Validation of noninvasive indices of global systolic function in patients with normal and abnormal loading conditions: a simultaneous echocardiography pressure-volume catheterization study

Abstract

Background: Noninvasive indices based on Doppler echocardiography are increasingly used in clinical cardiovascular research to evaluate left ventricular global systolic chamber function. Our objectives were to clinically validate ultrasound-based methods of global systolic chamber function to account for differences between patients in conditions of abnormal load, and to assess their sensitivity to load confounders.

Methods and results: Twenty-seven patients (8 dilated cardiomyopathy, 10 normal ejection fraction, and 9 end-stage liver disease) underwent simultaneous echocardiography and left heart catheterization with pressure-conductance instrumentation. The reference index, maximal elastance (Emax), was calculated from pressure-volume loop data obtained during acute inferior vena cava occlusion. A wide range of values were observed for left ventricular systolic chamber function (Emax: 2.8±1.0 mm Hg/mL), preload, and afterload. Among the noninvasive indices tested, the peak ejection intraventricular pressure difference showed the best correlation with Emax (R=0.75). A significant but weaker correlation with Emax was observed for ejection fraction (R=0.41), midwall fractional shortening (R=0.51), global circumferential strain (R=-0.53), and strain rate (R=-0.46). Longitudinal strain and strain rate failed to correlate with Emax, as did noninvasive single-beat estimations of this index. Principal component and multiple regression analyses demonstrated that peak ejection intraventricular pressure difference was less sensitive to load, whereas ejection fraction and longitudinal strain and strain rate were heavily influenced by afterload.

Conclusions: Current ultrasound methods have limited accuracy to characterize global left ventricular systolic chamber function in a given patient. The Doppler-derived peak ejection intraventricular pressure difference should be preferred for this purpose because it best correlates with the reference index and is more robust in conditions of abnormal load.

Keywords: cardiac catheterization; echocardiography; hemodynamics; systole.

Figure 1

Examples of invasive and echocardiographic indices of LV systolic function in representative patients with chest pain and normal EF (left), dilated cardiomyopathy (center) and liver cirrhosis (right). Panel A. Pressure-volume loops obtained during inferior vena cava occlusion. Maximal elastance (E_max) is obtained as the slope of the ESPVR. Panel B. Circumferential (blue) and longitudinal (red) global strain and strain rate tracings obtained from 2-dimensional echocardiographic images using speckle-tracking software; the peak global strain and strain rate are depicted (*). Panel C. Intraventricular pressure gradient maps obtained by post-processing color Doppler M-mode images (upper row) and pressure difference waveforms between the apex and the outflow tract (lower row). The peak ejection intraventricular pressure difference (peak-EIVPD) is depicted in each curve (•).

Figure 2

Scatterplot, linear fitting (dotted line) and 95% confidence interval for the fitting (grey ribbon) of Doppler-derived ejection intraventricular pressure difference (Peak-EIVPD) versus left ventricular maximal elastance (E_max).

Figure 3

Principal components analysis with illustrative variables. The autocorrelation of the noninvasive indices of systolic function (black circles) and their relationship with LV maximal elastance (E_max), mass, preload and afterload (red circles) is represented using a correlation circle. Axes represent the first (horizontal) and second (vertical) principal components (% of variation explained by each). The angle between two arrows represents the correlation between the respective variables. There is a positive correlation if the angle is small (variables are close to each other), there is no linear correlation if the angle is 90°, and there is an inverse correlation if the angle is > 90°. The closer a variable is to the boundary circle of correlations (arrow length closer to 1), the better it can be reconstructed from the first two components. EIVPD: Ejection intraventricular pressure difference; EF: ejection fraction; MWFS: mid-wall fractional shortening; S_circ: Circumferential strain; SR_circ: Circumferential strain rate; S_long: Longitudinal strain; SR_long: Longitudinal strain rate; E_max-sb1: Single-beat E_max estimated by method 1; E_max-sb2: Single-beat E_max estimated by method 2 (see text for details).