C oronary artery disease accounts for ≈1 in every 6 deaths in the United States, with acute ST-segment-elevation myocardial infarction (STEMI) contributing significantly to the overall morbidity associated with this disease. 1 Postmortem studies in patients dying of myocardial infarction consistently demonstrate that the majority of STEMIs are triggered by rupture of a thin-fibrous cap overlying a lipidrich necrotic core. 2-5Intracoronary near-infrared spectroscopy (NIRS) is a catheter-based imaging modality developed and validated to detect lipid-rich plaques (LRPs) in patients undergoing coronary angiography. 6,7 In an exploratory analysis in a small number of STEMI patients, NIRS demonstrated large, significant differences in the lipid content between culprit and nonculprit segments.8 A potential NIRS signature of STEMI culprit lesions was identified, defined by a maximum lipid core burden index within a 4-mm coronary section (maxL-CBI 4mm ) being >400. These initial observations were limited by a modest sample size, single-center enrollment, and post hoc selection of the maxLCBI 4mm ≥400 threshold. This study was designed a priori to confirm the ability of NIRS to discriminate STEMI culprit from nonculprit segments and to determine the sensitivity and specificity of the maxLCBI 4mm ≥400 threshold. Secondary aims were to evaluate the ability of the NIRS block chemogram to differentiate culprit from nonculprit segments and to evaluate the regional deposition of lipid within coronary segments adjacent to the angiographically defined culprit segment.© 2016 American Heart Association, Inc. Objective-In a previous exploratory analysis, intracoronary near-infrared spectroscopy (NIRS) found the majority of culprit lesions in ST-segment-elevation myocardial infarction (STEMI) to contain a maximum lipid core burden index in 4 mm (maxLCBI 4mm ) of >400. This initial study was limited by a small sample size, enrollment at a single center, and post hoc selection of the maxLCBI 4mm ≥400 threshold. This study was designed a priori to substantiate the ability of NIRS to discriminate STEMI culprit from nonculprit segments and to confirm the performance of the maxLCBI 4mm ≥400 threshold. Approach and Results-At 2 centers in the United States and Sweden, 75 STEMI patients underwent intracoronary NIRS imaging after establishing thrombolysis in myocardial infarction 3 flow, but before stenting. Blinded core laboratory analysis defined the culprit segment as the 10-mm segment distal to the proximal angiographic culprit margin. The remaining vessel was divided into contiguous 10-mm nonculprit segments.

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