Pressure-volume-based single-beat estimations cannot predict left ventricular contractility in vivo

Abstract

The end-systolic pressure-volume relationship is regarded as a useful index for assessing the contractile state of the heart. However, the need for preload alterations has been a serious limitation to its clinical applications, and there have been numerous attempts to develop a method for calculating contractility based on one single pressure-volume loop. We have evaluated four of these methods. Pressure-volume data were obtained by combined pressure and conductance catheters in 37 pigs. All four methods were applied to 88 steady-state pressure-volume files, including eight files sampled during dopamine infusions. Estimates of single-beat contractility (elastance) were compared with preload-varied multiple-beat elastance [ E es(MB)]. All methods had a low average bias (−0.3 to 0.5 mmHg/ml) but limits of agreement (±2 SD) were unacceptably high (±2.6 to ±3.8 mmHg/ml). In the dopamine group, E es(MB) showed an increase of 1.7 ± 0.8 mmHg/ml (mean ± SD) compared with baseline ( P < 0.001). None of the single-beat methods predicted this increase in contractility. It is therefore doubtful whether any of the methods allow for single-beat assessment of contractility.