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

Abstract

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. IMR (<i>n</i> = 288) and CFR (<i>n</i> = 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 (<i>n</i> = 281) and 6 months after STEMI (<i>n</i> = 264). All-cause death or first heart failure hospitalization was independently adjudicated (median follow-up 845 days). 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], <i>P</i> < 0.001; CFR: 1.7 [1.4-2.5] vs. 1.5 [1.1-1.8] vs. 1.4 [1.0-1.8], <i>P</i> < 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]; <i>P</i> = 0.036), whereas CFR was not (<i>P</i> = 0.160). IMR (5 units) was a multivariable associate of all-cause death or heart failure hospitalization (<i>n</i> = 30 events; hazard ratio [95% CI], 1.09 [1.04, 1.14]; <i>P</i> < 0.001), whereas CFR (<i>P</i> = 0.124) and thrombolysis in myocardial infarction blush grade (<i>P</i> = 0.613) were not. IMR had similar prognostic value for these outcomes as <50% ST-segment resolution on the ECG. IMR is more closely associated with microvascular pathology, left ventricular remodeling, and health outcomes than the angiogram or CFR. NCT02072850. 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.