Non-Q-wave myocardial infarction: impaired myocardial energy metabolism in regions with reduced ^99mTc-MIBI accumulation

Abstract.

Reduced regional technetium-99m methoxyisobutylisonitrile (^99mTc-MIBI) accumulation in patients with chronic non-Q-wave infarction (NQWI) but without significant coronary artery stenosis indicates non-transmural damage of the myocardial wall. The aim of this study was to characterise cardiac energy metabolism after NQWI using phosphorus-31 magnetic resonance spectroscopy (³¹P-MRS) and to compare the biochemical remodelling with changes in regional ^99mTc-MIBI uptake and with morphological and functional parameters assessed by magnetic resonance imaging (MRI). Fifteen patients with a history of NQWI, exclusion of significant coronary artery stenosis (<50% diameter stenosis) and hypokinesia of the anterior wall (group A) were examined with ³¹P-MRS to study the effects of NQWI on myocardial energy metabolism. Spectroscopic measurements were performed in the infarct-related myocardial region. Corresponding gradient-echo MR images and myocardial ^99mTc-MIBI single-photon emission tomography images were acquired for exact localisation of the infarct region. All examinations were performed at rest under anti-ischaemic medication. Data were compared with those of patients in whom coronary artery disease had been excluded by angiography (group B, n=10). All patients of group A displayed anterior wall hypokinesia in the infarcted area on both ventriculography and MRI, with a reduced myocardial accumulation of ^99mTc-MIBI (66.3%±11.8% vs 95.6%±2.2% in group B). The mean wall thickness 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 were all significantly reduced. It is concluded that persisting hypokinetic myocardium after NQWI combined with reduced myocellular uptake of ^99mTc-MIBI displays a reduced PCr/ATP ratio. Our results indicate that morphological remodelling after NQWI is accompanied by fundamental changes in cardiac energy metabolism.