Anastomosis Angle Research Articles

Optimum anastomosis angle of end-to-side microsurgical anastomosis for preventing future shear-related risk of thrombosis by computationalmodeling

End-to-side (ETS) microsurgical anastomosis is a powerful technique in microsurgery. It can overcome vessel’s diameter discrepancy and preserve the distal blood flow. Optimal angle of the ETS anastomosis has been debated and studied, and is currently limited to animal models. Computational model using Finite Element Analysis (FEA) was used to simulate the models with 45 (model45), 90 (model90), and 135 (model135) ETS anastomosis angles. Flow dynamics including flow velocity and wall shear rate were studied and compared. Maximum flow velocity ranged from the highest to the lowest in model135, model90, and model45, respectively. The velocity in model135 showed fluctuation flow. The maximum wall shear rate and distribution were highest in model45 and lowest in model90. ETS anastomosis angle of 90 degrees provided the most favourable flow dynamics to prevent shear related thrombosis in comparison to ETS anastomosis at 45 and 135 degrees.

#806 Predicting arteriovenous fistula success using ferumoxytol-enhanced MRI (Fe-MRI) and computational flow dynamics (CFD)

Abstract Background and Aims Arteriovenous fistula (AVF) failure is common and is invariably associated with preexisting anatomic problems of the inflow and outflow circuit. Ferumoxytol, an iron oxide nanoparticle, provides a safe alternative to gadolinium contrast material for MR angiography in chronic kidney disease (CKD). Computational fluid dynamics (CFD) has been utilised to virtually demonstrate the haemodynamics within AVFs using high-quality vascular mapping obtained with ferumoxytol-enhanced MRI (Fe-MRI). Using Fe-MRI and CFD we aimed to assess AVF haemodynamics and identify flow patterns and geometries associated with AVF success. Method In this pilot study we used Fe-MRI datasets of CKD patients who had vascular mapping 6 weeks after AVF creation. Using CFD methods we performed vessel segmentation to construct three-dimensional (3D) patient-specific geometries from images obtained with Fe-MRI (Fig. 1). We then completed a detailed CFD analysis for each AVF geometry to establish the associations of haemodynamic (mean wall shear stress (WSS), oscillatory shear index (OSI), blood flow velocity, and areas of abnormal flow) and anatomical parameters (anastomosis angle, feeding artery diameter, feeding artery curvature, draining vein diameter, and draining vein curvature) with AVF outcomes. The primary outcome was AVF success defined as AVF use (assisted or unassisted) for dialysis for a minimum of 3 months. ROC analysis was used to assess anatomical predictors of AVF flows of ≥1000 ml/min. Results The study included 17 patients with CKD who had AVF creation between 2018 and 2020. From these, 13 AVFs were successfully used for dialysis and 4 failed to mature or were used for dialysis for <3 months before failure. Compared to failed fistulas, successful AVFs had higher mean WSS and OSI. Failed AVFs were characterised by different haemodynamic patterns including lower flow rates with less helical flows. On ROC analysis the three metrics with the highest area under the curve (AUC) values were the feeding artery curvature (0.82), feeding artery diameter (0.76), and draining vein diameter (0.74) with a combined AUC value of 0.83 (Fig. 2). Conclusion Using Fe-MRI and CFD in the post-surgical juxta-anastomotic environment higher mean WSS and OSI were predictive of AVF success. In addition, the feeding artery curvature, feeing artery and draining vein diameters are strongly correlated with high venous flow rates, one of the key factors of AVF success. Although vessel diameters are routinely measured as part of pre-operative vascular mapping, a greater emphasis should be given on mean WSS, OSI and feeding artery vessel curvature when selecting vessels for AVF creation.

Morphology of the native ascending aorta after the Norwood procedure for aortic atresia: impact on survival and right ventricular dysfunction.

