Comparison of angiography-derived index of microcirculatory resistance measurements between low and high frame-rate acquisitions: The prospective ADMIRAL-study

Abstract

Introduction

Angiography-derived index of microcirculatory resistance (angio-IMR) is a novel, wire-free, angiography-based method (QFR-IMR®) to assess coronary microvascular dysfunction. If a frame-rate of 15 frames per second (fps) is recommended, there is an interest in decreasing this frame-rate to reduce X-ray exposure. However, the impact of frame-rate reduction on angio-IMR quantification has not been investigated.

Objective

To compare angio-IMR at 7.5 fps (angio-IMR low) to angio-IMR at 15 fps (angio-IMR high) in a multicentric study.

Method

From October 2023 to February 2024, we conducted a multicentre prospective study including consecutive patients referred for an invasive coronary angiogram with a final diagnosis of ischemia with no obstructive coronaries arteries (INOCA) or acute coronary syndrome (ACS). In ACS patients, angio-IMR was measured after revascularisation. The same two acquisitions were recorded at a rate of 7.5 fps and a rate of 15 fps to measure angio-IMR in the selected vessel (culprit coronary vessel in ACS patients or left anterior descending artery in patients with INOCA). Angio-IMR was measured with dedicated software (QFR-IMR® RE, Medis Medical Imaging). Correlation between angio-IMR low and angio-IMR high was then assessed, as well as the diagnostic accuracy of angio-IMR low to predict microcirculatory dysfunction (defined as angio-IMR high≥ 25 for INOCA and ≥ 40 for ACS). Statistical significance was awarded by P≤0.05.

Results

Among 75 patients, 57 ACS and 18 INOCA were included (mean age 61 ± 12 years, 72% male). Angio-IMR low (median = 35; [IQR: 28–48]) was slightly but significantly higher (P = 0.04) than angio-IMR high (median = 34; [IQR: 25–45]). Angio-IMR low and angio-IMR high were significantly correlated (r = 0.90; P < 0.0001) as showed in Fig. 1. Using angio-IMR high to diagnose microcirculatory dysfunction as reference, angio-IMR low achieved positive and negative predictive values of 83% and 85% respectively with 63 concordant patients, 6 false positives, and 6 false negatives.

Conclusion

Correlation between angio-IMR high and angio-IMR low is good even if angio-IMR low measurement is slightly higher than angio-IMR high. Lowering frame acquisition rate reduces radiation exposure without relevantly impact on the diagnostic accuracy of angio-IMR.