Angiography-derived index of microcirculatory resistance (IMR angio ) 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 angio ) 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 angio (NH-IMR angio ) 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 angio and NH-IMR angio was derived using quantitative flow ratio. In patients with STEMI, cardiac magnetic resonance was performed to quantify microvascular obstruction (MVO). IMR angio 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 ROC = 0.93 [0.88–0.98]; NSTE-ACS AUC ROC = 0.77 [0.63–0.92]; CCS AUC ROC = 0.88 [0.79–0.97]). Agreement between the two indices was evident on Bland Altman analysis. In STEMI, NH-IMR angio was also well correlated with IMR (rho = 0.64, p < 0.0001), with good diagnostic accuracy in predicting high invasive IMR (AUC ROC = 0.82 [0.74–0.90]). Both IMR angio (AUC ROC = 0.74 [0.59–0.89]) and NH-IMR angio (AUC ROC = 0.76 [0.54–0.87]) were significantly associated with MVO in STEMI. In conclusions, IMR angio is a valid alternative to invasive IMR to detect CMD in patients with acute and stable coronary syndromes, whilst NH-IMR angio has a good diagnostic accuracy in STEMI where it could become a user-friendly diagnostic tool as it is adenosine-free.