OBJECTIVES The aim of this study was to evaluate the diagnostic accuracy and prognostic implications of angiographyderived
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 ¼ 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 ¼ 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 ¼ 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 ¼ 0.016) and showed incremental
prognostic value compared with a model with clinical risk factors only (C index ¼ 0.726 vs 0.666 [P < 0.001],
net reclassification index ¼ 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. (Prognostic Implication of Angiography-Derived IMR in STEMI Patients; NCT04628377)
(J Am Coll Cardiol Intv 2021;14:1670?84) ⓒ 2021 by the American College of Cardiology Foundation
