Core Laboratory Comparison of Angiography-Derived Indexes of Microvascular Resistance Versus Pressure-wire IMR and Absolute Resistance

Abstract

Background
Coronary microvascular dysfunction should be assessed in patients with angina and non-obstructive coronary artery disease. However, established indices such as the pressure-wire-derived index of microvascular resistance (PW-IMR) and continuous thermodilution–derived absolute hyperemic microvascular resistance (Rmicro) remain underutilized, driving development of the wire-free angiography-derived IMR (Angio-IMR).

Objectives
Core lab comparison of five Angio-IMR methods.

Methods
Five angio-IMR methods derived from three 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 (IQR) PW-IMR was 19.02[12.79–28.08] with 81/274 (29.6%) vessels having a PW-IMR≥25. The median Rmicro was 387.50[312.00–501.00] with 33/109 (30.3%) vessels having an Rmicro≥475 Woods units (WU). The correlations between angio-IMR, PW-IMR, and Rmicro were poor across all methods. Three of the five methodologies overestimated PW-IMR (mean biases -20.72 to -26.36), with all exhibiting large random errors. ROC analysis using angio-IMR for discriminating PW-IMR≥25 showed area under the ROC curve (AUC) ranging from 0.530 to 0.576 (p>0.05 for all), while three methods (A, B, D) showed significantly better AUCs to discriminate Rmicro≥475 WU. When using the pre-specified angio-IMR≥25 threshold, only method E demonstrated acceptable accuracies of 61.4% and 62.0% to identify a PW-IMR≥25 and Rmicro≥475WU, respectively.

Conclusion
All five angio-IMR methods demonstrated poor diagnostic accuracy compared to PW-IMR and Rmicro, highlighting significant limitations in their clinical utility.