Higher myocardial strain rates during isovolumic relaxation phase than during ejection characterize acutely ischemic myocardium

OBJECTIVES: The aim of this study was to define an index that can differentiate normal from ischemic myocardial segments that exhibit postsystolic shortening (PSS). BACKGROUND: Identification of ischemia based on the reduction of regional systolic function is sometimes challenging because other factors such as normal nonuniformity in contraction between segments, tethering effect, pharmacologic agents, or alterations in loading conditions can also cause reduction in regional systolic deformation. The PSS (contraction after the end of systole) is a sensitive marker of ischemia; however, inconsistent patterns have also been observed in presumed normal myocardium. METHODS: Twenty-eight open-chest pigs underwent echocardiographic study before and during acute myocardial ischemia induced by coronary artery occlusion. Ultrasound-derived myocardial longitudinal strain rates were calculated during systole (S_SR), isovolumic relaxation (IVR_SR), and rapid filling (E_SR) phases in both ischemic and normal myocardium. Systolic strain (ε_sys) and postsystolic strain (ε_ps) were calculated by integrating systolic and postsystolic strain rates, respectively. RESULTS: During ischemia, S_SR, E_SR, and ε_sys in ischemic segments were significantly lower (in magnitude) than in nonischemic segments or at baseline. However, some overlap occurred between ischemic and normal values for all three parameters. At baseline, 18 of 28 animals had negative IVR_SR (i.e., PSS) in at least one segment. During coronary artery occlusion, IVR_SR became negative and larger in magnitude than S_SR in all ischemic segments. The IVR_SR/S_SR and ε_ps best differentiated ischemic from nonischemic segments. CONCLUSIONS: In the presence of reduced regional systolic deformation, a higher rate of PSS than systolic shortening identifies acutely ischemic myocardium.