Abstract
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.
The index of microvascular resistance correlates with microvascular pathology and is a diagnostic test of myocardial reperfusion in patients with acute ST-elevation myocardial infarction.