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CLINICAL RESEARCH: CARDIAC IMAGING

Edema as a Very Early Marker for Acute Myocardial Ischemia

A Cardiovascular Magnetic Resonance Study

Hassan Abdel-Aty, MD^_*, Myra Cocker, BSc^_*, Cheryl Meek, RN, John V. Tyberg, MD, PhD and Matthias G. Friedrich, MD^_*,_*

^_* Stephenson CMR Centre at the Libin Cardiovascular Institute of Alberta, Calgary, Alberta, Canada
Department of Physiology and Biophysics, University of Calgary, Calgary, Alberta, Canada

Manuscript received July 18, 2008; revised manuscript received October 6, 2008, accepted October 7, 2008.

^_* Reprint requests and correspondence: Dr. Matthias G. Friedrich, University of Calgary, Stephenson Cardiovascular Magnetic Resonance Centre, Foothills Hospital, Special Services Building, Suite 0700, 1403-29th Street NW, Calgary, Alberta T2N 2T9, Canada (Email: matthias.friedrich{at}ucalgary.ca).

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.

Key Words: cardiovascular magnetic resonance • acute myocardial ischemia • myocardial edema • myocardial infarction • myocardial viability

Abbreviations and Acronyms   CMR = cardiovascular magnetic resonance   CNR = contrast-to-noise ratio   ESWT = end-systolic wall thickening   MI = myocardial infarction   SI = signal intensity   SSFP = steady-state free precession

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