Angiography-derived assessment of coronary microcirculatory resistance in patients with suspected myocardial ischaemia and non-obstructive coronary arteries

Myocardial ischaemia with non-obstructive coronary arteries (INOCA) represents a challenging and frequent, but largely underdiagnosed, condition.We aimed to investigate the feasibility and diagnostic value of angiography-derived coronary microcirculatory resistance in patients with INOCA syndrome.This is an investigator-driven, prospective and blinded study. The diagnostic yield of angiography-derived index of coronary microcirculatory resistance (angio-IMR) was investigated against thermodilution-derived IMR (thermo-IMR) in patients with clinically indicated coronary angiography due to suspected myocardial ischaemia and angiographically normal or non-obstructive coronary arteries. The angio-IMR was derived from resting angiograms (contrast-flow angio-IMR [cAngio-IMR]) by an expert analyst blinded to the thermo-IMR. An independent, blinded, physiology core laboratory analysed the raw intracoronary physiology data and provided the final thermo-IMR values.A total of 104 patients (108 coronary vessels) were analysed after fulfilling predefined inclusion criteria. Most patients were female (67%). Obstructive epicardial disease was angiographically (percent diameter stenosis <50%) and physiologically (fractional flow reserve>0.80) ruled out in all cases. Median thermo-IMR and cAngio-IMR were 16.6 (12.7, 23.0) and 16.8 (12.8, 23.1) units, respectively (median difference -0.31, 95% confidence interval: -1.53 to 1.00; p=0.654). cAngio-IMR showed good correlation (Pearson coefficient 0.76; p<0.001), agreement (mean bias 0.4), discriminatory power (area under the curve from the receiver operator characteristics 0.865; p<0.001) and accuracy (85%), compared to thermo-IMR (≥25 U).Evaluating coronary microcirculatory resistance in patients with INOCA syndrome using cAngio-IMR is feasible and accurate. By circumventing the need of coronary instrumentation and hyperaemic drugs, this method may facilitate the assessment of coronary microcirculatory resistance in patients with suspected INOCA.gov: NCT04827498.