Angiography-Derived Index of Microcirculatory Resistance to Define the Risk of Early Discharge in STEMI

Background: Patients with ST-segment-elevation myocardial infarction but no coronary microvascular injury are at low risk of early cardiovascular complications (ECC). We aim to assess whether nonhyperemic angiography-derived index of microcirculatory resistance (NH-IMR_angio) could be a user-friendly tool to identify patients at low risk of ECC, potentially candidates for expedited care pathway and early hospital discharge.

Methods: Retrospective analysis of 2 independent, international, prospective, observational cohorts included 568 patients with ST-segment-elevation myocardial infarction. NH-IMR_angio was calculated based on standard coronary angiographic views with 3-dimensional-modeling and computational analysis of the coronary flow.

Results: Overall, ECC (a composite of cardiovascular death, cardiogenic shock, acute heart failure, life-threatening arrhythmias, resuscitated cardiac arrest, left ventricular thrombus, post-ST-segment-elevation myocardial infarction mechanical complications, and rehospitalization for acute heart failure or acute myocardial infarction at 30 days follow-up), occurred in 54 (9.3%) patients. NH-IMR_angio was significantly correlated with pressure/thermodilution-based index of microcirculatory resistance (r=0.607; P<0.0001) and demonstrated good accuracy in predicting ECC (area under the curve, 0.766 [95% CI, 0.706-0.827]; P<0.0001). Importantly, ECC occurred more frequently in patients with NH-IMR_angio ≥40 units (18.1% versus 1.4%; P<0.0001). At multivariable analysis, NH-IMR_angio provided incremental prognostic value to conventional clinical, angiographic, and echocardiographic features (adjusted-odds ratio, 14.861 [95% CI, 5.177-42.661]; P<0.0001). NH-IMR_angio<40 units showed an excellent negative predictive value (98.6%) in ruling out ECC. Discharging patients with NH-IMR_angio<40 units at 48 hours after admission would reduce the total in-hospital stay by 943 days (median 2 [1-4] days per patient).

Conclusions: NH-IMR_angio is a valuable risk-stratification tool in patients with ST-segment-elevation myocardial infarction. NH-IMR_angio guided strategies to early discharge may contribute to safely shorten hospital stay, optimizing resources utilization.