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 (Emax) 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 (Sm) and peak (ε′p) and mean (ε′m) strain rates obtained at the basal septum were compared against Emax by linear regression. Emax 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 Emax 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 Sm (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 Sm, perhaps by eliminating translational artifact.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine
- Physiology (medical)