Abstract
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 2 invasive indices of microvascular resistance, Doppler-derived hyperemic microvascular resistance (hMR) and thermodilution-derived index of microcirculatory resistance (IMR), at predicting microvascular dysfunction. A total of 54 patients (61 ± 10 years) who underwent cardiac catheterization for stable coronary artery disease (n = 10) or acute myocardial infarction (n = 44) had simultaneous intracoronary pressure, Doppler flow velocity and thermodilution flow data acquired from 74 unobstructed vessels, at rest and during hyperemia. Three independent measurements of microvascular function were assessed, using predefined dichotomous thresholds: (1) coronary flow reserve (CFR), the average value of Doppler- and thermodilution-derived CFR; (2) cardiovascular magnetic resonance (CMR) derived myocardial perfusion reserve index; and (3) CMR-derived microvascular obstruction. 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 vs 0.58, p <0.001, sensitivity and specificity 77% and 77% vs 51% and 71%) and myocardial perfusion reserve index (AUC 0.85 vs 0.72, p = 0.19, sensitivity and specificity 82% and 80% vs 64% and 75%). In patients with acute myocardial infarction, the AUCs of hMR and IMR at predicting extensive microvascular obstruction were 0.83 and 0.72, respectively (p = 0.22, sensitivity and specificity 78% and 74% vs 44% and 91%). We conclude that these 2 invasive indices of coronary microvascular resistance only correlate modestly and so cannot be considered equivalent. In our study, the correlation between independent invasive and noninvasive measurements of microvascular function was better with hMR than with IMR.
Highlights
In the enrolled population, the hyperemic microvascular resistance (hMR) was 2.60 (1.99 to 3.43) mm Hg·cm-1·s and the index of microcirculatory resistance (IMR) was 19.0 (13.0 to 29.8) U. hMR significantly correlated with IMR
HMR had superior diagnostic accuracy over IMR to predict the presence of any MVO, but this difference was not significant (AUC 0.75 vs 0.66). This is the first study in humans to have simultaneously assessed the correlation of 2 invasive indices of MVR, Doppler-derived hMR and thermodilution-derived IMR, against each other and against independent measurements of MVD
The main findings of this study are (1) hMR and IMR correlate modestly with each other, and cannot be considered equivalent predictors of MVD; (2) hMR had superior diagnostic accuracy over IMR to predict MVD determined invasively by coronary flow reserve (CFR); (3) hMR had a clinically superior sensitivity over IMR to predict MVD determined by cardiac magnetic resonance-derived myocardial perfusion reserve index (MPRI) and extensive MVO, but there were no statistically significant differences observed; (4) an hMR threshold of ≥2.5 mm Hg·cm-1·s and an IMR threshold from 21.5 to 24 U were optimal for predicting MVD determined by CFR and MPRI; (5) in the infarct related artery after an acute myocardial infarction (AMI), an hMR threshold of ≥3.25 mm Hg·cm-1·s and an IMR threshold of ≥40 U were optimal for predicting MVD determined by extensive MVO
Summary
ComboWires were provided by Volcano Corporation (San Diego, California). The American Journal of Cardiology (www.ajconline.org) of microcirculatory resistance (IMR)[5] estimates flow with thermodilution, whereas hyperemic microvascular resistance (hMR) incorporates Doppler flow velocity.[6] Both indices have separately been shown to predict infarct size,[7,8] MVO,[8] regional wall motion,[7] and adverse left ventricular (LV) remodeling.[7] to date, no study has compared hMR and IMR against invasive and noninvasive measurements of MVD in humans.
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