Non-Q-wave myocardial infarction: impaired myocardial energy metabolism inregions with reduced Tc-99m-MIBI accumulation

Reduced regional technetium-99m methoxyisobutylisonitrile (Tc-99m-MIBI) acc umulation in patients with chronic non-Q-wave infarction (NQWI) but without significant coronary artery stenosis indicates non-transmural damage of th e myocardial wall. The aim of this study was to characterise cardiac energy metabolism after NQWI using phosphorus-31 magnetic resonance spectroscopy (P-31-MRS) and to compare the biochemical remodelling with changes in regio nal Tc-99m-MIBI uptake and with morphological and functional parameters ass essed by magnetic resonance imaging (MRI). Fifteen patients with a history of NQWI, exclusion of significant coronary artery stenosis (<50% diameter s tenosis) and hypokinesia of the anterior wall (group A) were examined with P-31-MRS to study the effects of NQWI on myocardial energy metabolism. Spec troscopic measurements were performed in the infarct-related myocardial reg ion. Corresponding gradient-echo MR images and myocardial Tc-99m-MIBI singl e-photon emission tomography images were acquired for exact localisation of the infarct region. All examinations were performed at rest under anti-isc haemic medication. Data were compared with those of patients in whom corona ry artery disease had been excluded by angiography (group B, n=10). All pat ients of group A displayed anterior wall hypokinesia in the infarcted area on both ventriculography and MRI, with a reduced myocardial accumulation of Tc-99m-MIBI (66.3%+/-11.8% vs 95.6%+/-2.2% in group B). The mean wail thic kness during the complete cardiac cycle (9.5+/- 1.8 mm vs 13.1+/-1.1 mm in group B, P<0.001), the systolic wall thickening (2.6+/-1.4 mm vs 5.8+/-1.5 mm in group B, P<0.01) and the phosphocreatine/adenosine triphosphate ratio (1.12+/-0.22 vs 1.74+/-0.23 in group B, P<0.01) in the hypokinetic area we re all significantly reduced. It is concluded that persisting hypokinetic m yocardium after NQWI combined with reduced myocellular uptake of Tc-99m-MIB I displays a reduced PCr/ATP ratio. Our results indicate that morphological remodelling after NQWI is accompanied by fundamental changes in cardiac en ergy metabolism.