Our goal was to evaluate the impact of variable morphology of the native ascending aorta after the Norwood I procedure in patients with hypoplastic left heart syndrome/aortic atresia on long-term survival and systemic right ventricular dysfunction. Of 151 survivors of the Norwood procedure for hypoplastic left heart syndrome/aortic atresia at our institution between January 2001 and December 2020, we included patients with available and measurable aortograms prior to stage II palliation. The diameter of the native ascending aorta, the length of the native ascending aorta and the angle between the native ascending aorta and the proximal pulmonary artery were measured. We investigated the impact of these morphologic parameters on mortality and on right ventricular dysfunction (defined as at least moderate). Angiograms were available for 78 patients. The median diameter of the native ascending aorta was 3.2 mm (2.6-3.7), the median length of the native ascending aorta was 15.4 mm (13.3-17.9) and the median angle between the native ascending aorta and the proximal pulmonary artery was 44° (35°-51°). During the median follow-up of 6.5 years, 8 (10%) patients died and systemic right ventricular dysfunction occurred in 19 patients (24%). No significant association between aortic morphology and mortality could be detected. Right ventricular function was negatively affected by a larger angle between the native ascending aorta and the proximal pulmonary artery [odds ratio 1.07 (1.01-1.14), P = 0.02]. In survivors of the Norwood procedure for hypoplastic left heart syndrome/aortic atresia with available angiograms, no significant association between native aortic morphology and mortality could be demonstrated after stage II palliation, within the scope of this limited study. A larger anastomosis angle between the native ascending aorta and the proximal pulmonary artery emerged as a risk factor for right ventricular dysfunction.

Computational fluid-structure interaction analysis of the end-to-side radio-cephalic arteriovenous fistula

Background and ObjectiveIn the current work, we present a descriptive fluid-structure interaction computational study of the end-to-side radio-cephalic arteriovenous fistula. This allows us to account for the different thicknesses and elastic properties of the radial artery and cephalic vein. MethodsThe core of the work consists in simulating different arteriovenous fistula configurations obtained by virtually varying the anastomosis angle, i.e. the angle between the end of the cephalic vein and the side of the radial artery. Since the aim of the work is to understand the blood dynamics in the very first days after the surgical intervention, the radial artery is considered stiffer and thicker than the cephalic vein. ResultsOur results demonstrate that both the diameter of the cephalic vein and the anastomosis angle play a crucial role to obtain a blood dynamics without re-circulation regions that could prevent fistula failure. ConclusionsWhen an anastomosis angle close to the perpendicular direction with respect to the radial artery is combined with a large diameter of the cephalic vein, the recirculation regions and the low Wall Shear Stress (WSS) zones are reduced. Conversely, from a structural point of view, a low anastomosis angle with a large diameter of the cephalic vein reduces the mechanical stress acting on the vessel walls.

Surgical Modulation of Pulmonary Artery Shear Stress: A Patient-Specific CFD Analysis of the Norwood Procedure.

This study created 3D CFD models of the Norwood procedure for hypoplastic left heart syndrome (HLHS) using standard angiography and echocardiogram data to investigate the impact of shunt characteristics on pulmonary artery (PA) hemodynamics. Leveraging routine clinical data offers advantages such as availability and cost-effectiveness without subjecting patients to additional invasive procedures. Patient-specific geometries of the intrathoracic arteries of two Norwood patients were generated from biplane cineangiograms. "Virtual surgery" was then performed to simulate the hemodynamics of alternative PA shunt configurations, including shunt type (modified Blalock-Thomas-Taussig shunt (mBTTS) vs. right ventricle-to-pulmonary artery shunt (RVPAS)), shunt diameter, and pulmonary artery anastomosis angle. Left-right pulmonary flow differential, Qp/Qs, time-averaged wall shear stress (TAWSS), and oscillatory shear index (OSI) were evaluated. There was strong agreement between clinically measured data and CFD model output throughout the patient-specific models. Geometries with a RVPAS tended toward more balanced left-right pulmonary flow, lower Qp/Qs, and greater TAWSS and OSI than models with a mBTTS. For both shunt types, larger shunts resulted in a higher Qp/Qs and higher TAWSS, with minimal effect on OSI. Low TAWSS areas correlated with regions of low flow and changing the PA-shunt anastomosis angle to face toward low TAWSS regions increased TAWSS. Excellent correlation between clinically measured and CFD model data shows that 3D CFD models of HLHS Norwood can be developed using standard angiography and echocardiographic data. The CFD analysis also revealed consistent changes in PA TAWSS, flow differential, and OSI as a function of shunt characteristics.

