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Updated: Feb 2, 2026
Acute Myocardial Infarction in Rats
Published on: February 16, 2011
Microvascular dysfunction determines infarct characteristics in patients with reperfused ST-segment elevation
Elisa McAlindon1,2,3, Maria Pufulete2, Jessica Harris2
1Department of Cardiology, Bristol Heart Institute, University Hospitals Bristol NHS Trust, Bristol, United Kingdom.
Background:
In patients with reperfused ST-elevation myocardial infarction (STEMI) both invasive and non-invasive assessments of microvascular dysfunction, the index of microcirculatory resistance (IMR), and microvascular obstruction (MVO) by cardiovascular magnetic resonance (CMR), independently predict poor long-term outcomes.
Aims:
The aims of this study were to investigate whether an invasive parameter (IMR), assessed at the time of primary percutaneous intervention (PPCI), could predict the extent of MVO in proportion to infarct size (MVO index).
Methods:
50 patients presenting with STEMI and TIMI flow ≤ I in the infarct related artery were prospectively recruited to the study, before undergoing PPCI. All patients underwent invasive IMR assessment at maximal hyperaemia using adenosine, and following stent insertion. CMR was performed on day 2 following STEMI, MVO was assessed both on first-pass rest perfusion (early MVO) and in the late gadolinium enhancement (LGE) images (late MVO) along with infarct size. The MVO index was calculated as the ratio of late MVO/infarct size. Differences between IMR quartiles and the MVO index were investigated.
Results:
The median IMR was 38.5 (range 9 to 202). The median size of late MVO was 1.9% LV (range 0 to 21.0% LV). IMR predicted late MVO (p<0.01) and as IMR increased, the MVO index increased (r = 0.70, [95% CI 0.53, 0.82], p<0.001). An IMR cut-off of 40 significantly predicted the presence of late MVO on CMR (p<0.001).
Conclusion:
IMR measured at the time of PPCI in acutely reperfused STEMI is associated with the presence and severity of infarct damage as measured by the MVO index.
Trial Registration:
The Microcirculation in Acute Myocardial Infarction (MICRO-AMI). Clinicaltrials.gov NCT01552564. Registered 9th March 2012.
Insights
Index of microcirculatory resistance (IMR) measured during primary percutaneous intervention predicts microvascular obstruction (MVO) and infarct size in ST-elevation myocardial infarction (STEMI) patients, aiding in assessing long-term outcomes.
Area of Science:
- Cardiology
- Interventional Cardiology
- Cardiovascular Imaging
Background:
- Microvascular dysfunction, assessed by index of microcirculatory resistance (IMR) and microvascular obstruction (MVO) via cardiovascular magnetic resonance (CMR), predicts poor outcomes in reperfused ST-elevation myocardial infarction (STEMI).
- Assessing microvascular function is crucial for managing STEMI patients.
Purpose of the Study:
- To determine if invasive IMR, measured during primary percutaneous intervention (PPCI), can predict the extent of MVO relative to infarct size (MVO index).
Main Methods:
- 50 STEMI patients undergoing PPCI had invasive IMR assessed. Cardiovascular magnetic resonance (CMR) was used on day 2 to evaluate MVO (early and late) and infarct size.
- The MVO index was calculated as the ratio of late MVO to infarct size. IMR quartiles were analyzed against the MVO index.
Main Results:
- Median IMR was 38.5. Median late MVO was 1.9% LV. IMR significantly predicted late MVO (p<0.01).
- A higher IMR correlated with an increased MVO index (r = 0.70, p<0.001). An IMR cut-off of 40 predicted late MVO (p<0.001).
Conclusions:
- IMR measurement during PPCI in STEMI is linked to the presence and severity of infarct damage, as indicated by the MVO index.
- IMR serves as a valuable invasive marker for microvascular impairment post-STEMI.
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