Abstract ：

Objective: After coronary artery bypass grafting (CABG) surgery, the main causes of poor instant patency of left internal mammary arteries (LIMAs) are competitive flow and anastomotic stenosis, but how to determine the cause of LIMA non-patency without interfering with the native coronary artery is still a difficult problem to be solved urgently.Methods: In this study, a 0D-3D coupled multiscaled CABG model of anastomotic stenosis and competitive flow was constructed. After calculation, the flow waveform of the LIMA was extracted, and the waveform shape, common clinical parameters (average flow, PI, and DF), and graft flow FFT ratio results (F0/H1 and F0/H2) were analyzed.Results: For LIMA, these three common clinical parameters did not differ significantly between the anastomotic stenosis group and competitive flow group. However, the waveform shape and FFT ratio (especially F0/H2) of the competitive flow group were significantly different from those of the anastomotic stenosis group. When the cause was competitive flow, there was systolic backflow, and F0/H2 was too high (>14.89). When the cause was anastomotic stenosis, the waveform maintained a bimodal state and F0/H2 was in a normal state (about 1.17).Conclusion: When poor instant patency of the LIMA is found after CABG, the causes can be determined by graft flow waveform shape and F0/H2.

Keyword ：

graft patency multiscaled model lumped parameter model computational fluid dynamics coronary artery bypass grafting

Cite：

Copy from the list or Export to your reference management。

Abstract ：

Clinically, fractional flow reserve (FFR)-guided coronary artery bypass grafting (CABG) is more effective than CABG guided by coronary angiography alone. However, no scholars have explained the mechanism from the perspective of hemodynamics. Two patients were clinically selected; their angiography showed 70% coronary stenosis, and the FFRs were 0.7 (patient 1) and 0.95 (patient 2). The FFR non-invasive computational model of the two patients was constructed by a 0-3D coupled multiscaled model, in order to verify that the model can accurately calculate the FFR results. Virtual bypass surgery was performed on these two stenoses, and a CABG multiscaled model was constructed. The flow rate of the graft and the stenosis coronary artery, as well as the wall shear stress (WSS) and the oscillatory shear index (OSI) in the graft were calculated. The non-invasive calculation results of FFR are 0.67 and 0.91, which are close to the clinical results, which proves that our model is accurate. According to the CABG model, the flow ratios of the stenosis coronary artery to the graft of patient 1 and patient 2 were 0.12 and 0.42, respectively. The time-average wall shear stress (TAWSS) results of patient 1 and patient 2 grafts were 2.09 and 2.16 Pa, respectively, and WSS showed uniform distribution on the grafts. The OSI results of patients 1 and 2 grafts were 0.0375 and 0.1264, respectively, and a significantly high OSI region appeared at the anastomosis of patient 2. The FFR value of the stenosis should be considered when performing bypass surgery. When the stenosis of high FFR values is grafted, a high OSI region is created at the graft, especially at the anastomosis. In the long term, this can cause anastomotic blockage and graft failure.

Keyword ：

fractional flow reserve lumped parameter model hemodynamics coronary artery bypass grafting multiscale model

Cite：

Copy from the list or Export to your reference management。

Abstract ：

In the existing patency prediction model of coronary artery bypass grafting (CABG), the characteristics are based on graft flow, but no researchers selected hemodynamic factors as the characteristics. The purpose of this paper is to study whether the introduction of hemodynamic factors will affect the performance of the prediction model. Transit time flow-meter (TTFM) waveforms and 1-year postoperative patency results were obtained from 50 internal mammary arterial grafts (LIMA) and 82 saphenous venous grafts (SVG) in 60 patients. Taking TTFM waveforms as the boundary conditions, the CABG ideal models were constructed to obtain hemodynamic factors in grafts. Based on clinical characteristics and combination of clinical and hemodynamic characteristics, patency prediction models based on support vector machine (SVM) were constructed respectively. For LIMA, after the introduction of hemodynamic factors, the accuracy, sensitivity and specificity of the prediction model increased from 70.35%, 50% and 74.17% to 78.02%, 70% and 78.89%, respectively. For SVG, the accuracy, sensitivity and specificity of the prediction model increased from 63.24%, 40% and 76.91% to 74.41%, 60.1% and 82.73%, respectively. The performance of the prediction model can be improved by introducing hemodynamic factors into the characteristics of the model. The accuracy, sensitivity and specificity of the prediction results are higher with the addition of hemodynamic characteristics. (C) 2019 Elsevier Ltd. All rights reserved.