International survey of radiocephalic arteriovenous fistula: ISRAF survey.

The objective of this survey was to encompass the full scope of international practice, entailing all technical, non-technical, preoperative stratification and functional maturation (FM) of RCAVF. The survey contained n = 19 questionnaires with n = 46 variables completed by n = 85 providers from n = 21 nations across n = 5 continents. The numerical values were subjected to mean with standard error whereas the nominal data to a non-parametric (Kruskal-Wallis & Spearman correlation test) and analysis of variance (ANOVA). The test of homogeneity, & probability was reported 95% confidence intervals (CI) alongside error plots. Furthermore, a decision and higher attribute tree model was constructed based on current survey for higher FM in RCAVF. FM is independently associated with volume of surgeon per year (procedures performed) (p < 0.01) [High Volume: 73% (95% CI, 68-77%) versus Average volume: 63% (95% CI, 59-66%) vs Low volume: 56% (95% CI, 51-61%)]. FM increased by 8% with every 20 more procedures per group of surgeons on end point of FM. Amongst continents: Australia, America, Asia and South America demonstrated higher FM to Africa & Europe (p < 0.05). UK possessed a lower FM 58% (95% CI, 48-68%) in comparison to the world & Europe respectively [65% (95% CI, 61-70%) vs 61% (95% CI, 58--65%)]. There was a positive causal link between angle of anastomosis at 30-76° (p < 0.01), longitudinal & S-shaped incision & arteriotomy length of 3 & 4 mm to higher FM (p < 0.05). FM in RCAVF is independently & incrementally associated with the volume of surgeon per year. There is a diverse inclusion, exclusion and technical approach in RCAVF creation. This survey advocates the importance of international collaboration and/or registry in assimilation, consolidate and development of consensus.

Comparative analysis of RADAR vs. conventional techniques for AVF maturation in patients with blood viscosity and vessel elasticity-related diseases through fluid-structure interaction modeling: Anemia, hypertension, and diabetes.

This study aims to compare two surgical techniques, the standard Vein-to-Artery and the newer Artery-to-Vein (Radial Artery Deviation And Reimplantation; RADAR), for enhancing the success of Arterio-Venous Fistula maturation in end-stage renal disease patients. The impact of diseases like anemia, diabetes, hypertension, and chronic kidney disease were considered. The goals are to advance Arterio-Venous Fistula (AVF) surgery, improve patient outcomes, and contribute to evidence-based surgical guidelines. Fluid-structure interaction modeling was employed to investigate how hemodynamic and mechanical stresses impact arteriovenous fistula maturation, with a particular focus on the role of wall shear stress in determining maturation outcomes. The critical threshold for vessel injury was identified as wall shear stress values exceeding 35 N/m2, while stenosis formation was projected to occur at levels below 1 N/m2. This work introduced a novel approach by considering disease-related factors, including blood viscosity (anemia), and vessel elasticity (diabetes, hypertension, and chronic kidney diseases), which directly influence hemodynamics and the generation of wall shear stress. Furthermore, the model was designed to incorporate varying thicknesses and elasticities for both the vein and artery, accurately representing authentic vascular anatomy. The RADAR technique has demonstrated superior performance compared to the standard technique by providing appropriate wall shear stress in critical regions and minimizing the risk of wall damage. Its use of a thicker vessel also reduces the risk of vessel injury, making it particularly effective for patients with Chronic Kidney Disease (CKD), hypertension, anemia, and diabetes, ensuring optimal blood flow and fewer complications. However, there are minor concerns about stenosis formation in hypertension and anemia cases, which could be mitigated by adjusting the anastomosis angle to be lower than 30°. Diabetes and hypertension have significant physiological effects that increase the risks associated with arteriovenous fistula maturation. The anemic condition resulting from CKD may help reduce vessel injury but raises concerns about potential stenosis formation. Despite these co-morbidities, the RADAR technique has demonstrated its ability to induce more favorable hemodynamic changes, promoting arteriovenous fistula maturation.

