A CMR study of the Effects of Tissue Edema and Necrosis on Left Ventricular Dyssynchrony in Acute Myocardial Infarction: Implications for Cardiac Resynchronization Therapy
OBJECTIVES: In acute myocardial infarction (AMI), both tissue necrosis and edema are present and both might be implicated in the development of intraventricular dyssynchrony. However, their relative contribution to transient dyssynchrony is not known. Cardiac magnetic resonance (CMR) can detect necrosis and edema with high spatial resolution and it can quantify dyssynchrony by tagging techniques.
METHODS: Patients with a first AMI underwent percutaneous coronary interventions (PCI) of the infarct-related artery within 24 h of onset of chest pain. Within 5-7 days after the event and at 4 months, a CMR study was performed. The CMR protocol included the evaluation of intraventricular dyssynchrony by applying a novel 3D-tagging sequence to the left ventricle (LV) yielding the CURE index (circumferential uniformity ratio estimate; 1=complete synchrony). On T2-weighted images, edema was measured as high-signal (>2 SD above remote tissue) along the LV mid-myocardial circumference on 3 short-axis images (% of circumference corresponding to the area-at-risk). In analogy, on late-gadolinium enhancement (LGE) images, necrosis was quantified manually as percentage of LV mid-myocardial circumference on 3 short-axis images. Necrosis was also quantified on LGE images covering the entire LV (expressed as %LV mass). Finally, salvaged myocardium was calculated as the area-at-risk minus necrosis (expressed as % of LV circumference).
RESULTS: After successful PCI (n=22, 2 female, mean age: 57+/-12y), peak troponin T was 20+/-36ug/l and the LV ejection fraction on CMR was 41+/-8%. Necrosis mass was 30+/-10% and CURE was 0.91+/-0.05. Edema was measured as 58+/-14% of the LV circumference. In the acute phase, the extent of edema correlated with dyssynchrony (r2=-0.63, p<0.01), while extent of necrosis showed borderline correlation (r2=-0.19, p=0.05). PCI resulted in salvaged myocardium of 27+/-14%. LV dyssynchrony (=CURE) decreased at 4 months from 0.91+/-0.05 to 0.94+/-0.03 (p<0.004, paired t-test). At 4 months, edema was absent and scar %LV slightly shrunk to 23.7+/-10.0% (p<0.002 vs baseline). Regression of LV dyssynchrony during the 4 months follow-up period was predicted by both, the extent of edema and its necrosis component in the acute phase.
CONCLUSIONS: In the acute phase of infarction, LV dyssynchrony is closely related to the extent of edema, while necrosis is a poor predictor of acute LV dyssynchrony. Conversely, regression of intraventricular LV dyssynchrony during infarct healing is predicted by the extent of necrosis in the acute phase.
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