CMR May Be an Alternative to SPECT for Assessing Myocardial Salvage Following PCI

Cardiac magnetic resonance (CMR) with T2-weighted imaging and late-enhancement imaging correlates well with single-photon emission computed tomography (SPECT) for the assessment of area at risk, scar size and salvage area after percutaneous coronary intervention (PCI) for acute myocardial infarction, and CMR might be an alternative to the established SPECT modality, according to a study published March 4 in the Journal of the American College of Cardiology: Cardiovascular Imaging.

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The study analyzed the extent of myocardial salvage in 180 patients who underwent both imaging modalities following PCI. Results showed that mean area at risk was 29.4 ± 18.7 percent of the left ventricle (LV), and infarct size was 14.7 ± 16.9 percent LV, resulting in a mean salvage area of 14.9 ± 15.1 percent LV in SPECT, whereas in CMR, mean area at risk was 28.0 ± 14.5 percent LV, and infarct size was 16.0 ± 13.5 percent LV, resulting in a mean salvage area of 11.9 ± 12.3 percent. Results of both imaging studies were well correlated well for area at risk (r = 0.80), scar size (r = 0.87), and salvage area (r = 0.66, all p < 0.0001).

The authors note that some divergence was observed between the technologies, and they found "a reasonably good correlation between the two modalities; but in 38 percent of the patients, the results of both methods diverged by more than 10 percent of the left ventricle volume, a difference that may be clinically significant."

Nevertheless, they conclude, "we could demonstrate that the assessment of the area at risk by T2-weighted CMR imaging in CMR correlates well with the established modality of SPECT in patients undergoing primary PCI in acute myocardial infarction. CMR may therefore be an alternative to paired SPECT imaging for myocardial salvage assessment."

In an accompanying editorial, Ami E. Iskandrian, MACC, University of Alabama at Birmingham, and Fadi G. Hage, MD, FACC, Birmingham Veterans Administration Medical Center, Birmingham, Ala., congratulated the investigators for "providing correlative data on a large sample size, especially since assessment of area at risk is not routinely done for clinical care." They also noted that CMR, unlike SPECT, does not require potentially harmful radiation exposure or pre- and post-interventional scans. CMR requires only one examination. However, the commentators also note that CMR is contraindicated in patients with pacemakers and defibrillators, and that it is difficult to perform in patients with claustrophobia.

"Thus, although MRI may offer an alternative to myocardial perfusion imaging for myocardial salvage assessment, contraindications of this modality and limitations in the currently established imaging sequences may cause a considerable rate of data loss, which prevents widespread clinical applicability," they wrote.

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