The effect of anastomotic angle and diameter ratio on flow field in the distal end-to-side anastomosis

Flow fields in the distal end-to-side anastomosis of coronary artery bypass graft are associated with intimal hyperplasia and bypass failure. This work aims to demonstrate the effect of anastomotic angle and diameter ratio on flow field of coronary artery bypass graft. The flow fields inside polydimethylsiloxane models of coronary artery bypass graft with various anastomotic angles ( α = 30°, 45°, 60° and 75°) and different diameter ratios ( Φ = 0.78 and 1.11) are investigated using particle image velocimetry and computational fluid dynamics method under pulsatile flow condition. The results show that the anastomotic angle is positively correlated with the number and area of the recirculation zone, and the flow field disturbance at the anastomosis will develop in the same direction. Compared with that of Φ = 0.78, when Φ = 1.11, the flow fields at the anastomosis are relatively smoother with less turbulence.

Effect of Anastomotic Angle on Pressure Drop in Arteriovenous Fistulae

The amount of the blood flow rate to an arteriovenous fistula (AVF) is one of the primary factors that determine the likelihood of maturation. The increase in the flow rate is dependent on the amount of the resistive forces in the AVF which can be evaluated by pressure drop (Δ p). Our group has shown that the surgical configuration of AVF affects the hemodynamics and thus the remodeling within the AVF. Here, our aim is to study the effect of AVF configuration on the induced Δ p. Based on the data collected in our previous in-vivo porcine experiments, idealized models of AVFs with anastomosis angles of 30°, 60°, and 90° were created and numerically solved to find Δ p under steady-state conditions. The Δ p from the idealized models were within the same range as the experimental data (15.31 ± 3.78 mmHg). The highest and lowest Δ p were found to be 14.75 and 6.40 mmHg for the 30° and 90° AVFs, respectively. Moreover, an inverse relationship was found between the Dean number ( De) and Δ p. As De decreased with increasing radius of curvature (from higher anastomotic angles to the lower), the Δ p increased. These data suggest that creating the AVFs in a surgical configuration that results in larger De (lower radius of curvature such as 90° AVF) may achieve higher flow rate due to relatively lower Δ p. In contrast, creation of AVF with lower De which represents a sharp bend with high radius of curvature (30° AVF) could be detrimental to AVF maturation as it results in relatively higher Δ p.

Prosthetic Arteriovenous Grafts for Hemodialysis

Introduction Prosthetic arteriovenous (AV) grafts are indicated in patients with failed AV fistula (AVF), exhausted superficial veins or unsuitable vessels. Increasing the proportion of prevalent hemodialysis (HD) patients using autogenous AVF should reduce the need for AV grafts and associated morbidity. This paper reviews the current role of prosthetic AV grafts in vascular access for HD. Technical considerations Prior to the insertion of a prosthetic AV graft, a comprehensive review of previous access procedures and full physical examination in addition to vessel mapping is required. Anastomotic technique should take into account the flow diffuser concept, graft geometry and an anastomotic angle of 15° in order to reduce the incidence of intimal hyperplasia. Results Many authors report 1 and 2-yr cumulative graft patency rates of 59–90% and 50–82%, respectively. The major drawbacks with synthetic grafts include: thrombosis, a five-fold increase in infection risk and steal syndrome. The choice between surgical and percutaneous methods of dealing with blocked AV grafts remains controversial, though percutaneous techniques are assuming an increasingly important role. Percutaneous strategies are successful in declotting access in 67–95% of cases. Stenting of stenotic lesions following thrombectomy improves secondary patency rates. Strategies for dealing with AV graft infection include antibiotic prophylaxis, partial, subtotal or total graft excision and the use of biological prosthesis. Conclusions Though more prone to complications than autogenous AVFs, AV grafts offer a short maturation period and are more amenable to thrombectomy by radiological or surgical means. Complex AV grafts may be appropriate in patients with exhausted access sites.

Particle image velocimetry measurements of three proximal anastomosis models under a pulsatile flow condition

This study was designed to examine the effects of the anastomotic angle on the flow and haemodynamic parameter distribution patterns of the proximal anastomoses, with emphasis on identifying site-specific haemodynamic features that could reasonably be expected to trigger the initiation and further development of anastomotic intimal hyperplasia. Particle image velocimetry measurements were carried out with three simplified glass proximal models under a physiological flow condition. The results revealed that the disturbed flow and the induced shear stress patterns including low recirculation flow, stagnation point, high wall shear stress, high temporal wall shear stress gradient, low time-averaged wall shear stress (TAWSS), and high oscillating shear index (OSI) occurred around the anastomotic joints and the flow field at proximal anastomosis was strongly affected by the anastomotic angle. Among the three models investigated, the 45° backward anastomosis is found to have a smaller low-recirculation-flow region along the graft inner wall, non-stationary stagnation, and separation points, a higher TAWSS and smaller high-OSI low-TAWSS and low-OSI high-TAWSS regions.