Prognostic Value of the Index of Microcirculatory Resistance Measured After Primary Percutaneous Coronary Intervention

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Abstract

BACKGROUND: Most methods for assessing microvascular function are not readily available in the cardiac catheterization laboratory. The aim of this study is to determine whether the Index of Microcirculatory Resistance (IMR), measured at the time of primary percutaneous coronary intervention (PCI) is predictive of death and rehospitalization for heart failure. METHODS AND RESULTS: IMR was measured immediately after primary PCI in 253 patients from 3 institutions using a pressure-temperature sensor wire. The primary endpoint was the rate of death or rehospitalization for heart failure. The prognostic value of IMR was compared to coronary flow reserve, TIMI myocardial perfusion grade and clinical variables. The mean IMR was 40.3 ±32.5. Patients with an IMR>40 had a higher rate of the primary end point at one year compared to patients with an IMR=40 (17.1% vs. 6.6%, p=0.027). During a median follow-up period of 2.8 years, 13.8% suffered the primary end point and 4.3% died. An IMR>40 was associated with an increased risk of death or rehospitalization for heart failure (HR 2.1, p=0.034) and of death alone (HR 3.95, p=0.028). On multivariate analysis, independent predictors of death or rehospitalization for heart failure included IMR>40 (HR 2.2, p=0.026), fractional flow reserve =0.8 (HR 3.24, p=0.008) and diabetes (HR 4.4, p<0.001). An IMR>40 was the only independent predictor of death alone (HR 4.3, p=0.02). CONCLUSIONS: An elevated IMR at the time of primary PCI predicts poor long term outcomes.

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