Coronary microcirculation assessment using functional angiography: Development of a wire‐free method applicable to conventional coronary angiograms

Objectives We aimed to develop a novel wire‐ and adenosine‐free microcirculatory resistive index from functional angiography (angio‐IMR) to estimate coronary microcirculatory resistance, and to investigate how this method can improve clinical interpretation of physiological stenosis assessment with quantitative flow ratio (QFR). Background Hyperemic index of coronary microcirculatory resistance (IMR) is a widely used tool to assess microcirculatory dysfunction. However, the need of dedicated intracoronary wire and hyperemia limits its adoption in clinical practice. Methods We performed our study in two separate stages: (1) development of a formula (angio‐IMR) to estimate IMR from resting angiograms and aortic pressure (Pa), and (2) validation of the method in a clinical population using invasively measured IMR as reference. Additionally, QFR diagnostic performance was assessed considering angio‐IMR values. Results We developed the formula: angio‐IMR = (Pa–[0.1*Pa])*QFR*e‐Tmn (where e‐Tmn is an estimation of hyperaemic mean transit time) and validated it in 115 vessels (104 patients). Angio‐IMR correlated well with IMR (Spearman's rho = 0.70, p