Restoration of wall shear stress in the cephalic vein during extreme hemodynamics

Cephalic arch stenosis: an analysis of outcome by type of first intervention

BACKGROUND

Cephalic arch stenoses (CAS) occur in near 70% of elbow arteriovenous fistulas. Percutaneous transluminal angioplasty (PTA) remains first-line treatment despite documented stent-grafts (SG) efficacy. The study aim is to report long-term outcomes based on initial treatment of CAS.

METHODS

Retrospective review of 12-year data in single tertiary centre. Outcomes included technical success, rupture rate, primary patency (PP), dialysis performance; categorical variables assessed via χ2 or Fisher's; nonparametric tests used for skewed data. Kaplan-Meier analysis used for PP and cumulative patency. Cox proportional hazard regression model to assess explanatory variables in PP.

RESULTS

One hundred one brachio- and radiocephalic fistulas with CAS were included. SG as first intervention had higher success than PTA (85% vs 61%, p = 0.003). Rupture occurred in 9/85 (10.6%) PTA vs 0% in SG (p = 0.046). In a subgroup with poor urea reduction rate (URR), both PTA and SG improved dialysis performance post-intervention (p = 0.002). SG demonstrated better PP than PTA (79,73,60% patency at 3, 6, 9 months; versus 71,51,47%; p = 0.195) and cumulative patency (73,61,61% at 1, 2, 3 years; versus 60,34,26%; p < 0.001). Of the variables analyzed, technical success of PTA was the only discriminating factor (coeff.-1.01; RR 35%, p = 0.035). Accesses that underwent secondary stenting performed better than primarily stented CAS (p = 0.01).

CONCLUSIONS

SG superiority is confirmed in CAS, particularly when angioplasty is unsuccessful. While PTA has short-lived benefits, it can improve dialysis performance. Other than higher success rate, primary CAS stenting did not have advantages compared to post-PTA stenting in our study. Other factors related to inflow, outflow, conduit characteristics are presumed to be involved in access longevity.

Computational Fluid Dynamics of Stent-Mounted Neural Interfaces in an Idealized Cerebral Venous Sinus. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2023;2023:1-4. [PMID: 38082814 DOI: 10.1109/embc40787.2023.10341099] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Hemodynamic changes in stented blood vessels play a critical role in stent-associated complications. The majority of work on the hemodynamics of stented blood vessels has focused on coronary arteries but not cerebral venous sinuses. With the emergence of endovascular electrophysiology, there is a growing interest in stenting cerebral blood vessels. We investigated the hemodynamic impact of a stent-mounted neural interface inside the cerebral venous sinus. The stent was virtually implanted into an idealized superior sagittal sinus (SSS) model. Local venous blood flow was simulated. Results showed that blood flow was altered by the stent, generating recirculation and low wall shear stress (WSS) around the device. However, the effect of the electrodes on blood flow was not prominent due to their small size. This is an early exploration of the hemodynamics of a stent-mounted neural interface. Future work will shed light on the key factors that influence blood flow and stenting outcomes.Clinical Relevance-The study investigates blood flow through a stent-based electrode array inside the cerebral venous sinus. The hemodynamic impact of the stent can provide insight into neointimal growth and thrombus formation.

Creating patient-specific vein models to characterize wall shear stress in hemodialysis population

End-Stage Renal Disease (ESRD) patients require arteriovenous fistulas (AVF) that allow a mature vein to withstand hemodialysis. Unfortunately, venous thrombosis and stenosis in the cephalic vein arch after AVF placement is common and heavily influenced by hemodynamics. To better assess forces and flow behavior in the cephalic arch, we have built patient-specific millifluidic models that allow us to explore the complex interplay between patient-specific vein geometry and fluctuating hemodynamics. These 3D models were created from patient-specific intravascular ultrasound and venogram images obtained three- and twelve-months post AVF creation and fabricated into soft elastomer-based millifluidic devices. Geometric validation of fabricated phantom millifluidic device shows successful replication of original computational 3D model. Millifluidic devices were perfused with a blood-mimicking fluid containing fluorescent tracer beads under steady-state physiologic cephalic vein flow conditions (20 mL/min). Particle image velocimetry was employed to calculate wall shear stress (WSS) across the cephalic arches. Experimental WSS profile evaluation reveals that the physiologic cephalic arch model yields WSS values within physiologic range [76–760 mPa]. Moreover, upon comparing WSS profiles across all models, it is noticeable that WSS values increase as vein diameter decreases, which further supports employed experimental and analysis strategy. The presented millifluidic devices show promise for experimental WSS characterization under pathologic flow conditions to contrast from calculated physiologic hemodynamics and better understand WSS influence on thrombosis and stenosis in hemodialysis patients.

