A pilot study on the cause of recurring cerebral thrombo-embolic events after Branched Thoracic Endovascular Aneurysm Repair

With high rates of stroke after fenestrated or branched TEVAR, it is crucial to
investigate the cause of cerebral thrombo-embolic events to reduce the risk of
complications after TEVAR surgery. It has been hypothesised that deformation of
stentgrafts occurs by stentgraft rings moving closer together, which causes the
fabric in between the rings to fold inwards (concertina-effect). Regions of
reduced or stagnating blood flow - causing red blood cells to remain at certain
locations with a higher residence time - and increased fluid shear stress could
occur in the folds. These two hemodynamic changes combined will promote
platelet activation, which could contribute to thrombus formation in
stentgraft limbs. However, the relation between these blood flow patterns,
stentgraft deformation patterns and stroke rates after a (branched)TEVAR
treatment still remains unknown.

The first step towards understanding strokes after bTEVAR is to investigate
blood flow patterns in patients who suffered from such complications after
implantation of a Relay ® Branch stentgraft (Terumo Aortic, Vascutec Ltd,
Inchinnan, UK). The patient population that fits this description is relatively
small and we are still uncertain about whether the blood flow patterns can be
measured in these patients, along with the quantification of the parameters we
are interested in. That is why a logistical pilot will be performed on one
patient. The aim of this pilot is to develop a workflow for investigating blood
flow in the aortic arch and carotid arteries of such a patient using two
imaging modalities. With this, we can investigate if it is possible to measure
the parameters that we hypothesize- in combination with clinical outcome - are
able to give crucial information about which flow patterns are deemed
favourable or unfavourable regarding the formation of thrombus and
thrombo-embolic events.

The blood flow patterns will be investigated using two different imaging
modalities. The first method is phase-contrasted four-dimensional magnetic
resonance imaging (4D-flow MRI), to be applied to image broad blood flow
direction and velocity in the aortic arch and branches. The second method is
using blood Speckle Tracking (bST), a high frame-rate echography technique used
to image high resolution blood flow patterns, to be applied in the carotid
arteries. Blood flow will be investigated using parameters such as stagnating
or recirculation blood flow patterns, flow velocity and wall shear stress.
Hypothetically, certain unfavourable flow patterns in the aortic arch and/or
the carotid arteries will be observed in the patient who suffered
complications. In the future , these patterns can be compared to those in
healthy volunteers to gain insights into which blood flow patterns could
contribute to thrombo-embolic events after (b)TEVAR.

This data collection will lead to a broader *Stented Vascular Triplet* project,
in which besides analysing the in-vivo scans, in-vitro (physical phantom
fabrication) and in-silico modelling (computational fluid dynamics) will be
performed. These models and additional imaging experiments will give even more
detailed flow and stentgraft deformation information. This will aid
understanding and prevention of complications after (branched)TEVAR surgery by
for example optimising stentgraft design in the future.

This is a pilot study for investigating the cause of recurring cerebral
thrombo-embolic events in a patient after (branched) TEVAR surgery. The main
aim of this logistical pilot is to develop a workflow for investigating blood
flow patterns in such a patient using two imaging modalities. With this, we can
investigate if it is possible to measure the parameters that we hypothesize- in
combination with clinical outcome - are able to give crucial information about
which flow patterns are deemed favourable or unfavourable regarding the
formation of thrombus and thrombo-embolic events.

Blood flow patterns - a combination of anatomy, blood flow velocity, direction
- and quantitative parameters such as wall shear stress in the stented region
of the aorta and carotid arteries leading to the brain using 4D-flow MRI and
blood Speckle Tracking. Comparison of results to those of healthy volunteers in
the future will gain insights into which of the observed patterns contribute to
thrombus formation after bTEVAR.

This observational study will be performed in one patient from the Medisch
Spectrum Twente (MST) hospital in Enschede, the Netherlands.

The present study carries no risks for the participant. Blood Speckle Tracking
and 4D-flow MRI are safe diagnostic procedures. The patient included in this
study will visit both the University of Twente and the Rijnstate hospital, so
it will take up some of their time (both visits will take approximately 1.5
hours)

This research might benefit the patient with complications after bTEVAR to gain
insights into why the recurring strokes events occurred, depending on the
outcomes. The outcomes will also give rise to more advanced in-vitro or
in-silico research in the future.