Proximal Clipping and Distal High-Flow Bypass in the Treatment of Giant/Complex Intracranial Aneurysm: An Opportunity or a Risk from a Fluid-Structural Interaction Analysis.

Conventional clipping and endovascular treatment are difficult to apply for some giant intracranial aneurysms (GIAs), and sometimes extracranial-to-intracranial (EC-IC) bypass becomes the optional choice. However, not all GIA patients can benefit from it. This study aims to recognize the underlying problems. We included eligible patients in our care. Then, we researched from three levels: a retrospective review of clinical data, fluid-structural analysis from two representative patient-specific models, and fluid-structural interaction analysis for idealized models to investigate the hemodynamic and biomechanical mechanisms. In this article, we report nine patients with GIA who underwent EC-IC surgery. Of them, three experienced dangerous postoperative hemorrhage, and one patient died. Among these three patients, two lacked the A1 segment of the anterior cerebral artery (ACA). The numerical simulation showed that after surgery, for the patient with an unruptured aneurysm and existence of ACA, the wall deformation, wall stress, pressure, and area of the oscillatory shear index (OSI) > 0.2 were decreased by 43%, 39%, 33%, and 13%, while the patient without A1 segment having postoperative hemorrhage showed 36%, 45%, 13%, and 55% increased, respectively. Thus, we postulated a dangerous "stump phenomenon" in such conditions and further demonstrated it from idealized models with different sizes of ACA. Finally, we found a larger anastomosis angle and smaller diameter of the graft can alleviate this effect. Neurosurgeon should cautiously evaluate the opportunity and risk for such patients who have aplasia of the A1 segment of ACA when making clinical decisions.

Evaluation of the Effects of Anastomosis Angle on the Performance of an Optimized Spiral Flow-Inducing Graft Design using CFD

Bypass grafting is a common medical intervention used for people suffering from atherosclerosis, but the prevalence of graft failure due to disturbed hemodynamics necessitates the improvement of graft design for optimum blood flow. Spiral flow has been proposed as a mechanism to improve hemodynamics in grafts. A previous study optimized a spiral flow-inducing graft design, but it did not consider the effects of anastomosis angle despite its significant effects on blood flow. The purpose of this research is to further enhance the performance and patency of bypass grafts by determining how the anastomosis angle affects the hemodynamics of a spiral flow-inducing graft design using computational fluid dynamics (CFD). Distal anastomoses of 6 mm ridged graft and femoral artery constructs at varying anastomosis angles of 15° increments were analysed using steady-state CFD analysis under the assumptions of laminar, isothermal, stationary, rigid, non-Newtonian, and incompressible flow to determine the anastomosis angle that would yield optimum flow parameters. A 30° anastomosis angle was found to yield the most favourable flow conditions, particularly by minimizing recirculation one millimetre and five millimetres away from the toe (0.26% and 0% of the cross-sectional area of the artery, respectively) and pressure drop (474.8 Pa), as well as the complete elimination of areas affected by pathologically high wall shear stress (WSS). The findings of this study point out the potential benefits of a smaller anastomosis angle on the performance and patency of bypass grafts through the minimization of pressure drop and areas affected by recirculation and abnormally high WSS.

#3215 RHE EFFECT OF ANASTOMOTIC ANGLE ON MATURATION OF AUTOGENOUS ARTERIOVENOUS FISTULA AFTER END-TO-SIDE ANASTOMOSIS OF CEPHALIC VEIN AND RADIAL ARTERY

