Background-The aim of this study was to determine whether edema imaging by T2-weighted cardiac magnetic resonance (CMR) imaging could retrospectively delineate the area at risk in reperfused myocardial infarction. We hypothesized that the size of the area at risk during a transient occlusion would be similar to the T2-weighted hyperintense region observed 2 days later, that the T2-weighted hyperintense myocardium would show partial functional recovery after 2 months, and that the T2 abnormality would resolve over 2 months. Methods and Results-Seventeen dogs underwent a 90-minute coronary artery occlusion, followed by reperfusion. The area at risk, as measured with microspheres (9 animals), was comparable to the size of the hyperintense zone on T2-weighted images 2 days later (43.4Ϯ3.3% versus 43.0Ϯ3.4% of the left ventricle; PϭNS), and the 2 measures correlated (Rϭ0.84). The infarcted zone was significantly smaller (23.1Ϯ3.7; both PϽ0.001). To test whether the hyperintense myocardium would exhibit partial functional recovery over time, 8 animals were imaged on day 2 and 2 months later. Systolic strain was mapped with displacement encoding with stimulated echoes. Edema, as detected by a hyperintense zone on T2-weighted images, resolved, and regional radial systolic strain partially improved from 4.9Ϯ0.7 to 13.1Ϯ1.5 (Pϭ0.001) over 2 months. Conclusions-These findings are consistent with the premise that the T2 abnormality depicts the area at risk, a zone of reversibly and irreversibly injured myocardium associated with reperfused subendocardial infarctions. The persistence of postischemic edema allows T2-weighted CMR to delineate the area at risk 2 days after reperfused myocardial infarction.
Background
In HCM, myocardial abnormalities are commonly heterogeneous. Two patterns of LGE have been reported: a bright “confluent” and an intermediate intensity abnormality termed “diffuse,” each representing different degrees of myocardial scarring. We used MRI to study the relation between intramural cardiac function and the extent of fibrosis in HCM. The aim of this study was to determine whether excess collagen or myocardial scarring, as determined by late gadolinium enhancement (LGE) MRI, are the primary mechanisms leading to heterogeneous regional contractile function in patients with hypertrophic cardiomyopathy (HCM).
Methods and Results
Intramural left ventricular (LV) strain, transmural LV function, and regions of myocardial fibrosis/scarring were imaged in 22 patients with HCM using displacement encoding with stimulated echoes (DENSE), cine MRI and LGE. DENSE systolic strain maps were qualitatively and quantitatively compared with LGE images. Intramural systolic strain by DENSE was significantly depressed within areas of confluent and diffuse LGE but also in the core of the most hypertrophic non-enhanced segment (all p<0.001 vs. non-hypertrophied segments). DENSE demonstrated an unexpected inner rim of largely preserved contractile function and a non-contracting outer wall within hypertrophic segments in 91% of patients.
Conclusions
LGE predicted some but not all of the heterogeneity of intramural contractile abnormalities. This indicates that myocardial scarring or excess interstitial collagen deposition does not fully explain the observed contractile heterogeneity in HCM. Thus, myofibril disarray or other non-fibrotic processes affect systolic function in a large number of patients with HCM.
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