Doppler-derived myocardial systolic strain rate is a strong index of left ventricular contractility

Background - Myocardial fiber strain is directly related to left ventricular (LV) contractility. Strain rate can be estimated as the spatial derivative of velocities (dV/ds) obtained by tissue Doppler echocardiography (TDE). The purposes of the study were (1) to determine whether TDE-derived strain rate may be used as a noninvasive, quantitative index of contractility and (2) to compare the relative accuracy of systolic strain rate against TDE velocities alone. Methods and Results - TDE color M-mode images of the interventricular septum were recorded from the apical 4-chamber view in 7 closed-chest anesthetized mongrel dogs during 5 different inotropic stages. Simultaneous LV volume and pressure were obtained with a combined conductance-high-fidelity pressure catheter. Peak elastance (E_max) was determined as the slope of end-systolic pressure-volume relationships during caval occlusion and was used as the gold standard of LV contractility. Peak systolic TDE myocardial velocities (S_m) and peak (ε′_p) and mean (ε′_m) strain rates obtained at the basal septum were compared against E_max by linear regression. E_max as well as TDE systolic indices increased during inotropic stimulation with dobutamine and decreased with the infusion of esmolol. A stronger association was found between E_max and ε′_p (r=0.94, P<0.01, y=0.29x+0.46) and ε′_m (r=0.88, P<0.01) than for S_m (r=0.75, P<0.01). Conclusions - TDE-derived ε′_p and ε′_m are strong noninvasive indices of LV contractility. These indices appear to be more reliable than S_m, perhaps by eliminating translational artifact.