Zhang Z, Takarada S, Molloi S. Quantification of coronary microvascular resistance using angiographic images for volumetric blood flow measurement: in vivo validation. Am J Physiol Heart Circ Physiol 300: H2096 -H2104, 2011. First published March 11, 2011 doi:10.1152/ajpheart.01123.2010.-Structural coronary microcirculation abnormalities are important prognostic determinants in clinical settings. However, an assessment of microvascular resistance (MR) requires a velocity wire. A first-pass distribution analysis technique to measure volumetric blood flow has been previously validated. The aim of this study was the in vivo validation of the MR measurement technique using first-pass distribution analysis. Twelve anesthetized swine were instrumented with a transit-time ultrasound flow probe on the proximal segment of the left anterior descending coronary artery (LAD). Microspheres were injected into the LAD to create a model of microvascular dysfunction. Adenosine (400 g·kg Ϫ1 ·min Ϫ1 ) was used to produce maximum hyperemia. A region of interest in the LAD arterial bed was drawn to generate time-density curves using angiographic images. Volumetric blood flow measurements (Q a) were made using a time-density curve and the assumption that blood was momentarily replaced with contrast agent during the injection. Blood flow from the flow probe (Qp), coronary pressure (Pa), and right atrium pressure (Pv) were continuously recorded. Flow probe-based normalized MR (NMRp) and angiography-based normalized MR (NMRa) were calculated using Qp and Qa, respectively. In 258 measurements, Qa showed a strong correlation with the gold standard Qp (Qa ϭ 0.90 Qp ϩ 6.6 ml/min, r 2 ϭ 0.91, P Ͻ 0.0001). NMRa correlated linearly with NMRp (NMRa ϭ 0.90 NMRp ϩ 0.02 mmHg·ml Ϫ1 ·min Ϫ1 , r 2 ϭ 0.91, P Ͻ 0.0001). Additionally, the BlandAltman analysis showed a close agreement between NMRa and NMRp. In conclusion, a technique based on angiographic image data for quantifying NMR was validated using a swine model. This study provides a method to measure NMR without using a velocity wire, which can potentially be used to evaluate microvascular conditions during coronary arteriography. coronary microvasculation CORONARY MICROVASCULAR DYSFUNCTION occurs in a number of myocardial disease states and has important prognostic implications in different clinical settings, including acute coronary syndromes, diabetic coronary disease, hypertrophic cardiomyopathy, and transplant cardiac allograft vasculopathy (25,26,39). Intracoronary physiological techniques have been advocated and several indexes for the assessment of changes in the microcirculatory bed have been proposed (2, 11, 51), such as coronary flow reserve (CFR) (9, 13, 34) and microvascular resistance (MR) (12,39,49). Many previous study findings suggest that MR is a useful variable for directly assessing microcirculatory function. In 1974, Gould et al. (19, 20, 21) postulated a hypothesis that minimum MR is independent of epicardial stenosis severity. Recently, Fearon and colleagues (1,7,12,14...
