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Comparative Prognostic Utility of Indexes of Microvascular Function Alone or in Combination in Patients With an Acute
David Carrick1, Caroline Haig1, Nadeem Ahmed1
1From BHF Glasgow Cardiovascular Research Centre, Institute of Cardiovascular and Medical Sciences (D.C., N.A., J.C., V.T.Y.M., M.M., M.C.P., I.M., A.R., K.G.O., C.B.), and Robertson Centre for Biostatistics (C.H., I.F.), University of Glasgow, Glasgow, UK; and West of Scotland Heart and Lung Centre, Golden Jubilee National Hospital, Clydebank, UK (D.C., N.A., J.C., V.T.Y.M., M.M., M.C.P., H.E., M.L., S.H.., S.W., A.D., A.M., I.M., K.G.O., C.B.).
Insights
Index of microvascular resistance (IMR) >40 is a strong predictor of poor outcomes after ST-segment-elevation myocardial infarction, independent of infarct size. This measure offers superior risk stratification compared to standard clinical indicators of reperfusion efficacy.
Area of Science:
- Cardiology
- Vascular Biology
- Medical Diagnostics
Background:
- Primary percutaneous coronary intervention (PCI) for ST-segment-elevation myocardial infarction (STEMI) aims to restore blood flow but often fails to detect inadequate reperfusion in up to 50% of patients.
- The index of microvascular resistance (IMR) is an emerging invasive metric for assessing coronary microvascular function.
Purpose of the Study:
- To evaluate the pathological and prognostic significance of an IMR >40, with or without a coronary flow reserve (CFR) ≤2.0, in the culprit artery post-emergency PCI for STEMI.
Main Methods:
- Prospective enrollment of STEMI patients undergoing emergency PCI.
- Categorization based on IMR (≤40 or >40) and CFR (≤2.0 or >2.0).
- Cardiac MRI at 2 days and 6 months post-MI; primary outcome was all-cause death or heart failure hospitalization (median follow-up 845 days).
Main Results:
- In 283 STEMI patients, an IMR >40 was associated with myocardial hemorrhage and microvascular obstruction, independent of reperfusion time or blush grade.
- An IMR >40 independently predicted adverse changes in left ventricular ejection fraction and end-diastolic volume at 6 months.
- An IMR >40 significantly predicted all-cause death or heart failure (OR 4.36, P<0.001); combining it with CFR≤2.0 did not improve prognostic value.
Conclusions:
- An IMR >40 is a significant independent predictor of adverse left ventricular remodeling and clinical outcomes post-STEMI.
- IMR demonstrates superior clinical utility for risk stratification in failed myocardial reperfusion compared to standard measures like ischemic time, ST-segment resolution, or CFR.
- IMR may serve as a reference standard for assessing failed myocardial reperfusion efficacy.
Background:
Primary percutaneous coronary intervention 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 IMR>40, alone or in combination with a coronary flow reserve (CFR≤2.0), in the culprit artery after emergency percutaneous coronary intervention for acute ST-segment-elevation myocardial infarction.
Methods:
Patients with acute ST-segment-elevation myocardial infarction were prospectively enrolled during emergency percutaneous coronary intervention and categorized according to IMR (≤40 or >40) and CFR (≤2.0 or >2.0). Cardiac magnetic resonance imaging was acquired 2 days and 6 months after myocardial infarction. All-cause death or first heart failure hospitalization was a prespecified outcome (median follow-up, 845 days).
Results:
IMR and CFR were measured in the culprit artery at the end of percutaneous coronary intervention in 283 patients with ST-segment-elevation myocardial infarction (mean±SD age, 60±12 years; 73% male). The median IMR and CFR were 25 (interquartile range, 15-48) and 1.6 (interquartile range, 1.1-2.1), respectively. An IMR>40 was a multivariable associate of myocardial hemorrhage (odds ratio, 2.10; 95% confidence interval, 1.03-4.27; P=0.042). An IMR>40 was closely associated with microvascular obstruction. Symptom-to-reperfusion time, TIMI (Thrombolysis in Myocardial Infarction) 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 left ventricular ejection fraction (coefficient, -2.12; 95% confidence interval, -4.02 to -0.23; P=0.028) and left ventricular end-diastolic volume (coefficient, 7.85; 95% confidence interval, 0.41-15.29; P=0.039) at 6 months independently of infarct size. An IMR>40 (odds ratio, 4.36; 95% confidence interval, 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 and CFR≤2.0 did not have incremental prognostic value.
Conclusions:
An IMR>40 is a multivariable associate of left ventricular and clinical outcomes after ST-segment-elevation myocardial infarction independently of the infarction size. Compared with standard clinical measures of the efficacy of myocardial reperfusion, including the ischemic time, ST-segment elevation, angiographic blush grade, and CFR, IMR has superior clinical value for risk stratification and may be considered a reference test for failed myocardial reperfusion.
Clinical Trial Registration:
URL: https//www.clinicaltrials.gov. Unique identifier: NCT02072850.
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