Computational modeling of the cephalic arch predicts hemodynamic profiles in patients with brachiocephalic fistula access receiving hemodialysis

Background

The most common configuration for arteriovenous fistula is brachiocephalic which often develop cephalic arch stenosis leading to the need for numerous procedures to maintain access patency. The hemodynamics that contributes to the development of cephalic arch stenosis is incompletely understood given the inability to accurately determine shear stress in the cephalic arch. In the current investigation our aim was to determine pressure, velocity and wall shear stress profiles in the cephalic arch in 3D using computational modeling as tools to understand stenosis.

Methods

Five subjects with brachiocephalic fistula access had protocol labs, Doppler, venogram and intravascular ultrasound imaging performed at 3 and 12 months. 3D reconstructions of the cephalic arch were generated by combining intravascular ultrasounds and venograms. Standard finite element analysis software was used to simulate time dependent blood flow in the cephalic arch with velocity, pressure and wall shear stress profiles generated.

Results

Our models generated from imaging and flow measurements at 3 and 12 months offer snapshots of the patient’s cephalic arch at a precise time point, although the remodeling of the vessel downstream of an arteriovenous fistula in patients undergoing regular dialysis is a dynamic process that persists over long periods of time (~ 5 years). The velocity and pressure increase at the cephalic bend cause abnormal hemodynamics most prominent along the inner wall of the terminal cephalic arch. The topology of the cephalic arch is highly variable between subjects and predictive of pathologic stenosis at later time points.

Conclusions

Low flow velocity and wall pressure along the inner wall of the bend may provide possible nidus of endothelial activation that leads to stenosis and thrombosis. In addition, 3D modelling of the arch can indicate areas of stenosis that may be missed by venograms alone. Computational modeling reconstructed from 3D radiologic imaging and Doppler flow provides important insights into the hemodynamics of blood flow in arteriovenous fistula. This technique could be used in future studies to determine optimal flow to prevent endothelial damage for patients with arteriovenous fistula access.

A cohort study showing correspondence of low wall shear stress and cephalic arch stenosis in brachiocephalic arteriovenous fistula access

BACKGROUND

A brachiocephalic fistula is frequently placed for hemodialysis; unfortunately, cephalic arch stenosis commonly develops, leading to failure. We hypothesized that a contribution to brachiocephalic fistula failure is low wall shear stress resulting in neointimal hyperplasia leading to venous stenosis. The objective of this investigation is to determine correspondence of low wall shear stress and the development of cephalic arch stenosis.

METHODS

Forty subjects receiving hemodialysis with a primary brachiocephalic fistula access were followed from time of placement for 3 years or until cephalic arch stenosis. Venogram, Doppler, and viscosity were performed at time of fistula maturation, annually for 3 years or to time of cephalic arch stenosis. Computational hemodynamics modeling was performed to determine location and percent low wall shear stress in the arch. The relationship between wall shear stress at time of maturation and location of cephalic arch stenosis were estimated by correlating computational modeling and quadrant location of cephalic arch stenosis.

RESULTS

In total, 32 subjects developed cephalic arch stenosis with 26 displaying correspondence between location of low wall shear stress at time of maturation and subsequent cephalic arch stenosis, whereas 6 subjects did not (p = 0.0015). Most subjects with correspondence had low wall shear stress areas evident in greater than 20% of the arch (p = 0.0006). Low wall shear stress was associated with a higher risk of cephalic arch stenosis in the 23-to-45 age group (p = 0.0029).

CONCLUSIONS

The presence and magnitude of low wall shear stress in the cephalic arch is a factor associated with development of cephalic arch stenosis in patients with brachiocephalic fistula. Attenuation of low wall shear stress at time of maturation may help prevent the development of cephalic arch stenosis which is difficult to treat once it develops.