Abstract Background and Aims Arteriovenous fistula (AVF) is the preferential choice of haemodialysis (HD) access, but failure of maturation of AVF is common. A previous French study had demonstrated reduced primary patency of radial-cephalic fistula with anastomotic angles &amp;lt; 30°. We have designed a study to determine if the angle of anastomosis affects the maturation of AVF in Chinese patients. Method We retrospectively studied our chronic patients who underwent the first cephalo-radial end-to-side anastomosis of AVF surgery at our Hospital from November 2019 to September 2022. All AVFs have been constructed by two of our dedicated nephrologists. The nephrologists performed the dissection and construction of the anastomosis according to the patient's anatomy. The angle of the anastomosis was not decided a priori and special care was given not to kink or twist the vein during the procedure. The AVF was defined as mature at 3 months if the blood flow was ≥ 500 ml/min and/or if the AVF was able to support adequate dialysis thrice a week. The patients were divided into two groups for evaluation using 45° of the AFV's anastomotic angles as cut-offs. The study has been approved by the local research and ethics committee. Statistics analysis: The IBM SPSS Statistics 26 software was used. The baseline characteristics of the two groups were analyzed using univariate analysis to find out if there was any statistical difference. The K-M curve was used to analyze if there was any statistical difference in AVF maturation between the two groups. Logistic regression was used to analyze the rate of maturation between the two groups, adjusted for confounding factors (including baseline characteristics and variables that have been shown as risk factors in previous studies, such as age, female gender, diabetes, preoperative vessel diameter, etc.), to determine whether the angle of anastomosis was an independent factor. Results A total of 159 Chinese patients were included in the study. The overall AVF maturation rate at 3 months was 93.08% (148/159 cases). Table 1 showed the patients’ baseline characteristics based on the AVF outcome. Table 2 showed the patients’ parameters in relation to different anastomotic angles (group 1: anastomotic angle ≤45°; group 2: &amp;gt;45°). The median time to AVF maturation of either group was 5 weeks (P = 0.9057, 95% CI 0.725-1.421) with no statistical difference. There was no statistical difference between the two groups in terms of age, gender, preoperative venous and arterial diameters, states of diabetes, coronary heart disease, peripheral vascular diseases, smoking, or biochemical parameters. Multivariate logistic regression analysis showed that there was no statistical difference between the two groups in AVF maturation rate at 3 months (OR = 0.976, 95% CI 0.273-3.489, P = 0.971). There was also no statistical difference after adjustment (OR = 0.863, 95% CI 0.231-3.233, P = 0.827). Conclusion This study has not established nor confirmed to any meaningful degree any relationship between the anastomotic angle using 45° as a cut-off and the maturation rate of AVF in Chinese patients at 3 months. Our overall AVF maturation rate was very high and none of the traditional risk factors for failed AVF nor the degree of anastomotic angle have any demonstrable effect on AVF maturation. The success might have been in part due to the skill and dedication of the nephrologists as operators. A prospective study involving a bigger patient group is necessary to further explore the effect of anastomotic angle on AVF maturation if any.

Effects of Anastomotic Angles and Distances of the Bypass Graft to the Stenosis on Blood Flow Hydrodynamics in a Bypass Grafting Coronary Artery

It is believed that the proper distance between the grafting location and the stenosis location and the appropriate angle of graft or transplantation in the blocked artery of the heart are two important factors in the removal or decrease of reappearance and re-development of intimal hyperplasia (IH), blood clotting, and re-blockage of the surgical artery. In the present study, a 3-D geometry of the host coronary artery as non-elastic with 75% symmetric axial cross-sectional area reduction is considered. The main assumptions were incompressible, laminar, steady-state, Newtonian, and non-Newtonian (with Herschel Bulkley model) blood flow. The 3-D Navier-Stokes equations coupled with the non-Newtonian constitutive model were solved numerically using a finite volume method with the procedure of the SIMPLE program. Shear stress distribution was obtained on the areas of potential re-obstruction and the occurrence of IH such as the Toe, Heel, arterial bed, suture location, and graft artery walls. Based on the results, the distribution of wall shear stress near the Heel, Toe location, and the intersection of the host and graft arteries suddenly increased dramatically. Wall shear stress (WSS) distribution was obtained in the areas of hyperplasticity re-incidence for some important anastomosis angles of grafted arteries, i.e. α=35°,45°,65°,75°. In addition, the increase in the angle of the graft artery caused a sharp increase in the shear stress on the area after the graft and the arterial bed in front of the branching region, and the shear stress decreases in the pre-graft region. Therefore, the excessive angle of the graft artery can cause damage to the arterial endothelial cells in the surrounding suture region.

