Evaluation of ventricular-arterial coupling by impedance cardiography in healthy volunteers

The interplay between cardiac function and the arterial system is currently defined as ventricular-arterial coupling (VAC) and it is an expression of global cardiovascular efficiency. VAC involves a variety of complex interactions between the heart and the vasculature. A basic index of VAC is the ratio of effective arterial elastance (Ea)/ end-systolic elastance (Ees). While this is often done with echocardiography, obtaining Ea/Ees using impedance cardiography is feasible, although this possibility has not been explored so far.

The aim of this study was to compare the Ea/Ees values obtained using echocardiography and impedance cardiography.

Two independent operators estimated Ea/Ees in 91 (41  ±  14 years old, women 51%) untreated apparently healthy individuals using (1) Doppler echocardiography with the single-beat method developed by Chen et al (2001 J. Am. Coll. Cardiol. 38 2028-34); and (2) data provided by impedance cardiography. The differences between Ea/Ees values were compared and correlation between both methods was estimated.

Although Ea and Ees values calculated by impedance cardiography were lower than those estimated by echocardiography (-0.201  ±  0.457 mmHg ml^-1 and  -0.193  ±  0.413 mmHg ml^-1), Ea/Ees ratio values were similar. Thus, there was no significant difference between the mean values of Ea/Ees estimated by impedance cardiography or echocardiography (Ea/Ees impedance cardiography  -  Ea/Ees echocardiography  =  -0.015  ±  0.096, p   =  0.150). Ea/Ees values calculated by both methods were highly correlated (r  =  0.85, p   <  0.001), as well as the pre-ejection and left ventricular ejection time (r  =  0.83 and r  =  0.91, respectively).

In healthy individuals, estimation of Ea/Ees by impedance cardiography yielded similar values to those obtained using echocardiography.