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Prognostic Value of Microvascular Resistance Reserve in Coronary Artery Disease: A Systematic Review and
Emanuele Gallinoro1, Bernard De Bruyne2, Nico Pijls3
1Cardiology Unit, Sant'Andrea University Hospital, Rome, Italy.
Insights
Microvascular resistance reserve (MRR) predicts cardiovascular outcomes in coronary artery disease (CAD). Higher MRR indicates lower risk, with a threshold of 3 offering optimal prognostic balance for risk stratification.
Area of Science:
- Cardiology
- Vascular Biology
- Diagnostic Imaging
Background:
- Microvascular resistance reserve (MRR) assesses coronary microvascular function, independent of epicardial disease.
- The prognostic value of MRR in coronary artery disease (CAD) requires further clarification.
Purpose of the Study:
- To evaluate the association between MRR and adverse cardiovascular outcomes in patients with various CAD presentations.
- To determine the prognostic significance of MRR across different CAD scenarios.
Main Methods:
- A systematic review and meta-analysis adhering to PRISMA guidelines.
- Searched MEDLINE and Embase (Jan 2019-Jan 2025) for prospective studies on MRR and major adverse cardiovascular events (MACE).
- Pooled hazard ratios (HRs) using a random-effects model, assessing heterogeneity with I² statistic.
Main Results:
- Included 5 studies (3,186 participants); higher MRR correlated with reduced adverse event risk (HR: 0.75 per unit increase).
- Low MRR demonstrated a >2-fold increased risk for MACE (HR: 2.39).
- Prognostic impact was greater in ST-elevation myocardial infarction (HR: 0.46) vs. stable CAD (HR: 0.86); MRR ≥ 3 showed optimal sensitivity for risk stratification.
Conclusions:
- MRR is a strong, independent predictor of cardiovascular outcomes in both acute and chronic CAD.
- Prognostic value is particularly significant in acute coronary syndromes.
- An MRR threshold of 3 is recommended for optimal risk stratification in invasive assessments.
Background:
Microvascular resistance reserve (MRR) is a novel index for evaluating coronary microvascular function independently of epicardial disease. Its prognostic significance in coronary artery disease (CAD) remains uncertain.
Objectives:
The aim of this study was to assess the association between MRR and adverse cardiovascular outcomes across various CAD presentations.
Methods:
A systematic review and meta-analysis was conducted according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. MEDLINE and Embase were searched from January 2019 to January 2025 for prospective studies reporting HRs for major adverse cardiovascular events in relation to MRR. Risk for bias was assessed using the Quality in Prognosis Studies tool. Pooled HRs were calculated using a random-effects model; heterogeneity was evaluated using the I2 statistic.
Results:
Five studies (n = 3,186) were included. Higher MRR was significantly associated with lower risk for adverse events (HR per unit increase: 0.75; 95% CI: 0.64-0.88; I2 = 80.9%). When dichotomized, low MRR conferred a more than 2-fold increased risk for major adverse cardiovascular events (HR: 2.39; 95% CI: 1.66-3.43). Subgroup analysis showed a stronger prognostic effect for ST-segment elevation myocardial infarction (HR: 0.46) vs stable CAD (HR: 0.86; P for interaction < 0.0001). Threshold analysis identified MRR ≥ 3 as optimal for sensitivity (58.9%) and rule-out performance, while lower thresholds improved specificity.
Conclusions:
MRR is a robust, independent predictor of cardiovascular outcomes of both acute and chronic CAD. Its prognostic impact is particularly pronounced for acute coronary syndrome. A threshold of 3 provides the best prognostic balance, supporting its integration into invasive physiological assessment for risk stratification.