Computational fluid dynamics investigation of effects of anastomosis angle on hemodynamic indicators in end-to-side brachioaxillary arteriovenous graft

Computational fluid dynamics investigation of effects of anastomosis angle on hemodynamic indicators in end-to-side brachioaxillary arteriovenous graft

Comparison of different anastomosis angles in radiocephalic fistula with modified functional end-to-side anastomosis

ObjectiveFunctional vein end to arterial side (ETS) anastomosis uses vein side to arterial side anastomosis with distal vein ligation, which is different from traditional ETS anastomosis. To date, there are no studies concerning different anastomotic angles of fistula with functional ETS anastomosis. The purpose of the study was to analyze the clinical outcomes concerning different anastomotic angles of functional ETS anastomosis in radiocephalic fistula.MethodsBetween January 2018 and December 2020, we performed a prospective cohort study concerning functional ETS anastomosis in radiocephalic fistula. According to vascular anatomy of patients, the anastomosis angles of fistula were designed at 30 ≤ angle ≤ 50°, 50 < angle ≤ 70°, and 135° smooth obtuse angle. The end points were the primary patency rate (PPR), the secondary patency rate (SPR) and the cumulative rate of reintervention (CRR) near anastomotic venous segment.Results124 patients with functional ETS anastomosiss were enrolled in this study. Pearson χ2 test showed that the group of 135°anastomosis angle had the maximum distance between arteries and veins, and the group of 30–50°anastomosis angle had the minimum distance between arteries and veins (P < 0.01). 30–50°anastomosis angle had the highest PPR at 12 months (P = 0.03) and the lowest CRR near anastomotic venous segment at 3 months (P = 0.04) and 12 months (P = 0.01). There were no significant differences among different anastomosis angles concerning the SPR within 12 months (P > 0.05). Kaplan–Meier and log-rank analysis showed that 30–50°anastomosis had the highest PPR (P = 0.03) and the lowest CRR near anastomotic venous segment (P = 0.01). A multivariable Cox model showed anastomotic angle was an independent factor predictive of the PPR (P = 0.04) and the CRR near anastomotic venous segment (P = 0.03). 50–70°anastomosis angle was a risk factor of decreasing PPR (P = 0.03). 50–70° (P = 0.01) and 135° (P = 0.03) anastomosis angle were both obvious risk factors of increasing CRR near anastomotic venous segment.Conclusion30–50°were the best anastomotic angles for functional ETS anastomosis, which had the highest PPR and lowest CRR near anastomotic venous segment.

Numerical Investigation of the Relationship between Anastomosis Angle and Hemodynamics in Ridged Spiral Flow Bypass Grafts

Bypass graft failures are linked to hemodynamic disturbances resulting from poor design. Several studies have tried to improve graft patency by modifying conventional graft designs. One strategy being employed is to induce spiral flow in bypass grafts using an internal ridge which has been proposed to optimize blood flow. However, there is still no study focusing on how the anastomosis angle can affect the hemodynamics of such a design despite its huge influence on local flow fields. To fill this gap, we aimed to understand and optimize the relationship between anastomosis angle and ridged spiral flow bypass graft hemodynamics to minimize disturbances and prolong graft patency. Steady-state, non-Newtonian computational fluid dynamics (CFD) analysis of a distal, end-to-side anastomosis between a ridged graft and idealized femoral artery was used to determine the anastomosis angle that would yield the least hemodynamic disturbances. Transient, pulsatile, non-Newtonian CFD analysis between a conventional and ridged graft at the optimal angle was performed to determine if such a design has an advantage over conventional designs. The results revealed that smaller anastomosis angles tend to optimize graft performance by the reduction in the pressure drop, recirculation, and areas in the host artery affected by abnormally high shear stresses. It was also confirmed that the modified design outperformed conventional bypass grafts due to the increased shear stress generated which is said to have atheroprotective benefits. The findings of the study may be taken into consideration in the design of bypass grafts to prevent their failure due to hemodynamic disturbances associated with conventional designs and highlight the importance of understanding and optimizing the relationship among different geometric properties in designing long-lasting bypass grafts.

