Purpose: Inferior attenuation is a common problem in the interpretation of myocardial perfusion SPECT. We explored whether cardiovascular magnetic resonance (CMR) was a useful adjunct in differentiating between artifactual attenuation of the inferior wall and the presence of myocardial infarction and/or ischemia.
Methods: We used CMR to assess resting wall motion, myocardial perfusion, and the presence of infarction with late gadolinium enhancement in 30 patients with presumed inferior attenuation on ungated myocardial perfusion SPECT, but where uncertainty was present over interpretation of the inferior wall. Perfusion CMR was analyzed visually and quantitatively.
Results: In 23 patients (77%), CMR excluded infarction or ischemia in the inferior wall. The myocardial perfusion reserve index (MPR1) was the same in the inferior and remote myocardium (1.74 +/- 0.43 vs. 1.77 +/- 0.50, p = 0.61). Coronary angiography was performed in 11 of these patients, and was normal in all cases. In the remaining seven subjects (23%), significant abnormality was detected by CMR (infarction, 5; wall motion abnormality, 3; perfusion defect, 5). In these patients, the MPR1 was reduced in the inferior myocardium compared with remote (1.07 +/- 0.19 vs. 1.74 +/- 0.49, p = 0.04). Coronary angiography was performed in three of these patients, revealing significant coronary disease in the artery supplying the inferior territory in all patients.
Conclusion: Approximately one-quarter of patients with inferior attenuation on ungated, nonattenuation corrected myocardial perfusion SPECT have abnormalities on CMR. CMR can readily distinguish between artifact, ischemia, and infarction in these cases and in some cases might obviate the need for diagnostic coronary angiography.