Keyword ：

Support vector machine Transit time flow-meter Hemodynamics Coronary artery bypass grafting Graft patency

Cite：

Copy from the list or Export to your reference management。

Abstract ：

Background: In coronary artery bypass grafting (CABG), the patency of venous sequential graft remains controversial. Hemodynamic factors have been proved to be the important factors influencing graft patency. The objective of this study is to compare the patency of sequential grafts and normal grafts by hemodynamic environment. Methods: This study used a patient's clinical data to construct a 0D/3D coupled multi-scale model, and used this model to calculate graft's hemodynamics under two grafting methods. Meanwhile, CABG ideal models were constructed based on grafts' flow data of 60 patients (63 normal grafts, 19 sequential grafts) to calculate grafts' hemodynamics. Results: Based on the multi-scale model, it was found that the sequential graft flow and time average wall shear stress (TAWSS) were higher than normal graft, which was good for graft patency. But there were a flow separation region, some regions of high oscillatory shear index (OSI) and relative residence time (RRT) in sequential graft, which could lead to intimal hyperplasia. Based on ideal CABG models, it was known that failure rate of sequential and normal grafts were 36.8% and 36.5%, and there were significant differences between them in flow rate, TAWSS and OSI (sequential versus normal: flow rate (ml/min): 42.26 +/- 17.98 versus 27.33 +/- 14.52, TAWSS (Pa): 0.71 +/- 0.28 versus 0.54 +/- 0.25, OSI: 0.0114 +/- 0.0029 versus 0.0047 +/- 0.0020). Conclusion: For saphenous venous graft (SVG), although the normal graft has similar patency with the sequential graft, the hemodynamic mechanism behind it is different. In flow rate and WSS, sequential grafts have an advantage over normal grafts. But there are high OSI and RRT regions in sequential grafts.

Keyword ：

transit time flow-meter Coronary artery bypass grafting graft patency multi-scale model sequential graft hemodynamics

Cite：

Copy from the list or Export to your reference management。

Abstract ：

In coronary artery bypass grafting (CABG), graft's poor instant patency may lead to an abnormal hemodynamic environment in anastomosis, which could further cause graft failure after the surgery. This paper investigates the graft hemodynamics with different instant patency, and explores its effect on graft postoperative efficiency. Six CABG 0D/3D coupling multi-scale models which used left internal mammary artery (LIMA) and saphenous vein (SVG) as grafts were constructed. Different types of grafts were examined in the models, including normal grafts, grafts with competitive flow and grafts with anastomotic stenosis. Simulation results indicated that comparing with SVG grafts, there was a greater difference between normal LIMA graft and non-patent LIMA graft. Also, the backflow occurred even in LIMA systolic flow. The wall shear stress (WSS) in the graft of the competitive flow LIMA model had an appreciable decrease comparing with the normal graft. In addition, the WSS in the stenosis region of the anastomotic stenosis LIMA model was much higher than its adjacent regions. In contrast, the WSS distributions in the SVG models were much smoother than in the LIMA models. For oscillatory shear index (OSI), there was little difference between normal LIMA and SVG. But when the graft had competitive flow or anastomotic stenosis, much higher OSI occurred in some regions in LIMA than SVG. There are significant differences in hemodynamics between normal grafts and non-patent grafts both in LIMA and SVG. The hemodynamic environment in a normal LIMA is better than that in a normal SVG. However, in the situation of the two types of non-patent grafts, the hemodynamics of SVG is better than LIMA.

