RESUMO
OBJECTIVES: This study was designed to determine whether imaging myocardial edema would identify acute myocardial ischemia before irreversible injury takes place. BACKGROUND: Early identification of acute myocardial ischemia is a diagnostic challenge. METHODS: We studied 15 dogs with serial T(2)-weighted and cine imaging at baseline, during transient coronary occlusion of up to 35 min, and after reperfusion in a 1.5-T magnetic resonance imaging system. Late gadolinium enhancement and troponin measurements were used to assess for the presence of irreversible injury. Myocardial water content was measured to assess myocardial edema. RESULTS: We consistently observed a transmural area of high T(2) signal intensity matching areas with new onset regional akinesia 28 +/- 4 min after experimental coronary artery occlusion. At this time, the contrast-to-noise ratio between the ischemic and remote myocardium had significantly increased from 1.0 +/- 2.0 to 12.8 +/- 9.6 (p < 0.003), which further increased after reperfusion to 15.8 +/- 10.3 (p < 0.004 compared with baseline). Neither myocardial late gadolinium enhancement nor troponin elevation were noted at this time window. Myocardial water content of the ischemic segments was consistently higher (68.9 +/- 2% vs. 67.0 +/- 2%; p < 0.004) than in remote segments and the difference correlated significantly to the contrast-to-noise ratio in T(2) images (p < 0.04). CONCLUSIONS: We provide the first evidence that T(2)-weighted cardiovascular magnetic resonance imaging of edema detects acute ischemic myocyte injury before the onset of irreversible injury. T(2)-weighted cardiovascular magnetic resonance imaging may serve as a very useful diagnostic marker in clinical settings such as unstable angina or evolving infarction.
