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Contrast-Enhanced Cardiovascular Magnetic Resonance Finds Very Small Infarcts
Lancet
01/30/2003
By Harvey McConnell
A new technique based on contrast-enhanced cardiovascular magnetic resonance (CMR) can detect infarcts missed by the usual single photon emission computed tomography (SPECT).
This is demonstrated in a study from Northwestern University Medical School Feinberg Cardiovascular Research Institute, Chicago, Illinois, and the Duke Cardiovascular Magnetic Resonance Center, in Durham, North Carolina. Researchers compared CMR and SPECT examinations in 91 patients with suspected or known coronary artery disease.
SPECT myocardial perfusion imaging is an established procedure, the investigators point out, but some studies suggest that it misses small infarcts. CMR is a new technique that allows visualization of transmural and subendocardial myocardial infarcts.
Over an 18 month period, investigators consecutively enrolled patients who underwent clinically indicated stress-rest SPECT perfusion imaging for known or suspected coronary artery disease. They were also studied by contrast-enhanced CMR. Known coronary artery disease was defined as a 50% or greater stenosis in one or more of the coronary arteries at cardiac catheterisation, or a history of myocardial infarction, or both.
Investigators found that in the patients, all segments with nearly transmural infarction, as defined by contrast-enhanced CMR, were detected by SPECT. However, of the 181 segments with subendocardial infarction, 85 (47%) were not detected by SPECT. On a per patient basis, six (13%) individuals with subendocardial infarcts visible by CMR had no evidence of infarction by SPECT.
The researchers said a possible reason for this lack of sensitivity is that the spatial resolution of SPECT images (about 10 mm) is comparable with the thickness of the heart wall. Thus subendocardial infarcts, which by definition do not involve the entire heart wall, are beyond the spatial resolution . Conversely, CMR typically yields 5 to 10 pixels within the heart wall, making it possible to see subendocardial infarcts.
Further investigation is needed to ascertain the appropriate treatment for patients with subendocardial infarcts that can only be detected by CMR, they conclude.
Lancet 2003;361:374-79.
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