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Updated: May 3, 2026
Non-invasive Assessment of Microvascular and Endothelial Function
Published on: January 29, 2013
Core Laboratory Comparison of Angiography-Derived Indexes of Microvascular Resistance vs Pressure-Wire IMR and
Tsung-Ying Tsai1, Ali Aldujeli2, Danielle C J Keulards3
1Cardiovascular Center, Taichung Veterans General Hospital, Taichung, Taiwan; CORRIB Research Centre for Advanced Imaging and Core Lab, University of Galway, Galway, Ireland.
Background:
Coronary microvascular dysfunction should be assessed in patients with angina and nonobstructive coronary arteries. However, established indexes, such as the pressure wire-derived index of microvascular resistance (PW-IMR) and continuous thermodilution-derived absolute hyperemic microvascular resistance (Rmicro) remain underused, driving development of the wire-free angiography-derived index of microvascular resistance (angio-IMR).
Objectives:
The aim of this study was to conduct a core laboratory comparison of 5 angio-IMR methods.
Methods:
Five angio-IMR methods derived from 3 software platforms (QAngio XA 3D, FlashAngio, and AngioPlus Core) were compared against PW-IMR in 270 patients (274 vessels) and Rmicro in 42 patients (109 vessels) in a blinded fashion. Diagnostic performance was assessed on a per-vessel basis using receiver-operating characteristic (ROC) curves, Bland-Altman plots, and confusion matrices.
Results:
The median PW-IMR was 19.02 (Q1-Q3: 12.79-28.08), with 81 of 274 vessels (29.6%) having PW-IMR ≥25. The median Rmicro was 387.50 Wood units (WU) (Q1-Q3: 312.00-501.00 WU), with 33 of 109 vessels (30.3%) having Rmicro ≥475 WU. The correlations among angio-IMR, PW-IMR, and Rmicro were poor across all methods. Three of the 5 methodologies overestimated PW-IMR (mean bias -20.72 to -26.36), with all exhibiting large random errors. ROC analysis using angio-IMR for discriminating PW-IMR ≥25 showed areas under the ROC curve ranging from 0.530 to 0.576 (P > 0.05 for all), while 3 methods (methods A, B, and D) showed significantly better areas under the ROC curve to discriminate Rmicro ≥ 475 WU. When using the prespecified angio-IMR ≥25 threshold, only method E demonstrated acceptable accuracies of 61.4% and 62.0% to identify PW-IMR ≥25 and Rmicro ≥475 WU, respectively.
Conclusions:
All 5 angio-IMR methods demonstrated poor diagnostic accuracy compared with PW-IMR and Rmicro, highlighting significant limitations in their clinical utility.
Insights
New angiography-derived index of microvascular resistance (Angio-IMR) methods show poor accuracy for diagnosing coronary microvascular dysfunction. These wire-free techniques require further development before clinical use.
Area of Science:
- Cardiology
- Medical Imaging
- Vascular Biology
Background:
- Coronary microvascular dysfunction (CMD) is crucial in patients with angina and non-obstructive coronary artery disease.
- Established indices like pressure-wire-derived index of microvascular resistance (PW-IMR) and continuous thermodilution-derived absolute hyperemic microvascular resistance (Rmicro) are underutilized.
- Development of wire-free angiography-derived IMR (Angio-IMR) aims to improve CMD assessment.
Purpose of the Study:
- To perform a core lab comparison of five Angio-IMR methods.
- To evaluate the diagnostic performance of Angio-IMR against established indices (PW-IMR and Rmicro).
Main Methods:
- Five Angio-IMR methods from three software platforms were compared against PW-IMR (274 vessels) and Rmicro (109 vessels).
- Comparisons were conducted in a blinded fashion using receiver-operating characteristic (ROC) curves, Bland-Altman plots, and confusion matrices.
- Diagnostic performance was assessed on a per-vessel basis.
Main Results:
- Correlations between Angio-IMR methods, PW-IMR, and Rmicro were poor across all tested methods.
- Three methods overestimated PW-IMR with significant random errors.
- ROC analysis showed limited ability of Angio-IMR to discriminate between normal and abnormal microvascular resistance, with only one method showing acceptable accuracy.
Conclusions:
- All five Angio-IMR methods exhibited poor diagnostic accuracy when compared to PW-IMR and Rmicro.
- Current Angio-IMR methods have significant limitations for clinical utility in diagnosing CMD.
- Further research and development are needed to improve the accuracy and reliability of wire-free Angio-IMR techniques.
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