Computational assessment of venous anastomosis angles and graft configurations in arteriovenous graft

Arterio-venous grafts are a viable option for hemodialysis as long-term vascular access. The leading cause of Arterio-venous Grafts (AVG) failure is the development of intimal hyperplasia (IH), primarily found in vessel areas with unfavorable hemodynamic conditions. Computational Fluid Dynamics (CFD) is utilized in this study to assess the effect of some geometrical designs at venous anastomosis on these conditions.At first, models with various anastomosis angles are designed. Results represent that the maximum Wall Shear Stress (WSS) in the model with the anastomosis angle of 15° has decreased from 34.07 Pa to 17.48 Pa (48.69%) compared to the conventional model. Moreover, vortices and regions with high WSS at vein anastomosis reduce remarkably.In the second part, to lessen the unfavorable hemodynamic conditions inspired by the rotational blood flow in the aorta, the graft is designed with several cross-sectional ridges to induce a swirl flow. Three essential hemodynamic parameters, including Oscillatory Shear Index (OSI), Time Averaged Wall Shear Stress (TAWSS), and Relative Residence Time (RRT) in pulsating blood flow models, are extracted, and the outcomes are compared to conventional AVG.Finally, according to the results of the previous sections, an optimized model is proposed. Comparing this model with the conventional one illustrates more than 90% decrement in regions related to high OSI values and a 22.84% reduction in RRT values as the main hemodynamic parameters to assess the areas with a high risk of IH development.

Quantitative Assessment of Aortic Hemodynamics for Varying Left Ventricular Assist Device Outflow Graft Angles and Flow Pulsation.

Left ventricular assist devices (LVADs) comprise a primary treatment choice for advanced heart failure patients. Treatment with LVAD is commonly associated with complications like stroke and gastro-intestinal (GI) bleeding, which adversely impacts treatment outcomes, and causes fatalities. The etiology and mechanisms of these complications can be linked to the fact that LVAD outflow jet leads to an altered state of hemodynamics in the aorta as compared to baseline flow driven by aortic jet during ventricular systole. Here, we present a framework for quantitative assessment of aortic hemodynamics in LVAD flows realistic human vasculature, with a focus on quantifying the differences between flow driven by LVAD jet and the physiological aortic jet when no LVAD is present. We model hemodynamics in the aortic arch proximal to the LVAD outflow graft, as well as in the abdominal aorta away from the LVAD region. We characterize hemodynamics using quantitative descriptors of flow velocity, stasis, helicity, vorticity and mixing, and wall shear stress. These are used on a set of 27 LVAD scenarios obtained by parametrically varying LVAD outflow graft anastomosis angles, and LVAD flow pulse modulation. Computed descriptors for each of these scenarios are compared against the baseline flow, and a detailed quantitative characterization of the altered state of hemodynamics due to LVAD operation (when compared to baseline aortic flow) is compiled. These are interpreted using a conceptual model for LVAD flow that distinguishes between flow originating from the LVAD outflow jet (and its impingement on the aorta wall), and flow originating from aortic jet during aortic valve opening in normal physiological state.

A Computational Analysis of the Influence of Anastomosis Angle on Stenosis-Prone Locations during Radio-Cephalic Arteriovenous Fistula Maturation

A Computational Analysis of the Influence of Anastomosis Angle on Stenosis-Prone Locations during Radio-Cephalic Arteriovenous Fistula Maturation

Prediction of the anastomosis angle of arteriovenous fistula in hemodialysis to standardize the surgical technique.

