Regional asynchrony during acute myocardial ischemia quantified by ultrasound strain rate imaging

We propose a new method to easily quantify asynchronous wall motion due to postsystolic shortening (PSS). We also studied the relationship of the spatial and temporal extent of PSS to the extent of myocardium at ischemic risk after variable duration of ischemia.

Postsystolic shortening is a sensitive marker of asynchrony during ischemia. Current techniques for detection of asynchrony are either subjective, or invasive and time-consuming. Strain rate imaging (SRI) can noninvasively depict PSS as prolonged compression/expansion crossover.

Nineteen open-chest pigs were scanned from apical views, before and after left anterior descending coronary artery occlusion. Strain rates were derived offline from tissue Doppler velocity cineloops. The time from electrocardiographic R-wave to the occurrence of compression/expansion crossover (TCEC) was calculated. Prolonged TCEC during ischemia was identified using a standardized analysis and both spatial (% of left ventricle) and temporal extent were quantified. The extent of myocardium at risk was measured in seven animals from dye-stained specimens.

Prolonged TCEC was found in all ischemic segments. There was a good correlation (r = 0.91; p < 0.001) and good agreement between the spatial distributions of prolonged TCEC and myocardium at risk. The extent of myocardium at risk was better approximated by TCEC measurement (36 +/- 7% vs. 39 +/- 8%, respectively; p = NS) than by wall motion analysis (47 +/- 17%, p < 0.05). The duration of occlusion did not prolong TCEC.

Prolonged TCEC consistently occurs in ischemic myocardium and is apparently not affected by the duration of ischemia. Standardized analysis of TCEC in SRI closely quantifies the extent of ischemic myocardium. This new method may be a useful tool in other cardiac conditions associated with regional diastolic asynchrony.