Keyword ：

hemodynamics instant patency Coronary artery bypass grafting graft flow multi-scale model

Cite：

Copy from the list or Export to your reference management。

Abstract ：

Background: During coronary artery bypass grafting (CABG), the ratio of powers of the fundamental frequency and its first harmonic (F0/H1) in fast Fourier transformation (FFT) analysis of the graft's flow waves has been used in the field of evaluation of the patency in anastomosis. But there is no report about using the FFT method to evaluate the magnitude of competitive flow. This study is aiming at exploring the relationship between competitive flow and FFT analysis of the flow waves in left internal mammary artery (LIMA) graft, and finding a new method to evaluate the magnitude of competitive flow. Methods: At first, establishing the CABG multiscale models of different stenosis in left anterior descending artery (LAD) to get different magnitude of competitive flows. Then, calculating the models by ANSYS-CFX and getting the flow waves in LIMA. Finally, analyzing the flow waves by FFT method and comparing the FFT results with the magnitude of competitive flow. Results: There is no relationship between competitive flow and F0/H1. As for F0/ H2 and F0/H3, they both increase with the reduction of the stenosis in LAD. But the increase of F0/H3 is not obviously enough and it can't identify the significant competitive flow clearly, so it can't be used as the evaluation index. It is found that F0/ H2 increases obviously with the increase of the competitive flow and can identify the significant competitive flow. Conclusion: The FFT method can be used in the evaluation of competitive flow and the F0/H2 is the ideal index. High F0/H2 refers to the significant competitive flow. This method can be used during CABG to avoid the risk of competitive flow.

Keyword ：

Competitive flow CABG FFT

Cite：

Copy from the list or Export to your reference management。

Abstract ：

Background: Sequential and single grafting are two surgical procedures of coronary artery bypass grafting. However, it remains unclear if the sequential graft can be used between the right and left coronary artery system. The purpose of this paper is to clarify the possibility of right coronary artery system anastomosis to left coronary system. Methods: A patient-specific 3D model was first reconstructed based on coronary computed tomography angiography (CCTA) images. Two different grafts, the normal multi-graft (Model 1) and the novel multi-graft (Model 2), were then implemented on this patient-specific model using virtual surgery techniques. In Model 1, the single graft was anastomosed to right coronary artery (RCA) and the sequential graft was adopted to anastomose left anterior descending (LAD) and left circumflex artery (LCX). While in Model 2, the single graft was anastomosed to LAD and the sequential graft was adopted to anastomose RCA and LCX. A zero-dimensional/three-dimensional (0D/3D) coupling method was used to realize the multi-scale simulation of both the pre-operative and two post-operative models. Results: Flow rates in the coronary artery and grafts were obtained. The hemodynamic parameters were also showed, including wall shear stress (WSS) and oscillatory shear index (OSI). The area of low WSS and OSI in Model 1 was much less than that in Model 2. Conclusions: Model 1 shows optimistic hemodynamic modifications which may enhance the long-term patency of grafts. The anterior segments of sequential graft have better long-term patency than the posterior segments. With rational spatial position of the heart vessels, the last anastomosis of sequential graft should be connected to the main branch.

