Edema as a Very Early Marker for Acute Myocardial Ischemia. A Cardiovascular Magnetic Resonance Study

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 T₂-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 T₂ 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 T₂ images (p < 0.04). Conclusions: We provide the first evidence that T₂-weighted cardiovascular magnetic resonance imaging of edema detects acute ischemic myocyte injury before the onset of irreversible injury. T₂-weighted cardiovascular magnetic resonance imaging may serve as a very useful diagnostic marker in clinical settings such as unstable angina or evolving infarction.