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Updated: Jul 15, 2026
Non-invasive Assessment of Microvascular and Endothelial Function
Published on: January 29, 2013
Invasive minimal Microvascular Resistance Is a New Index to Assess Microcirculatory Function Independent of
Guus A de Waard1, Sukhjinder S Nijjer2, Martijn A van Lavieren3
1VU University Medical Center, Amsterdam, The Netherlands.
Insights
Minimal microvascular resistance (mMR) is a new index for assessing coronary microcirculatory dysfunction. Unlike other measures, mMR is not affected by coronary artery disease (CAD), offering a more reliable assessment of microvascular function.
Area of Science:
- Cardiology
- Vascular Physiology
- Diagnostic Imaging
Background:
- Coronary microcirculatory dysfunction is linked to poor cardiovascular outcomes.
- Current invasive assessments like coronary flow reserve (CFR) and hyperemic microvascular resistance (HMR) can be influenced by coronary artery disease (CAD).
- There is a need for a reliable microvascular dysfunction index unaffected by obstructive CAD.
Purpose of the Study:
- To introduce minimal microvascular resistance (mMR) as a novel index for assessing coronary microcirculatory dysfunction.
- To determine if mMR is influenced by the presence of obstructive CAD.
- To compare mMR with established indices (CFR, HMR) in relation to CAD severity.
Main Methods:
- Simultaneous intracoronary Doppler flow velocity and pressure measurements were obtained from 482 individuals.
- Minimal microvascular resistance (mMR) was calculated as the ratio of distal coronary pressure to flow velocity during the hyperemic wave-free period.
- Paired analysis (Cohort 1) compared mMR, CFR, and HMR in vessels with and without CAD; validation (Cohort 2) assessed associations with fractional flow reserve (FFR).
Main Results:
- Coronary flow reserve (CFR) was lower and hyperemic microvascular resistance (HMR) was higher in vessels with CAD compared to those without.
- Minimal microvascular resistance (mMR) showed no significant difference between vessels with and without CAD (P=0.90).
- Unlike CFR and HMR, mMR demonstrated no association with fractional flow reserve (FFR) across different strata.
Conclusions:
- Minimal microvascular resistance (mMR) is a novel index for evaluating microcirculatory dysfunction.
- The presence of obstructive coronary artery disease does not alter mMR measurements.
- mMR offers a potential advantage over CFR and HMR due to its independence from obstructive CAD.
Background:
Coronary microcirculatory dysfunction portends a poor cardiovascular outcome. Invasive assessment of microcirculatory dysfunction by coronary flow reserve (CFR) and hyperemic microvascular resistance (HMR) is affected by coronary artery disease (CAD). In this study we propose minimal microvascular resistance (mMR) as a new measure of microcirculatory dysfunction and aim to determine whether mMR is influenced by CAD.
Methods And Results:
We obtained 482 simultaneous measurements of intracoronary Doppler flow velocity and pressure. The mMR is defined as the ratio between distal coronary pressure and flow velocity during the hyperemic wave-free period. Measurements were divided into 2 cohorts. Cohort 1 was a paired analysis involving 81 pairs with a vessel with and without CAD to investigate whether HMR, CFR, and mMR are modulated by CAD. CFR was lower, and HMR was higher, in vessels with CAD than in vessels without CAD: 2.12±0.79 versus 2.56±0.63 mm Hg·cm-1·s, P<0.001, and 2.61±1.22 versus 2.31±0.89 mm Hg·cm-1·s, P=0.04, respectively. mMR was equal in vessels with and without CAD: 1.54±0.77 versus 1.53±0.57 mm Hg·cm-1·s, P=0.90. Differences for CFR occurred when FFR was 0.60 to 0.80 or ≤0.60 but not when FFR ≥0.80. For HMR, the difference occurred only when FFR ≤0.60. For mMR, no difference was observed in any FFR stratum. Cohort 2 was used for validation and showed significant relationships for CFR and HMR with FFR: Pearson r=0.488, P<0.001 and -0.159, P=0.03, respectively; mMR had no association with FFR: Pearson r=0.055; P=0.32.
Conclusions:
mMR is a novel index to assess microcirculatory dysfunction and is not modified by the presence of obstructive CAD.
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