| Part I Assessment of the physiological severity for coronary epicardial stenosis by using the angiography images dataObject i ve:Coronary flow reserve (CFR) and fractional flow reserve (FFR) are important physiological determinants for coronary disease in the clinical settings. However, the measurements currently require a sensor wire advanced across the stenosis. While an angiographic technique based on first-pass distribution analysis (FPA) and scaling laws can be used to measure CFR and FFR using only image data. The purpose of this study was to validate the CFR and FFR measurement techniques using only angiographic image data. Materials and Methods:Twelve swine were instrumented with an ultrasound flow probe on the left anterior descending artery (LAD). An extravascular occluder was used to produce stenosis. Contrast material injections were made into the left coronary artery during image acquisition. Volumetric blood flow from the flow probe (Qq), coronary pressure (Pa), distal coronary pressure (Pd) and right atrium pressure (Pv) were continuously recorded. Angiography-based blood flow (Qa) was calculated by using a time-density curve based on the FPA technique.①Flow probe based absolute CFR (aCFRq) and angiography based aCFR (aCFRa) were calculated as the ratio of hyperemic to baseline flow using Qq and Qa, respectively.②Relative angiographic FFR (rFFRa) was calculated as the ratio of the normalized Qa in LAD to the left circumflex artery (LCx) during hyperemia.③To determine the angiography-based FFR (FFRa), the ratio of blood flow in the presence of a stenosis (Qs) to theoretically normal blood flow (QN) was calculated. Qs was measured using a time-density curve and the assumption that blood was momentarily replaced with contrast agent during the injection. QN was estimated from the total coronary arterial volume using scaling laws. Flow probe-based FFR (FFRq) was measured from the ratio of flow with and without stenosis. Pressure-wire measurements of FFR (FFRP), which was calculated from the ratio of (Pd-Py) divided by (Pa-Py), were continuously obtained during the study. Resu I ts:aCFRa showed a strong correlation with the gold standard aCFRq (aCFRa=0.91aCFRq+0.30, r=0.90, p<0.0001). Relative FFRa correlated linearly with FFRq (relative FFRa=0.86FFRq+0.05, r=0.90, p<0.0001). FFRa showed a good correlation with FFRq (FFRa=0.97FFRq+0.06, r=0.86, p<0.001), although FFRP overestimated the FFRq (FFRp=0.686FFRq+0.271, r=0.87, p<0.0001). Additionally, the Bland-Altman analysis showed a close agreement between the angiographic and the gold standard flow probe indices. Conelusions:The quantification of CFR and FFR using angiographic image data was validated in a swine model. This angiographic technique, which does not require a wire across the stenosis, could potentially be used for coronary physiological assessment during routine cardiac catheterization. Part Ⅱ Assessment of Coronary Microcirculation in a Swine Animal ModelObjective:Structural coronary microcirculation abnormalities are important prognostic determinants in clinical settings. Several hemodynamic indices, such as absolute coronary flow reserve (aCFR), microvascular resistance (MR) and zero-flow pressure (Pzf). However, assessment of coronary microvascular system requires a velocity wire. A first-pass distribution analysis (FPA) technique to measure volumetric blood flow has previously been validated. The aim of this study was the in vivo validation of the MR measurement technique using FPA, to compare and establish the most reliable index to assess coronary microcirculation. Materials and Methods:Twelve anesthetized swine were instrumented with a transit-time ultrasound flow probe on the proximal segment of the left anterior descending (LAD) artery. A pressure wire was advanced into the distal LAD. Intravenous adenosine (400μg/kg/min) was used to produce maximum hyperemia. Microspheres were injected into the LAD to create a model of microvascular dysfunction. An occluder was used to produce stenosis. A region of interest in the LAD arterial bed was drawn to generate time-density curves using angiographic images. Volumetric blood flow measurements (Qa) 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 probe (Qq), aortic pressure (Pa), distal coronary pressure (Pd) and right atrium pressure (Pv) were continuously recorded. Flow probe based aCFR (aCFRq) and angiographic aCFR (aCFRa) were calculated using Qq and Qa, respectively. Flow probe based normalized MR (NMRq) and angiography based normalized MR (NMRa) were calculated using Qq and Qa, respectively during hyperemia. Pzf was calculated using Qq and Pd. Results:In258measurements, Qa showed a strong correlation with the gold standard Qq (Qa=0.90Qq+6.6ml/min, r=0.956, p<0.0001). NMRa correlated linearly with NMRq (NMRa=0.90NMRq+0.02mmHg/ml/min, r=0.956, p<0.0001). Additionally, the Bland-Altman analysis showed a close agreement between NMRa and NMRq. Two series of ROC curves were generated: normal epicardial artery model (N-model) and stenosis model (S-model). The areas under the ROC curves for aCFRq, aCFRa, NMRq, NMRa, Pzf were0.855,0.836,0.976,0.956,0.855in N-model and0.737,0.700,0.935,0.889,0.698in S-model. Both NMRq and NMRa were significantly more reliable than aCFR and Pzf in detecting the microvascular deterioration. Conelusions:A technique based on angiographic image data for quantifying NMR was validated using a swine model. Compared to aCFR and Pzf, NMR provided a more accurate assessment of microcirculation. This improved accuracy was more prevalent when stenosis existed. 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 as a less invasive method. |
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