Invasive assessment of coronary microvascular dysfunction and its association with clinical outcomes in patients with acute coronary syndrome: a meta-analysis

Background The index of microcirculatory resistance (IMR) is an invasive physiological marker used to evaluate coronary microvascular dysfunction. Growing evidence indicates that IMR may offer prognostic insights beyond traditional epicardial coronary assessments, making it a valuable tool for risk stratification. However, the relationship between IMR and clinical outcomes in patients with acute myocardial infarction (AMI) remains incompletely understood. Purpose This study evaluated the prognostic value of IMR, measured invasively using the thermodilution method post PCI, in patients with AMI. Methods We conducted a systematic literature search for studies assessing post-PCI IMR in patients with AMI. We recorded the year of publication, type of AMI, method of IMR assessment,the used cutoffs, patients’ age, sex, cardiovascular risk factors, & follow-up duration.The outcomes of interest were all-cause mortality (ACM), cardiovascular mortality (CVM), hospitalization for HF (HHF), reinfarction (MI), cerebrovascular events (STROKE), revascularization clinically driven revascularization (REVASC) as well as combined endpoints (MACE) at maximal follow-up. We extracted the event rates (or the odds ratios (OR) where available) for those endpoints for the groups with and without abnormal IMR.I2 was chosen as the measure of between-study heterogeneity,with values exceeding 50% being considered significant. Results We identified a total of 680 studies,of which 18 were ultimately selected for data extraction and inclusion in the meta-analysis after screening of title/abstract/full-text. Most studies measured the IMR using a pressure/temperature sensor-tipped wire,while one study utilized a Doppler wire. Cutoffs varied across the studies, with most considering IMR>40 as abnormal. The mean age did not exceed 67 years in either group,with the majority of participants being male. The rates of hypertension, diabetes mellitus & dyslipidemia were broadly similar between the intervention and control groups. According to the meta-analysis results, compared to the normal IMR group, the presence of abnormal IMR was associated with higher rates of the combined endpoints of major adverse cardiovascular events (MACE) (Figure 1), as well as their individual components (Figure 2). Notably, there was no significant difference in STROKE (RR: 1.63, 95% CI: 0.60–4.43, p = 0.13) or REVASC (RR: 2.56, 95% CI: 0.72–9.07, p = 0.17). There was no evidence of between-study heterogeneity or publication bias, as confirmed by funnel plot inspection and Egger’s test.Additionally, the results remained consistent following a sensitivity analysis using the leave-one-out method. Conclusion This meta-analysis suggests that post-PCI IMR is associated with an adverse prognosis in patients with AMI. These findings further support the role of coronary physiology assessment in this high-risk subgroup with the potential of individualizing patient management and improving clinical outcomes.MACEs ACM, CVM, hospitalization for lHF, MI