Aims It is well accepted that strain and strain rate deformation parameters are not only a measure of intrinsic myocardial contractility but are also influenced by changes in cardiac load and structure. To date, no information is available on the relative importance of these confounders. The study was designed to investigate how strain and strain rate, measured by Doppler echocardiography, relate to the individual factors that determine cardiac performance. Methods and Results Echocardiographic and conductance measurements were simultaneously performed in mice in which individual determinants of cardiac performance were mechanically and/or pharmacologically modulated. A multivariable analysis was performed with radial and circumferential strains (Srad and Scirc) and peak systolic strain rates (SRrad and SRcirc) as dependent parameters, and preload recruitable stroke work (PRSW), arterial elastance (Ea), end diastolic pressure (EDP) and left ventricular myocardial volume (LVMV), as independent factors representing myocardial contractility, afterload, preload and myocardial volume respectively. Srad was most influenced by Ea (β=-0.58, R2=0.34), whereas Scirc was strongly associated with Ea and moderately with LVMV (β=0.79 and β=-0.52, respectively; R2=0.54). SRrad was related to both PRSW and LVMV (β=0.79 and β=-0.62; R2=0.50), while SRcirc showed a prominent correlation only with PRSW (β=-0.61, R2=0.51). Conclusions Strain (both radial and circumferential) is not a good surrogate measure of intrinsic myocardial contractility unless the strong confounding influence of afterload is considered. Strain rate is a more robust measure of contractility which is less influenced by changes in cardiac load and structure. Thus, peak systolic strain rate is the more relevant parameter to assess myocardial contractile function non-invasively.
- strain rate
- tissue Doppler imaging
- Copyright © 2011, American Journal of Physiology - Heart and Circulatory Physiology