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Peer-reviewedCC BY 4.0Frontiers in Cardiovascular Medicine

Microvascular resistance reserve: insights into discordant resting and hyperemic epicardial coronary physiology

  • Aswin Babu1,2
  • Isobelle Goldrick1
  • Billy Broadbent2
  • Rania Faeq2
  • Charley Budgeon2
  • Roopa Krishnamoorthy1
  • Primero Ng1
  • Cara Barnes1
  • Dipen Sankhesara1
  • Avadhesh Saraswat1
  • Imran Shiekh1
  • James Marangou1
5 more authors
  • Richard Alcock1
  • Rachel Orme1
  • Carl Schultz1,2
  • Graham S Hillis1,2
  • Jon Spiro1,2
  1. 1Department of Cardiology, Royal Perth Hospital, Perth, WA, Australia.
  2. 2School of Medicine, University of Western Australia, Perth, WA, Australia.
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Abstract

Introduction: Discordance between resting and hyperemic epicardial physiology is commonbut mechanistically unclear. Microvascular resistance reserve (MRR), a novelindex of vasodilatory capacity, may provide insight. We aimed to characterizethe prevalence and microvascular substrate of FFR/RFR discordance, andwhether MRR is independently associated with discordant phenotypes.

Methods: We retrospectively analyzed 891 vessels from 723 consecutive patients with paired resting full-cycle ratio (RFR) and fractional flow reserve (FFR) measurements (June 2018–October 2024). Vessels were categorized as concordant or discordant. An operator-selected subset of 210 underwent coronary flow reserve (CFR), index of microvascular resistance (IMR), and MRR assessment. Multivariable logistic regression identified predictors of each discordant phenotype (FFR−/RFR+ and FFR+/RFR−).

Results: Discordance was present in 195 vessels (22%); 121 (13.6%) FFR−/RFR+ and 74 (8.3%) FFR+/RFR−. Discordance was more common in the LAD (25% vs. 17%, OR 1.68, 95% CI 1.20–2.36, p = 0.003), driven predominantly by the FFR−/RFR+ phenotype (OR 2.43, 95% CI 1.56–3.78, p < 0.001). In the microvascular subset ( n = 210), reduced CFR (OR 0.77, 95% CI 0.59–0.97, p = 0.039) and reduced MRR (OR 0.81, 95% CI 0.65–0.97, p = 0.037) were independently associated with the FFR−/RFR+ phenotype, while neither predicted the FFR+/RFR− phenotype. However, among 45 discordant vessels with microvascular data, MRR provided greater discrimination than CFR (AUC 0.712, 95% CI 0.539–0.884 vs. 0.608, 95% CI 0.434–0.783, p = 0.018).

Discussion: These exploratory, hypothesis-generating findings suggest that impaired microvascular vasodilatory reserve, expressed predominantly as elevated resting flow, may contribute mechanistically to the FFR−/RFR+ phenotype.

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Cite

BibTeXRIS
BibTeX
@article{babu2026microvascular,
  title = {{Microvascular resistance reserve: insights into discordant resting and hyperemic epicardial coronary physiology}},
  author = {Aswin Babu and Isobelle Goldrick and Billy Broadbent and Rania Faeq and Charley Budgeon and Roopa Krishnamoorthy and Primero Ng and Cara Barnes and Dipen Sankhesara and Avadhesh Saraswat and Imran Shiekh and James Marangou and Richard Alcock and Rachel Orme and Carl Schultz and Graham S Hillis and Jon Spiro},
  journal = {Frontiers in Cardiovascular Medicine},
  year = {2026},
  month = oct,
  doi = {10.3389/fcvm.2026.1929694},
  url = {https://www.frontiersin.org/articles/10.3389/fcvm.2026.1929694/full},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Microvascular resistance reserve: insights into discordant resting and hyperemic epicardial coronary physiology
AU  - Aswin Babu
AU  - Isobelle Goldrick
AU  - Billy Broadbent
AU  - Rania Faeq
AU  - Charley Budgeon
AU  - Roopa Krishnamoorthy
AU  - Primero Ng
AU  - Cara Barnes
AU  - Dipen Sankhesara
AU  - Avadhesh Saraswat
AU  - Imran Shiekh
AU  - James Marangou
AU  - Richard Alcock
AU  - Rachel Orme
AU  - Carl Schultz
AU  - Graham S Hillis
AU  - Jon Spiro
PY  - 2026
DA  - 2026/10/14
JO  - Frontiers in Cardiovascular Medicine
DO  - 10.3389/fcvm.2026.1929694
UR  - https://www.frontiersin.org/articles/10.3389/fcvm.2026.1929694/full
AB  - Introduction: Discordance between resting and hyperemic epicardial physiology is commonbut mechanistically unclear. Microvascular resistance reserve (MRR), a novelindex of vasodilatory capacity, may provide insight. We aimed to characterizethe prevalence and microvascular substrate of FFR/RFR discordance, andwhether MRR is independently associated with discordant phenotypes.  Methods: We retrospectively analyzed 891 vessels from 723 consecutive patients with paired resting full-cycle ratio (RFR) and fractional flow reserve (FFR) measurements (June 2018–October 2024). Vessels were categorized as concordant or discordant. An operator-selected subset of 210 underwent coronary flow reserve (CFR), index of microvascular resistance (IMR), and MRR assessment. Multivariable logistic regression identified predictors of each discordant phenotype (FFR−/RFR+ and FFR+/RFR−).  Results: Discordance was present in 195 vessels (22%); 121 (13.6%) FFR−/RFR+ and 74 (8.3%) FFR+/RFR−. Discordance was more common in the LAD (25% vs. 17%, OR 1.68, 95% CI 1.20–2.36, p = 0.003), driven predominantly by the FFR−/RFR+ phenotype (OR 2.43, 95% CI 1.56–3.78, p < 0.001). In the microvascular subset ( n = 210), reduced CFR (OR 0.77, 95% CI 0.59–0.97, p = 0.039) and reduced MRR (OR 0.81, 95% CI 0.65–0.97, p = 0.037) were independently associated with the FFR−/RFR+ phenotype, while neither predicted the FFR+/RFR− phenotype. However, among 45 discordant vessels with microvascular data, MRR provided greater discrimination than CFR (AUC 0.712, 95% CI 0.539–0.884 vs. 0.608, 95% CI 0.434–0.783, p = 0.018).  Discussion: These exploratory, hypothesis-generating findings suggest that impaired microvascular vasodilatory reserve, expressed predominantly as elevated resting flow, may contribute mechanistically to the FFR−/RFR+ phenotype.
SN  - 2297-055X
ER  -