Assessment of single beat end-systolic elastance methods for quantifying ventricular contractility

Multi-beat end-systolic elastance (E_MB) is considered a gold-standard index of ventricular contractility. However, it is difficult to measure clinically due to the need for transient manipulation of ventricular preload or afterload. We compared the performance of 5 'single-beat' methods that do not require loading interventions, for estimating the equivalent of E_MB. In 7 sheep instrumented with a micromanometer/conductance catheter, single-beat methods were compared with E_MB, obtained after transiently decreasing preload or increasing afterload under a broad range of heart rates and inotropic conditions. The single-beat elastance (E_SB) method described by Shishido et al. (Circulation 102(16):1983-1989, 2000) had the highest correlation (R = 0.69, y = 0.52x + 0.43) with E_MB, although the absolute accuracy was poor. Interestingly, for all methods tested, a higher correlation was observed when E_MB was obtained with an afterload increase (R = 0.47 - 0.78) rather than a preload reduction (R = 0.07-0.57). Within-animal regression coefficients were higher than those obtained from pooled data, with excellent within-animal correlation observed for Shishido et al. method (0.73 ≤ R ≤ 0.96) when using afterload increase as the loading intervention. We conclude that (1) current methods perform better when using an afterload increase to obtain reference E_MB, (2) intra-individual E_SB comparisons may be more reliable than inter-individual comparisons and (3) Shishido et al.'s method demonstrated the strongest correlation with E_MB. Current E_SB methods have limited and variable accuracy, but may hold promise for tracking relative changes in ventricular contractility in individuals.