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CLINICAL STUDY: ECHOCARDIOGRAPHIC METHODS

Higher myocardial strain rates duringisovolumic relaxation phase than duringejection characterize acutely ischemic myocardium

Cristina Pislaru, MD^*,*, Peter C. Anagnostopoulos, MD, James B. Seward, MD, FACC, James F. Greenleaf, PhD^* and Marek Belohlavek, MD, PhD, FACC

^* Department of Physiology and Biophysics Rochester, Minnesota, USA
Division of Cardiovascular Diseases Internal Medicine, Mayo Clinic and Foundation, Rochester, Minnesota, USA

Manuscript received November 26, 2001; revised manuscript received May 30, 2002, accepted July 2, 2002.

^* Reprint requests and correspondence: Dr. Cristina Pislaru, Mayo Clinic, Ultrasound Research Laboratory, 200 First Street SW, Rochester, Minnesota 55905, USA.
Pislaru.Cristina{at}mayo.edu

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 (_sys) and postsystolic strain (_ps) were calculated by integrating systolic and postsystolic strain rates, respectively.

RESULTS: During ischemia, S_SR, E_SR, and _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 _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.

Abbreviations and Acronyms   ECG   electrocardiogram   ESR   peak strain rate during early filling phase   max   maximum strain   ps   postsystolic strain   sys   systolic strain   IVRSR   peak strain rate during the isovolumic relaxation phase   LAD   left anterior descending coronary artery   LCX   left circumflex coronary artery   LV   left ventricle/ventricular   PSS   postsystolic shortening   RCA   right coronary artery   SSR   peak strain rate during ejection   SRI   strain rate imaging   t-SSR   time to the onset of longitudinal shortening

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