WSO - July 2023 - 690

690
International Journal of Stroke 18(6)
Introduction
Large vessel occlusion (LVO) strokes are most commonly
caused by either cardioembolism (CE), of which atrial
fibrillation (AF) is the most common risk factor, or large
artery atherosclerosis (LAA). AF and cardioembolic etiology
have been reported to be associated with larger infarcts
and poorer clinical outcomes,1-3 particularly prior to the
advent of endovascular thrombectomy (EVT).
The poorer outcome of AF may be related to collaterals.
Collateral flow plays an important role in acute ischemic
stroke. Two studies reported that stroke due to CE or AF
was associated with lower collateral score graded on computed
tomography angiography (CTA) and worse clinical
outcome at 3 months compared with stroke due to cervical
carotid atherosclerosis.4,5 Conversely, other studies failed
to show an association between AF and CTA collateral
score.6 The conflict findings indicate a more complex relationship
may exist between AF and collaterals.
Moreover, a recent study indicates that the worse stroke
outcome in AF may be explained by more severe hypoperfusion.2
The severe hypoperfusion on perfusion imaging
can reflect collateral function,7,8 whereas the CTA collateral
score is based on visualization of collateral vessel structure
of the occluded vascular territory. Indeed, the central function
of collateral flow is to maintain cerebral blood flow in
regions that are hypoperfused.8
Aim
In this study, we aimed to explore the complex relationship
between AF, collateral flow, and severe hypoperfusion in
patients treated with EVT.
Methods
Study design
This was a retrospective cohort study, selecting LVO
patients who received EVT. Patients were classified into
two groups: (1) AF group and (2) No AF group. The diagnosis
of AF was made when patient history was positive for
AF or when AF was diagnosed during hospital stay.
Patients
This study included patients who were enrolled in
INternational Stroke Perfusion REgistry (INSPIRE). Data
in this study were collected between 2011 and 2020 and
from 22 sites (9 Australian, 12 Chinese, and 1 Canadian).
This study obtained ethical approval from Hunter New
England Human Research Ethics Committee (11/08/17/4.01),
and informed consent was obtained for each patient for their
data to be used as part of the INSPIRE registry.
The key inclusion criterion was LVO patients who were
treated with EVT (with or without bridging thrombolysis).
International Journal of Stroke, 18(6)
Severe hypoperfusion volume
Severe hypoperfusion volume was defined as the region
with delay time > 6s on acute CTP.7 Hypoperfusion intensity
ratio was defined as the ratio of the severe hypoperfusion
volume of delay time >6 s divided by the volume of
tissue with delay time >2 s on acute CTP.7
Patient outcomes
The primary outcome was good functional outcome (defined
as mRS of 0-2 at 3 months post-stroke). Secondary outcomes
included: (1) 3-month mortality, (2) parenchymal hematoma
(PH), (3) parenchymal hematoma type 2 (PH2), (4) symptomatic
hemorrhagic transformation (sICH) according to the
safe implementation of thrombolysis in stroke-monitoring
study (SITS-MOST) criteria, and (5) recanalization assessed
on post-EVT angiography with a Modified Thrombolysis in
Cerebral Infarction score of 2b or 3.
Statistical analysis
All statistical analyses were done using STATA 13.0 (Stata
Corp, College Station, TX, USA), with confidence interval
(CI) set at 95% and alpha level set at 0.05. Continuous data
were summarized as median and inter-quartile range (IQR);
Exclusion criteria were incomplete data in INSPIRE
regarding the history (current or past) of AF, age, or
3-month modified Rankin Scale (mRS).
Imaging parameters
Baseline CT imaging included brain non-contrast CT, CT
perfusion (CTP), and CTA. The baseline CTP raw data
were centrally processed by commercial software MIStar
(Apollo Medical Imaging Technology, Melbourne, VIC,
Australia). A threshold of >3 s in delay time was used to
delineate the perfusion lesion, within which tissue with cerebral
blood flow ⩽30% was identified as an infarct core.9
Collateral
Collateral flow was assessed on baseline CTA using the
Miteff scale.10 Collateral status was graded as good, moderate,
or poor (Y.W. and C.C.) depending on the extent of contrast
visualized distal to the occlusion. The definition to
grade collateral status is as follows: poor collateral flow in
superficial vessels only, moderate collateral flow into the
Sylvian fissure, and good collateral flow up to the occlusion.
The Miteff scale was developed on grading middle cerebral
artery. In this study, we expanded the definition to grade
posterior circulation as follows: poor collateral flow in
superficial vessels only, good collateral flow up to the occlusion,
and moderate collateral flow in between.
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