not reflect changes in contractility when loading conditions are changing.
Medical Intensive Care Unit
Department of Medicine
University Hospital of Liège
1. Lim HS. The physiologic basis of ejection fraction. Opthal Plast Reconstr Surg, 2018.
2. Sunagawa K, Maughan WL, Burkhoff D, Sagawa K. Left ventricular interaction with arterial load studied in isolated canine ventricle. Am J Physiol 1983.245(5 Pt 1): H773–H780.
3. Morimont P, Lambermont B, Guiot J, et al. Ejection fraction may not reflect contractility: Example in veno-arterial extracorporeal membrane oxygenation for heart failure. ASAIO J 2018.64: e68–e71.