Combination of the Thermodilution-Derived Index of Microcirculatory Resistance and Coronary Flow Reserve Is Highly Predictive of Microvascular Obstruction on Cardiac Magnetic Resonance Imaging After ST-Segment Elevation Myocardial Infarction.

OBJECTIVES: The aim of this study was to investigate the predictive accuracy of invasive coronary microvascular indexes for identifying microvascular obstruction (MVO) on cardiac magnetic resonance imaging (CMR) in patients treated with primary percutaneous coronary intervention (PCI) for ST-segment elevation myocardial infarction (STEMI).

BACKGROUND: We hypothesized that a combination of the index of microcirculatory resistance (IMR) and the thermodilution-derived coronary flow reserve (CFRthermo) will enhance the predictive accuracy of detecting MVO compared with either index alone.

METHODS: The IMR and CFRthermo were measured using a single pressure sensor/thermistor-tipped guidewire in 40 STEMI patients immediately after PCI and related to MVO assessed by CMR day 7. The primary endpoint was the predictive accuracy of the IMR for detecting MVO.

RESULTS: Patients with an IMR >36 (upper tertile) had a higher rate of MVO compared with those with an IMR ≤36 (93% vs. 39%; p = 0.001). MVO occurred in all patients with an IMR >36 and a CFRthermo ≤1.7 and in no patients with an IMR ≤36 and a CFRthermo >1.7. The IMR remained an independent predictor of MVO (odds ratio: 1.212, 95% confidence interval [CI]: 1.004 to 1.464; p = 0.045) after adjustment for age, creatine kinase-myocardial band, myocardial blush grade, thrombus burden, and CFRthermo. Both the IMR (area under the curve, 0.868, 95% CI: 0.719 to 0.956; p = 0.001) and the CFRthermo (area under the curve, 0.706, 95% CI: 0.536 to 0.842; p = 0.03) were predictive of MVO. Combined IMR and CFRthermo increased the area under the curve for MVO to 0.941.

CONCLUSIONS: In patients who underwent primary PCI for STEMI, an increased IMR has an independent predictive value for MVO detection, and combined high IMR and low CFRthermo are highly predictive of MVO. These indexes could be used to further risk-stratify patients and guide regional and systemic therapies.