Functional Coronary Angiography–Derived Index of Microcirculatory Resistance in Patients With ST-Segment Elevation Myocardial Infarction

Objectives: The aim of this study was to evaluate the diagnostic accuracy and prognostic implications of angiography-derived index of microcirculatory resistance (angio-IMR) in patients with ST-segment elevation myocardial infarction (STEMI). Background: The index of microcirculatory resistance (IMR) is a reliable invasive measure of coronary microvascular dysfunction in patients with STEMI. A functional coronary angiography–derived method to estimate IMR is a wire- and hyperemic agent–free alternative to IMR. Methods: The study population consisted of 2 independent cohorts. The diagnostic cohort comprised patients with IMR from the culprit vessel immediately after successful primary percutaneous coronary intervention (n = 31). The prognostic cohort was patients with STEMI who were successfully treated with primary percutaneous coronary intervention and followed for 10 years from the index procedure (n = 309). Angio-IMR was calculated using computational flow and pressure simulation. The primary outcome was a composite of cardiac death and readmission for heart failure over 10 years of follow-up. Results: In the diagnostic cohort, angio-IMR correlated well with IMR (R = 0.778; P < 0.001). Sensitivity, specificity, accuracy, and area under the curve of angio-IMR to predict IMR >40 U were 75.0%, 84.2%, 80.6%, and 0.899 (95% confidence interval: 0.786-0.949), respectively. In the prognostic cohort, patients with angio-IMR >40 U showed significantly higher risk for cardiac death or readmission for heart failure than did those with angio-IMR ≤40 U (46.7% vs 16.6%; adjusted hazard ratio: 2.909; 95% CI: 1.670-5.067; P < 0.001). Angio-IMR >40 U was an independent predictor of cardiac death or readmission for heart failure (hazard ratio: 2.173; 95% CI: 1.157-4.079; P = 0.016) and showed incremental prognostic value compared with a model with clinical risk factors only (C index = 0.726 vs 0.666 [P < 0.001], net reclassification index = 0.704 [P < 0.001]). Conclusions: Angio-IMR showed high correlation and diagnostic accuracy to predict IMR. Patients with STEMI with angio-IMR >40 U showed a significantly higher risk for cardiac death or readmission for heart failure than those with preserved angio-IMR values.