Index of Microcirculatory Resistance as a Tool to Characterize Microvascular Obstruction and to Predict Infarct Size Regression in Patients With STEMI Undergoing Primary PCI

JACC Cardiovasc Imaging. 2019 May;12(5):837-848. doi: 10.1016/j.jcmg.2018.02.018. Epub 2018 Apr 18.


Objectives: This study aimed to compare the value of the index of microcirculatory resistance (IMR) and microvascular obstruction (MVO) measured by cardiac magnetic resonance (CMR) in patients treated for and recovering from ST-segment elevation myocardial infarction.

Background: IMR can identify patients with microvascular dysfunction acutely after primary percutaneous coronary intervention (pPCI), and a threshold of >40 has been shown to be associated with an adverse clinical outcome. Similarly, MVO is recognized as an adverse feature in patients with ST-segment elevation myocardial infarction. Even though both IMR and MVO reflect coronary microvascular status, the interaction between these 2 parameters is uncertain.

Methods: A total of 110 patients treated with pPCI were included, and IMR was measured immediately at completion of pPCI. Infarct size (IS) as a percentage of left ventricular mass was quantified at 48 h (38.4 ± 12.0 h) and 6 months (194.0 ± 20.0 days) using CMR. MVO was identified and quantified at 48 h by CMR.

Results: Overall, a discordance between IMR and MVO was observed in 36.7% of cases, with 31 patients having MVO and IMR ≤40. Compared with patients with MVO and IMR ≤40, patients with both MVO and IMR >40 had an 11.9-fold increased risk of final IS >25% at 6 months (p = 0.001). Patients with MVO and IMR ≤40 had a significantly smaller IS at 6 months (p = 0.001), with significant regression in IS over time (34.4% [interquartile range (IQR): 27.3% to 41.0%] vs. 22.3% [IQR: 16.0% to 30.0%]; p = 0.001).

Conclusions: Discordant prognostic information was obtained from IMR and MVO in nearly one-third of cases; however, IMR can be helpful in grading the degree and severity of MVO.

Keywords: ST-segment elevation myocardial infarction; index of microcirculatory resistance; microvascular obstruction; primary percutaneous coronary intervention.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Coronary Circulation*
  • Female
  • Humans
  • Magnetic Resonance Imaging, Cine*
  • Male
  • Microcirculation*
  • Middle Aged
  • Myocardial Reperfusion Injury / diagnostic imaging*
  • Myocardial Reperfusion Injury / etiology
  • Myocardial Reperfusion Injury / pathology
  • Myocardial Reperfusion Injury / physiopathology
  • Myocardium / pathology*
  • Percutaneous Coronary Intervention / adverse effects*
  • Predictive Value of Tests
  • Retrospective Studies
  • Risk Factors
  • ST Elevation Myocardial Infarction / diagnostic imaging
  • ST Elevation Myocardial Infarction / physiopathology
  • ST Elevation Myocardial Infarction / therapy*
  • Severity of Illness Index
  • Treatment Outcome