Higher measurements of the index of microcirculatory resistance (IMR) taken during the acute phase of a myocardial infarction are associated with microvascular obstruction (MVO) as defined by cardiovascular magnetic resonance (CMR) imaging, according to a systematic review and meta-analysis published in BMC Cardiovascular Disorders.
The review, led by Jiao-Ying Song and Jian-Yao Shen with colleagues, set out to test whether acute-phase coronary physiology could complement imaging-based assessment of microvascular injury after a heart attack. The researchers searched PubMed, Embase, Web of Science, the Cochrane Library, ClinicalTrials.gov, and the Chinese Clinical Trial Registry through April 2026.
Fifteen reports were included, predominantly involving patients with ST-segment elevation myocardial infarction who underwent primary percutaneous coronary intervention. Study-level mean differences and 95% confidence intervals were calculated from verifiable group data, and diagnostic accuracy was summarized without pooling.
In the study by Ahn and colleagues, the mean difference in IMR was 22.00 units (95% CI, 12.99–31.01). In Hoole and colleagues, mean differences were 25.60 units (95% CI, 6.36–44.84) for early MVO and 14.90 units (95% CI, −9.46 to 39.26) for late MVO within the same cohort, indicating a more consistent association with early than late MVO in that dataset. No primary pooled mean difference was established in the main analysis.
Two diagnostic datasets comprising 250 participants showed sensitivities of 47.5%–56.1% and specificities of 72.3%–82.4% at an IMR threshold of greater than 40 units. In other words, at this cutoff, specificity exceeded sensitivity, while values at or below 40 units did not exclude MVO.
A supplementary reconstruction of 14 effect estimates, using DerSimonian–Laird random-effects models with leave-one-out analyses and assessment of heterogeneity, yielded a mean difference of 17.69 units (95% CI, 12.65–22.73; I² = 75.2%). Excluding the unverified Scarsini estimate reduced the mean difference to 14.76 units (95% CI, 11.45–18.07; I² = 40.7%), lowering heterogeneity considerably.
The authors conclude that higher acute-phase IMR was associated with CMR-defined MVO after myocardial infarction, and that IMR may complement microvascular injury assessment, but that its clinical utility requires independent validation.
The findings position IMR as a potential physiological adjunct to CMR in characterizing microvascular injury after myocardial infarction, while the modest sensitivity at the 40-unit threshold and the need for independent validation temper any immediate clinical application.
Subject of Research: Association between acute-phase index of microcirculatory resistance and CMR-defined microvascular obstruction after myocardial infarction
Article Title: Index of microcirculatory resistance and cardiovascular magnetic resonance–defined microvascular obstruction after myocardial infarction: a systematic review and meta-analysis
Article References: Song, J.-Y., Sun, M.-F., Chen, L.-Y., & Shen, J.-Y. (2026). Index of microcirculatory resistance and cardiovascular magnetic resonance–defined microvascular obstruction after myocardial infarction: a systematic review and meta-analysis. BMC Cardiovascular Disorders. https://doi.org/10.1186/s12872-026-06882-7
Image Credits: AI Generated
DOI: 10.1186/s12872-026-06882-7
Keywords: index of microcirculatory resistance, microvascular obstruction, cardiovascular magnetic resonance, myocardial infarction, systematic review, meta-analysis, diagnostic accuracy, ST-segment elevation myocardial infarction, coronary physiology, primary percutaneous coronary intervention, Index, microcirculatory
News Source: Ophelia Keating. (October 29, 2026). Higher Microvascular Resistance After Heart Attack Tracks With Imaging-Defined Microvascular Damage. Scienmag.
