Comparison of cardiac MR and 99mtc Sestamibi Spect in the evaluation of myocardial perfusion and viability in coronary artery disease

Abstract

Objective - The present study was designed to compare the role of 99mTc sestamibi sciintigraphy (SPECT) and cardiac MR (CMR) in the detection of viable myocardium and to delineate myocardial scar tissue in patients with established chronic ischemic heart disease. Methods - Thirty six patients with established chronic ischemic heart disease on coronary angiograms which was the gold standard underwent both stress CMR and 99mTc sestamibi studies. Out of these 11 patients who had reduced end diastolic thickness < 5.5mm alongwith wall motion abnormalities also underwent dobutamine MR (DMR) for determining the contractile myocardial reserve. Results- Both CMR and SPECT showed a good correlation in the detection of perfusion defects (r=0.89) with the diagnostic region of operating characteristics being 0.97. The sensitivity and specificity of SPECT to detect perfusion defects were 82.6% and 90.4% respectively. In comparison CMR had a sensitivity, specificity of 92.8% and 98.2% respectively in identifying such defects.It was also superior in defining transmural infarcts(TMI) with sensitivity being 100% vs 79.3% of SPECT (p=< 0.0001) and all the 10 segments with TMI showed irreversible myocardial dysfunction on DMR. This was the only imaging parameter that indicated myocardial non viability with a specificity of 100%. Conclusions - CMR is a useful diagnostic tool in the evaluation of patients with chronic myocardial ischemia and is superior to SPECT in the detection and quantification of myocardial infarctions. Demonstration of a TMI on CMR is a finding strongly associated with non viability of the myocardium and may preclude the need for doing a DMR in such cases.