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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

View larger version (35K): [in a new window]   Figure 1 Representative strain rate and strain profiles at baseline and during ischemia. (a) Strain rate curves of the ischemic (apical) and nonischemic (basal) septal segments in an apical four-chamber view at baseline and during ischemia. Negative strain rate reflects shortening; positive strain rate reflects lengthening. The vertical lines in each image mark the time of the aortic valve opening and mitral valve closure, respectively. Peak strain rates were measured during ejection (SSR), isovolumic relaxation (IVRSR), and early filling (ESR); t-SSR represents the time to onset of longitudinal shortening (SSR). At baseline, negative IVRSR (postsystolic shortening) was found in the basal septal (nonischemic) segment. During occlusion, SSR decreased and t-SSR was delayed, while a prominent IVRSR developed in the ischemic segment, but not in the normally perfused segment. Importantly, IVRSR/SSR was >1 only in the ischemic segment. (b) The corresponding regional strain curves. Reduced systolic strain (sys) and increased postsystolic strain (ps) occurred in the ischemic segment. Conversely, a normal sequence of contraction/relaxation occurred in the nonischemic (basal) segment.

View larger version (54K): [in a new window]   Figure 2 Regional strain rate parameters during baseline and acute ischemia. A significant change in regional peak strain rate during ejection (SSR), isovolumic relaxation (IVRSR) and early filling (ESR) occurred in the ischemic segments (solid square) but not in normally perfused segments (open circle). No overlap between normal and ischemic was found for IVRSR/SSR ratio. Values from all 28 animals and all three perfusion territories are displayed, except for IVRSR/SSR (25 animals).

View larger version (25K): [in a new window]   Figure 3 Regional strain parameters at baseline and during ischemia. Systolic strain (sys) (left panel) was significantly reduced and even inverted (reflecting bulging), while postsystolic strain (ps) (right panel) significantly increased in the ischemic (solid square) but not in normally perfused segments (open circle). Some overlap between normal and ischemic sys and ps values was observed.

View larger version (70K): [in a new window]   Figure 4 Parametric images generated from strain rate data in two animals, one subjected to left anterior descending (LAD) and the other to right coronary artery (RCA) occlusion. Each manually delineated left ventricular wall (a and e) was divided into 10 segments (to increase the spatial resolution). Peak systolic strain rates (SSR) (b and f) and postsystolic-to-systolic strain rate ratio (IVRSR/SSR) (c and g) were calculated and used to generate corresponding parametric images. Ischemic myocardium was outlined as the region with reduced SSR, and IVRSR/SSR >1. Note the reduced systolic strain rates in the border zones, while the IVRSR/SSR is <1 in these segments. Panels d and h show the extent of perfusion defect at myocardial contrast echocardiography or postmortem staining.