Comparative Prognostic Utility of Indices of Microvascular Function Alone or in Combination in Patients with an Acute ST-Segment Elevation Myocardial Infarction
Background—Primary percutaneous coronary intervention (PCI) is frequently successful at restoring coronary artery blood flow in patients with acute ST-segment elevation myocardial infarction, however, failed myocardial reperfusion commonly passes undetected in up to half of these patients. The index of microvascular resistance (IMR) is a novel invasive measure of coronary microvascular function. We aimed to investigate the pathological and prognostic significance of an index of microvascular resistance (IMR>40), alone or in combination with a coronary flow reserve (CFR≤2.0), in the culprit artery after emergency PCI for acute STEMI.
Methods—Patients with acute STEMI were prospectively enrolled during emergency PCI, and categorized according to IMR (≤40 or >40) and CFR (≤2.0 or >2.0). Cardiac MRI was acquired 2 days and 6 months post-MI. All-cause death or first heart failure hospitalization was a pre-specified outcome (median follow-up duration 845 days).
Results—IMR and CFR were measured in the culprit artery at the end of PCI in 283 STEMI patients (mean age 60 (12) years, 73% male). The median [interquartile range] IMR and CFR were 25 [15-48] and 1.6 [1.1-2.1], respectively. An IMR>40 was a multivariable associate of myocardial hemorrhage (odds ratio (OR) (95% confidence interval (CI)) 2.10 (1.03, 4.27); p=0.042. An IMR>40 was closely associated with microvascular obstruction. Symptom to reperfusion time, TIMI blush grade, and no (≤30%) ST segment resolution, were not associated with these pathologies. An IMR>40 was a multivariable associate of the changes in LV ejection fraction (coefficient (95% CI) (-2.12 (-4.02, -0.23); p=0.028) and LV end-diastolic volume (7.85 (0.41, 15.29); p=0.039) at 6 months, independent of infarct size. An IMR>40 (odds ratio 4.36 (95% CI 2.10, 9.06); p<0.001) was a multivariable associate of all-cause death or heart failure. Compared with an IMR>40, the combination of IMR>40 with CFR≤2.0 did not have incremental prognostic value.
Conclusions—An IMR>40 is a multivariable associate of LV and clinical outcomes post-STEMI, independent of the size of infarction. Compared with standard clinical measures of the efficacy of myocardial reperfusion, including the ischemic time, ST-segment elevation, the angiographic blush grade and CFR, IMR has superior clinical value for risk stratification and may be considered as a reference test for failed myocardial reperfusion.
- myocardial infarction
- magnetic resonance imaging
- microvascular dysfunction
- Received March 21, 2016.
- Revision received August 16, 2016.
- Accepted October 5, 2016.
Circulation is published on behalf of the American Heart Association, Inc., by Wolters Kluwer. This is an open access article under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0/), which permits use, distribution, and reproduction in any medium, provided that the original work is properly cited.