The Potential use of 3-D Ultrasound for Arteriovenous Fistula

Flow Dynamics Assessment

Eoin A Murphy1, Rose A Ross2, Shona Z Matthew1,

and John Graeme Houston1

This project has received funding

from the European Union’s Seventh

Framework Programme for research,

technological development and

demonstration under grant

agreement no 324487.

1Division of Cardiovascular and Diabetes Medicine, School of Medicine, Ninewells Hospital, Dundee, DD1 9SY.

2 NHS Tayside Vascular Department, Ninewells Hospital, DD1 9SY, UK.

Image References

[1] T. Vachharajani, Atlas of dialysis vascular access, School of Medicine. Wake Forest. Univ. (2010).

[2] A. Brahmbhatt, A. Remuzzi, M. Franzoni, S. Misra, The molecular mechanisms of hemodialysis vascular access failure, Kidney Int. 89 (2016) 303–316.

doi:10.1016/j.kint.2015.12.019.

Introduction Haemodialysis is the most common treatment for end stage renal

disease. An arteriovenous fistula (AVF) is considered the preferred

vascular access needed for haemodialysis, although, up to 50% fail

to mature. One theory as to why AVFs fail to mature is adverse local

haemodynamics. To study the local haemodynamics computational

fluid dynamics (CFD) is used. 3-D ultrasound could potentially pro-

vide a cheap and accessible means to generate the patient-specific

geometries needed for this study.

The ReDVA Project— Combat the problem of renal dialysis

vascular access failure

Goals – Develop clinical technologies and methodologies that improve long-term performance of VA techniques

– Knowledge exchange

AVF Creation

Fistula surgically created by joining an artery to a vein.

One commonly used fistula type is a radiocephalic (radial

artery and cephalic vein).

Radiocephalic Fistula [1]

AVF Failure—Get with the Flow

Local non-physiological haemodynamics

within a fistula are theorised to encourage

intimal hyperplasia, causing fistula failure.

(a) Unidirectional WSS—physiological

(b) Disturbed WSS—non-physiological

Wall Shear Stress (WSS) and

Endothelial Cells (ECs)

ECs sense the local haemodynamics and

release mitogens and cytokines that regu-

late the proliferation and migration of cells

into and within the vessel wall, as shown

in figure on the right.[2]

CFD Analysis of AVFs

Biological processes within fistula occur at very small scale and cur-

rently unable to get an accurate view of local haemodynamics in vi-

vo.

Therefore, CFD software used to model and assess the haemody-

namics within patient-specific AVFs.

Geometries of patients’ AVFs needed for CFD currently acquired us-

ing magnetic resonance imaging (MRI) at five time-points:

pre-surgery, and post-surgery at 2-4 weeks, 4-6 weeks, 6-8 weeks

and 6 months

Problems

MRI Problems: expensive and time-consuming

Patient Problems: difficult for renal patients to commit to five

extra hospital visits (in addition to dialysis sessions) for MRI scan-

ning, some potential patients find MRI claustrophobic, frailty of pa-

tients (difficult to lie still for one hour).

Geometry Problems: loss of signal around fistula region; therefore,

geometry difficult to acquire in specific region of interest.

Solution—Ultrasound

Ultrasound is already used to assess renal patients pre-surgery, and post-surgery at

regular intervals in Ninewells. 3-D ultrasound could offer a viable alternative to MRI

for patient AVF geometry acquisition. Advantages: no additional patient visits are

needed, assessment is non-invasive, accessible, cheap, good resolution is attainable,

flow measurements can be acquired, and 3-D geometries can be attained.

Sample

Ultrasound

Images

Doppler Ultrasound showing

disturbed flow in fistula

Ultrasound image of fistula with

velocity profile over cardiac cycle

Email: Eoin A Murphy—etmurphy@dundee.ac.uk

Foreseeable Issues

Ultrasound is operator dependent. Also, specific ultrasound machine needed capable

of 3-D image acquisition, and position and orientation of images need to be known.