Arteriovenous fistula (AVF) is the preferred route of vascular access in hemodialysis. The primary reason of fistula failure is intimal hyperplasia (IH), which leads to stenosis. Wall shear stress (WSS) and disturbed flow are the critical parameters in the formation of IH. The primary goal of this study is to explore the influence of anastomosis angle on WSS and venous outflow rate, as well as to find the ideal angle of anastomosis for AVF to standardize surgical technique. Three-dimensional idealized geometries of end-to-side type AVF for the five various angles of anastomosis are considered in this study. The WSS, blood flow rate at the venous outlet for non-Newtonian, pulsatile blood flow are calculated using a numerical simulation technique. The WSS is higher at 75° compared to other angles and least at 45° for pulsating arterial inflows. The WSS is moderate at 30°, 60° and 90°. On the arterial bed and outer wall of the vein, immediately after the anastomosis, the recirculation zone is observed. At an angle of 45° and 90° anastomosis, the outflow rate is greater at distal venous end. If one believes that high wall shear stress causes IH within the AVF, the results suggest that the AVF should be formed at a 45° angle to avoid IH. However, if one believes that low wall shear stress causes IH within the AVF, the results suggest that AVF should be formed at either 30° or 75° to avoid IH. The findings spotlight the importance of anastomosis angle in determining AVF hemodynamics.

Vascular Factors Affecting Outcomes of Snuffbox AV Fistula with Side-to-Side Anastomosis: A Single Institutional Observational Study

Background: Angioaccess is considered the "Tendon of Achilles" for hemodialysis. Arteriovenous fistula (AVF) is the commonly entailed vascular access for hemodialysis. Objectives: The present study evaluates the outcomes of anatomical snuffbox AVF by preoperative and postoperative color Doppler scans. It also determines the anatomical snuffbox AVF maturation rate concerning preoperative radial artery diameter (RAD), cephalic vein diameter (CVD), cephalic vein distensibility, and peak systolic velocity (PSV). Methods: This study was conducted from April 2020 to January 2021 on end-stage renal diseases (ESRD) patients undergoing an operation for anatomical snuffbox AVF creation at our center after taking permission from the institutional ethics committee and written informed consent from patients. Results: Thirty-five ESRD patients underwent snuffbox arteriovenous fistula (SBAVF) creation, including 68% males and 32% females. Diabetes mellitus was noted in 40% and hypertension in 80%. Successful AVF maturation was noted in 92% (69.57% of males and 30.43% of females). The mean RAD assessed on color Doppler ultrasonography (CDUS) preoperatively was 1.79 mm, while the peak velocity of the radial artery at the snuffbox was 23.80 cm/s. Conclusions: We recommend applying the side-to-side configuration as its anastomosis angle is less owing to the lesser kink on the anastomotic site. A longer segment of anastomosis is achieved, and better fluid dynamics and WSS profiles are seen in this configuration with good outcomes.

Computational Study of Anastomosis Angle of Arteriovenous Fistula for Hemodialysis

Arteriovenous fistula (AVF) is the endorsed method of vascular access for hemodialysis in end-stage renal disease (ESRD). However, more than 60% of AVF fail to mature for hemodialysis. Intimal hyperplasia leads to stenosis is the primary cause of fistula failure. Wall shear stress (WSS) is one of the important parameters that enact a crucial role in building of intimal hyperplasia. The prime purpose of this research work is to investigate the effect of anastomosis angle on WSS, pressure drop, venous outflow rate and identify the optimal angle of anastomosis of AVF, so that it helps to standardize the surgical technique. In this research work, three-dimensional idealized geometries of end-to-side type AVF for the four different angles of anastomosis are created. Numerical simulation performed using incompressible, Newtonian blood to calculate the WSS, blood flow rate at the distal end of the vein and pressure drop across the anastomosis for the three arterial inflow 350, 500 and 900 ml/min. For all three arterial inflow, the WSS is high at 75° compared to other angles and it is less at 60°. The WSS at 45° and 90° are moderate. The venous outflow is increasing with the increase in arterial inflow condition for all anastomosis angles except for 45°. The outflow rate at distal venous end is highest, 344.85 ml/min at 45° for 500 ml/min arterial inflow. Pressure drop high at 45° and lowest at 90°. The intensity of disturbed flow and recirculation zone was observed at the area of anastomosis and it is high at 75°. From the results and observations, it can be concluded that 45° angle is the best choice for the anastomosis of AVF. This finding will standardize the surgical technique and subsequently, it will help to mature the AVF early and for a long time.