Regional 99mTc-methoxyisobutyl-isonitrile-uptake at rest in patients with myocardial infarcts: comparison with morphological and functional parameters obtained from gradient-echo magnetic resonance imaging

It is not yet clear whether 99mTc-methoxyisobutyl-isonitrile (MIBI)-uptake is a reliable indicator of myocardial viability, and a threshold value, differentiating viable from scarred myocardium, in comparison to a morphological and functional standard of reference has not been defined. MIBI-uptake was quantified in 800 segments from 55 patients with angiographically proven coronary artery disease with and without a history of myocardial infarction. Viable myocardium was defined from gradient-echo magnetic resonance images (MRI) as regions with systolic wall thickening or an end-diastolic wall thickness above the mean value -2.5 SD of a healthy control group (n = 21). Scar was defined as end-diastolic wall thickness > 2.5 SD below the normal mean value and absent systolic wall thickening or wall thinning. Mean MIBI-uptake of viable (n = 676; 79 +/- 14%) and scar segments by MRI (n = 124; 31 +/- 16%) was significantly different (P < 0.001). Segmental MIBI-uptake vs end-diastolic wall thickness (r = 0.7) and systolic wall thickening (r = 0.71) yielded a fair correlation. The highest values as regards sensitivity and specificity of MIBI-uptake in predicting the presence of scar were 89% and 96% respectively for MIBI-uptake < or = 50%. However, of the 136 segments with MIBI-uptake < or = 50%, 26 (19%) were viable by MRI, resulting in a positive predictive accuracy for scar tissue of 81%. Of the 26 segments diagnosed as scarred by MIBI-SPECT but viable by MRI, 25 (96%) were located in the inferoseptal region. MIBI-SPECT seems useful in the detection of viable myocardium after anterior myocardial infarcts, but over-estimates scar in the inferoseptal regions. Perfusion defects in these regions could be confirmed or denied by additional evaluation of myocardial morphology and function by MRI or tissue metabolism by positron emission tomography (PET).