Clinical study: echocardiographic methods
Higher myocardial strain rates duringisovolumic relaxation phase than duringejection characterize acutely ischemic myocardium

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Abstract

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 (SSR), isovolumic relaxation (IVRSR), and rapid filling (ESR) phases in both ischemic and normal myocardium. Systolic strain (ϵsys) and postsystolic strain (ϵps) were calculated by integrating systolic and postsystolic strain rates, respectively.

Results

During ischemia, SSR, ESR, and ϵsys 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 IVRSR (i.e., PSS) in at least one segment. During coronary artery occlusion, IVRSR became negative and larger in magnitude than SSR in all ischemic segments. The IVRSR/SSR and ϵps 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

ECG
electrocardiogram
ESR
peak strain rate during early filling phase
ϵmax
maximum strain
ϵps
postsystolic strain
ϵsys
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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Supported in part by grants from the National Institutes of Health (HL41046) and GE Medical Systems (Milwaukee, Wisconsin).