Keyword ：

Sequential graft Computational fluid dynamic (CFD) Hemodynamics Multi-branch

Cite：

Copy from the list or Export to your reference management。

Abstract ：

Sequential graft was used frequently in clinical studies. In this study, the hemodynamic effect of one kind of sequential graft in two different conditions of the lesion was discussed and some recommendations on the surgical procedures were made. A patient-specific three-dimensional (3D) model of left anterior descending artery (LAD) was reconstructed. A moderate stenosis exist in the trunk of LAD between the first and the second diagonal branch (D1 and D2). Another 3D model without stenosis was also reconstructed based on the patient-specific model. Sequential graft and single graft were applied on these two 3D model. Thus four 3D models were built so that the hemodynamic effect of sequential graft can be discussed. The zero-dimensional (0D)/3D coupling method was used to perform the numerical simulation by coupling the 3D artery model with a 0D lumped parameter model of the cardiovascular system. The flow rates in the branches of LAD and the graft flow were calculated and illustrated in this paper. The wall shear stress (WSS) and oscillatory shear index (OSI) were also calculated and depicted. If the native LAD is stenosis, sequential graft should be applied for the short-term outcomes. Moreover, the long-term patency of the sequential graft applied on the stenosis LAD is good. The long-term patency of the single graft was bad. But the short-term outcomes are almost the same when LAD is not stenosis. If no stenosis exist in the native LAD, a graft with smaller diameter should be applied to improve the long-term patency.

Keyword ：

hemodynamics computational fluid dynamics (CFD) coronary artery bypass grafting (CABG) 0D/3D coupling simulation Sequential graft

Cite：

Copy from the list or Export to your reference management。

Abstract ：

Purpose: The internal thoracic artery is the choice of graft for coronary artery bypass grafting due to the excellent long-term patency. However internal thoracic artery graft failures still occur due to diffuse narrowing, known as the string phenomenon. Studies suggest that the string phenomenon is caused by competitive flow when the coronary stenosis is not serious, but the hemodynamics of the string phenomenon are still unclear. The purpose of this study is to clarify the hemodynamic characteristics of the string phenomenon. Materials: A patient-specific 3-dimensional model of the aortic arch and coronary arteries was reconstructed. A moderate stenosis was applied to the left anterior descending artery. The internal thoracic artery was used to bypass the stenosis. Two further 3D models were built to study the hemodynamics of the string phenomenon. Methods: A numerical study was performed by coupling the 3D artery model with 0-dimensional lumped parameter model of the cardiovascular system. Results: The graft flow, native coronary flow, wall shear stress and oscillatory shear index were calculated and illustrated. Inverse flow and high oscillatory shear index appeared on the internal thoracic artery graft when the stenosis was moderate. Conclusion: High oscillatory shear index might be the major hemodynamic characteristic of the string phenomenon in internal thoracic artery graft. The inverse graft flow and,the difference in graft flow caused by clamping the stenosis can be used to evaluate the probability of observing the string phenomenon. (C) 2015 Elsevier Ltd. All rights reserved.

Keyword ：

Internal thoracic artery graft Coronary artery bypass grafting (CABG) Computational fluid dynamics (CFD) 0D/3D coupling simulation Hemodynamics

Cite：

Copy from the list or Export to your reference management。

Abstract ：

Background. Single ventricle disease is treated by Glenn surgery. It is generally accompanied by stenosis on a pulmonary artery or its branches, which has great effect on hemodynamics. This study investigated the hemodynamic influence of different pulmonary stenosis degree in Glenn procedure. Materials. Four three-dimensional Glenn models with different left pulmonary artery stenosis rates as, respectively, 0% (model 1), 25% (model 2), 50% (model 3), and 75% (model 4) by the diameter were generated. Method. Geometric multiscale analysis method was used in the numerical simulations by coupling the lumped parameter model (LPM) and three-dimensional model. Results. During one cardiac cycle, the flow ratio between left pulmonary artery and superior vena cava was about 0.49 for models 1, 2, and 3, while the ratio decreased to 0.34 for model 4. On the other hand, hemodynamics parameters like power loss and oscillation shear index show complications of the stenosis to the postoperative development. Conclusion. When the stenosis rate is above 75%, it is suggested to treat stenosis before Glenn procedure, while when the stenosis rate is below 50%, there is no necessity to pay attention to it due to the little effect it makes.

Cite：

Copy from the list or Export to your reference management。