Comparison of Echocardiographic Indices of Myocardial Strain to Invasive Measurements of Left Ventricular Systolic Function
Strain and strain rate (SR) are recently developed echocardiographic indices of regional myocardial systolic function that are relatively unaffected by passive motion, cardiac translation, and tethering effects. Unlike Doppler-derived strain and SR, two-dimensional (2D) techniques are angle-independent.
This prospective study tested the hypothesis that 2D strain analysis of longitudinal and radial strain and SR can predict an invasive, gold-standard measure of global left ventricular (LV) systolic function (+dP/dtmax) over a range of hemodynamic and inotropic states. Simultaneous cardiac catheterization and Doppler echocardiography were performed in seven healthy, anesthetized dogs. Measurements of 2D-derived strain variables, conventional echocardiographic indices of LV systolic function, and LV +dP/dtmax were compared over six treatment periods that altered loading and inotropic conditions. Statistical methods included linear regression and calculation of Pearson's or Spearman's correlation coefficients.
One hundred percent of myocardial segments could be analyzed. Linear relationships were identified between 2D-derived strain variables and LV +dP/dtmax with longitudinal SR and global strain demonstrating the strongest correlations (r>0.75, P<0.0001). Correlation of traditional echocardiographic indices of LV systolic function with LV +dP/dtmax were lower (r <0.74, P <0.0001). Correlations between global longitudinal strain and traditional echocardiographic indices of LV systolic function were relatively low (all r <0.70, P <0.0001) except for LV ejection fraction (r = -0.876).
These results indicate that 2D strain and SR may represent useful noninvasive indices of LV systolic function in dogs. Further studies are needed to develop reference ranges and assess repeatability in healthy canine populations and to assess this methodology in dogs with cardiac disease.