Accurately Defines Infarct Size, But Not Microvascular Obstruction After Myocardial Infarction

To the Editor: Early percutaneous coronary intervention (PCI) andreperfusion of obstructed epicardial arteries have improved patientsurvival after myocardial infarction (MI), but downstream, microvas-cularobstruction(MVO)remainsasignificantnegativepredictorafteracute infarct PCI (1). Recently, it has been suggested that dynamiccontrast-enhanced multidetector computed tomography (MDCT)may be equally effective as magnetic resonance imaging (MRI) inpredicting MVO in the clinical setting (2), but evidence validatingthis contention is scant. Nitrite ions are microvascular vasodilators,and have been demonstrated to reduce MRI-defined MVO, and toimprove endocardial blood flow in a large-animal MI model, verifiedusing the accepted gold standard: thioflavin S exclusion (TSE) todefineMVOandmicrosphereanalysistomeasureregionalbloodflow(RBF) (3).The purpose of this study was: 1) to correlate putative MVO contrastattenuation patterns (hypoenhancement area on MDCT image) withMVO derived from ex vivo TSE and RBF assessment; and 2) todetermine whether nitrite-induced dynamic changes in MVO could beequally detected using RBF assessment and MDCT image analysis.Sixteen female, 25 kg to 30 kg, Landrace pigs (of which 12survived: 6 in the saline group; 6 in the nitrite group) underwentexperimental MI by balloon occlusion of the mid left anteriordescendingarteryfor90minfollowedbyreperfusionfor2h(4). Afterballoon deflation, MDCT and microsphere delivery were performed atthesametimepoint.Areasofhyperenhancementandhypoenhancementwere determined using a 5-min delayed enhancement scan. The numberof microspheres detected in each region of the heart, corrected for aorticblood flow, provided RBF for that region for each condition (5 ). Nitritediluted in saline (0.2 mol · min