Myocardial strain rate is a superior method for evaluation of left ventricular subendocardial function compared with tissue Doppler imaging.
OBJECTIVE
This study was performed to evaluate subendocardial function using strain rate imaging (SRI).


BACKGROUND
The subendocardium and mid-wall of the left ventricle (LV) play important roles in ventricular function. Previous methods used for evaluating this function are either invasive or cumbersome. Strain rate imaging by ultrasound is a newly developed echocardiographic modality based on tissue Doppler imaging (TDI) that allows quantitative assessment of regional myocardial wall motion.


METHODS
We examined eight sheep using TDI in apical four-chamber views to evaluate the LV free wall. Peak strain rates (SRs) during isovolumic relaxation (IR), isovolumic contraction (IC), and myocardial strain were measured in the endocardial (End), mid-myocardial (Mid), and epicardial (Epi) layers. For four hemodynamic conditions (created after baseline by blood, dobutamine, and metoprolol infusion), we compared differences in SR of End, Mid, and Epi layers to peak positive and negative first derivative of LV pressure (dP/dt).


RESULTS
Strain rate during IC showed a good correlation with +dP/dt (r = 0.74, p < 0.001) and during IR with -dP/dt (r = 0.67, p = 0.0003). There was a significant difference in SR between the myocardial layers during both IC and IR (End: -3.4 +/- 2.2 s(-1), Mid: -1.8 +/- 1.5 s(-1), Epi: -0.63 +/- 1.0 s(-1), p < 0.0001 during IC; End: 2.2 +/- 1.5 s(-1), Mid: 1.0 +/- 0.8 s(-1), Epi: 0.47 +/- 0.64 s(-1), p < 0.0001 during IR). Also, SRs of the End and Mid layers during IC were significantly altered by different hemodynamic conditions (End at baseline: 1.7 +/- 0.7 s(-1); blood: 2.0 +/- 1.1 s(-1); dobutamine: 3.4 +/- 2.3 s(-1); metoprolol: 1.0 +/- 0.4 s(-1); p < 0.05). Myocardial strain showed differences in each layer (End: -34.3 +/- 12.6%; Mid: -22.6 +/- 12.1%; Epi: -11.4 +/- 7.9%; p < 0.0001) and changed significantly in different hemodynamic conditions (p < 0.0001).


CONCLUSIONS
Strain and SR appear useful and sensitive for evaluating myocardial function, especially for the subendocardial region.
Hashimoto
Ikuo
I
Clinical Care Center for Congenital Heart Disease, Oregon Health and Sciences University, Portland, Oregon 97239, USA.
Li
Xiaokui
X
Hejmadi Bhat
Aarti
A
Jones
Michael
M
Zetts
Arthur D
AD
Sahn
David J
DJ
D000818:Animals; D002316:Cardiotonic Agents; D004280:Dobutamine; D015150:Echocardiography, Doppler / Q000379:methods*; D004699:Endocardium / Q000502:physiology; D006352:Heart Ventricles / Q000000981:diagnostic imaging; D006439:Hemodynamics; D007091:Image Processing, Computer-Assisted; D016014:Linear Models; D008790:Metoprolol; D009200:Myocardial Contraction; D012756:Sheep; D016277:Ventricular Function, Left
D002316:Cardiotonic Agents; D004280:Dobutamine; D008790:Metoprolol