Microvascular resistance of the culprit coronary artery in acute ST-elevation myocardial infarction.

BACKGROUND: Failed myocardial reperfusion is common and prognostically important after acute ST-elevation myocardial infarction (STEMI). The purpose of this study was to investigate coronary flow reserve (CFR), a measure of vasodilator capacity, and the index of microvascular resistance (IMR; mmHg × s) in the culprit artery of STEMI survivors. METHODS: IMR (n = 288) and CFR (n = 283; mean age [SD], 60 [12] years) were measured acutely using guide wire-based thermodilution. Cardiac MRI disclosed left ventricular pathology, function, and volumes at 2 days (n = 281) and 6 months after STEMI (n = 264). All-cause death or first heart failure hospitalization was independently adjudicated (median follow-up 845 days). RESULTS: Myocardial hemorrhage and microvascular obstruction occurred in 89 (42%) and 114 (54%) patients with evaluable T2*-MRI maps. IMR and CFR were associated with microvascular pathology (none vs. microvascular obstruction only vs. microvascular obstruction and myocardial hemorrhage) (median [interquartile range], IMR: 17 [12.0-33.0] vs. 17 [13.0-39.0] vs. 37 [21.0-63.0], P < 0.001; CFR: 1.7 [1.4-2.5] vs. 1.5 [1.1-1.8] vs. 1.4 [1.0-1.8], P < 0.001), whereas thrombolysis in myocardial infarction blush grade was not. IMR was a multivariable associate of changes in left ventricular end-diastolic volume (regression coefficient [95% CI] 0.13 [0.01, 0.24]; P = 0.036), whereas CFR was not (P = 0.160). IMR (5 units) was a multivariable associate of all-cause death or heart failure hospitalization (n = 30 events; hazard ratio [95% CI], 1.09 [1.04, 1.14]; P < 0.001), whereas CFR (P = 0.124) and thrombolysis in myocardial infarction blush grade (P = 0.613) were not. IMR had similar prognostic value for these outcomes as <50% ST-segment resolution on the ECG. CONCLUSIONS: IMR is more closely associated with microvascular pathology, left ventricular remodeling, and health outcomes than the angiogram or CFR. TRIAL REGISTRATION: NCT02072850. FUNDING: A British Heart Foundation Project Grant (PG/11/2/28474), the National Health Service, the Chief Scientist Office, a Scottish Funding Council Senior Fellowship, a British Heart Foundation Intermediate Fellowship (FS/12/62/29889), and a nonfinancial research agreement with Siemens Healthcare.

Assessment of Fractional Flow Reserve in Patients With Recent Non-ST-Segment-Elevation Myocardial Infarction: Comparative Study With 3-T Stress Perfusion Cardiac Magnetic Resonance Imaging.

BACKGROUND: The use of fractional flow reserve (FFR) in acute coronary syndromes is controversial. The British Heart Foundation Fractional Flow Reserve Versus Angiography in Guiding Management to Optimize Outcomes in Non-ST-Elevation Myocardial Infarction (FAMOUS-NSTEMI) study (NCT01764334) has recently demonstrated the safety and feasibility of FFR measurement in patients with non-ST-segment-elevation myocardial infarction. We report the findings of the cardiac magnetic resonance (CMR) substudy to assess the diagnostic accuracy of FFR compared with 3.0-T stress CMR perfusion. METHODS AND RESULTS: One hundred six patients with non-ST-segment-elevation myocardial infarction who had been referred for early invasive management were included from 2 centers. FFR was measured in all major patent epicardial coronary arteries with a visual stenosis estimated at ≥30%, and if percutaneous coronary intervention was performed, an FFR assessment was repeated. Myocardial perfusion was assessed with stress perfusion CMR at 3 T. The mean age was 56.7±9.8 years; 82.6% were men. Mean time from FFR evaluation to CMR was 6.1±3.1 days. The mean±SD left ventricular ejection fraction was 58.2±9.1%. Mean infarct size was 5.4±7.1%, and mean troponin concentration was 5.2±9.2 µg/L. There were 34 fixed and 160 inducible perfusion defects. There was a negative correlation between the number of segments with a perfusion abnormality and FFR (r=-0.77; P<0.0001). The overall sensitivity, specificity, positive predictive value, and negative predictive value for an FFR of ≤0.8 were 91.4%, 92.2%, 76%, and 97%, respectively. Diagnostic accuracy was 92%. The positive and negative predictive values of FFR for flow-limiting coronary artery disease (FFR≤0.8) in patients with non-ST-segment-elevation myocardial infarction (n=21) who underwent perfusion CMR before invasive angiography were 92% and 93%, respectively. Receiver operating characteristic analysis indicated that the optimal cutoff value of FFR for demonstrating reversible ischemia on CMR was ≤0.805 (area under the receiver operating characteristic curve, 0.94 [0.9-0.99]; P<0.0001). CONCLUSIONS: FFR in patients with recent non-ST-segment-elevation myocardial infarction showed high concordance with myocardial perfusion in matched territories as revealed by 3.0-T stress perfusion CMR. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT02073422.