Angiography-derived index of microcirculatory resistance (IMR) as a novel pressure-wire-free tool to assess coronary microvascular dysfunction in acute coronary syndromes and stable coronary artery disease.

To investigate the diagnostic accuracy of (1) hyperaemic angiography-derived index of microcirculatory resistance (IMR) in defining coronary microvascular dysfunction (CMD) across patients with acute coronary syndromes (ST-elevation myocardial infarction [STEMI]; non-ST elevation acute coronary syndrome [NSTE-ACS]) and stable chronic coronary syndrome [CCS]) and (2) the accuracy of non-hyperaemic IMR (NH-IMR) to detect CMD in STEMI. 145 patients (STEMI = 66; NSTEMI = 43; CCS = 36) were enrolled. 246 pressure-wire IMR measurements were made in 189 coronary vessels. IMR and NH-IMR was derived using quantitative flow ratio. In patients with STEMI, cardiac magnetic resonance was performed to quantify microvascular obstruction (MVO). IMR was correlated with IMR (overall rho = 0.78, p < 0.0001; STEMI, rho = 0.85 p < 0.0001; NSTE-ACS and rho = 0.72, p < 0.0001; CCS, rho = 0.70, p < 0.0001) and demonstrated good diagnostic performance in predicting high IMR (STEMI AUC = 0.93 [0.88-0.98]; NSTE-ACS AUC = 0.77 [0.63-0.92]; CCS AUC = 0.88 [0.79-0.97]). Agreement between the two indices was evident on Bland Altman analysis. In STEMI, NH-IMR was also well correlated with IMR (rho = 0.64, p < 0.0001), with good diagnostic accuracy in predicting high invasive IMR (AUC = 0.82 [0.74-0.90]). Both IMR (AUC = 0.74 [0.59-0.89]) and NH-IMR (AUC = 0.76 [0.54-0.87]) were significantly associated with MVO in STEMI. In conclusions, IMR is a valid alternative to invasive IMR to detect CMD in patients with acute and stable coronary syndromes, whilst NH-IMR has a good diagnostic accuracy in STEMI where it could become a user-friendly diagnostic tool as it is adenosine-free.