Doppler Versus Thermodilution-Derived Coronary Microvascular Resistance to Predict Coronary Microvascular Dysfunction in Patients With Acute Myocardial Infarction or Stable Angina Pectoris

Coronary microvascular resistance is increasingly measured as a predictor of clinical outcomes, but there is no accepted gold-standard measurement. We compared the diagnostic accuracy of two invasive indices of microvascular resistance, Doppler-derived hyperemic microvascular resistance (hMR) and thermodilution-derived index of microcirculatory resistance (IMR), at predicting microvascular dysfunction. 54 patients (61±10 years) undergoing cardiac catheterization, for stable coronary artery disease (n=10) or acute myocardial infarction (AMI, n=44), had simultaneous intracoronary pressure, Doppler flow velocity and thermodilution flow data acquired from 74 unobstructed vessels, at rest and hyperemia. Three independent measures of microvascular function were assessed, using predefined dichotomous thresholds: i) CFR, the average value of Doppler- and thermodilution-derived coronary flow reserve (CFR), and cardiovascular magnetic resonance derived: ii) Myocardial Perfusion Reserve Index (MPRI) and iii) Microvascular Obstruction (MVO). hMR correlated with IMR (rho = 0.41, p<0.0001). hMR had better diagnostic accuracy than IMR to predict CFR (area under curve, (AUC) 0.82 versus 0.58, p<0.001, sensitivity/specificity 77/77% versus 51/71%) and MPRI (AUC 0.85 versus 0.72, p=0.19, sensitivity/specificity 82/80% versus 64/75%). In AMI patients, the AUCs of hMR and IMR at predicting extensive MVO were 0.83 and 0.72 respectively (p=0.22, sensitivity/specificity 78/74% versus 44/91%). We measured two invasive indices of coronary microvascular resistance to predict multiple distinct measures of microvascular dysfunction. We found these two invasive indices only correlate modestly and so cannot be considered equivalent. In our study, the correlation between independent invasive and non-invasive measures of microvascular function was better with hMR than with IMR.