Key-words:
Carotid artery stenting - filter protection device - thrombus
Introduction
Embolic protection devices (EPDs) are beneficial during carotid artery stenting (CAS).[[1]] Therefore, surgeons at most institutions select protection devices based on risk
factors, expected tolerance of the patients to flow cessation by temporarily clamping
the carotid artery, and plaque vulnerabilities. To avoid distal embolization of a
plaque during procedures, some authors have recently reported the efficacy of using
the combined protective method wherein a common carotid artery (CCA) balloon, an external
carotid artery (ECA) balloon, and an internal carotid artery (ICA) filter, with continuous
reversal flow to the femoral vein, are utilized.[[2]],[[3]],[[4]] Here, we present a case of CAS, wherein the combination of flow reversal method
and the distal filter was used. Moreover, a massive intraprocedural thrombus was found
in the filter device. Because the filter protection device is designed under the antegrade
flow condition, the manufacture and seller never consider such usage. The possible
causes of intraprocedural in-filter thrombus and the management of patients are discussed
to prevent subsequent catastrophic ischemic events.
Case Report
A 68-year-old male patient presented with frequent temporary right hemiparesis that
lasts for approximately 5 min. The patient had been taking medication for hypertension,
diabetes mellitus, and hyperlipidemia. The radiological examinations revealed 95%
stenosis of the origin of the left ICA [[Figure 1]]a. We have obtained a written informed consent from the patient. The patient was
prescribed 75 mg/day of clopidogrel and 200 mg/day of cilostazol for 2 weeks before
CAS. The patient underwent left CAS under local anesthesia.
Figure 1: (a) Preoperative lateral view of left carotid angiography showing 95% stenosis of
the origin of the internal carotid artery (white arrow). P: posterior. (b) Intraoperative
road-mapping image showing the universal protection method. Single arrow, balloon
in the external carotid artery; double arrows, balloon in the common carotid artery;
triple arrows, filter device in the internal carotid artery
A 4-Fr short sheath was first inserted into the right femoral vein prepared with the
flow reverse circulation. An 8-Fr short sheath was introduced into the right femoral
artery. Then, intravenous heparin was then administered to achieve an activated clotting
time (ACT) >250 s. An 8-Fr Cello balloon guiding catheter (Medtronic, Minneapolis,
MN, USA) was advanced into the left common carotid artery. A PercuSurge Guardwire
(200 cm; Medtronic) was navigated into ECA. When both balloons were inflated, reversal
flow was established from the distal ICA to the femoral vein through the guiding catheter.
Then, a Spider FX embolic protection device (Medtronic) was cautiously navigated to
the distal ICA through the stenotic lesion with Chikai 14 micro guidewire (Asahi Intecc,
Aichi, Japan) under road-mapping guidance [[Figure 1]]b. Although the retrograde flow was spontaneously collected, a massive newly developing
thrombus was found in the basket of the filter [[Figure 2]]. Because ACT was 288 s, we added 2000 U of heparin intravenously. After we waited
and observed the thrombus for 5 min, it became smaller and moved proximally out of
the filter and then, completely disappeared. ACT was 330 s at that time. Although
we checked the forced aspiration of the blood, there was no visible thrombus in the
collected blood. We decided to continue with the procedure. A prestenting balloon
(3.5 mm × 40 mm angioplasty balloon) was inflated at the stenotic lesion. A Carotid
WALLSTENT that was 8 mm × 21 mm in size (Boston Scientific, Natick, MA, USA) was then
used. Poststenting dilatation was performed at the narrowest area using a 4.5 mm ×
30 mm angioplasty balloon until nominal pressure was achieved. The filter was retrieved
under the reversal flow circulation. Then, both balloons were deflated. Complete carotid
reconstruction was achieved [[Figure 3]]a. Postoperative intracranial angiography showed no embolism [[Figure 3]]b. Magnetic resonance imaging on the postoperative day 1 showed no abnormal lesion
correlating to the procedure. The patient's postoperative course was uneventful, and
he was discharged from the hospital on the postoperative day 6.
Figure 2: Intraoperative lateral view of left carotid angiography showing in-filter thrombus
(white arrow head). The contrast medium was collected automatically from the guiding
catheter to the femoral vein through the external shunt
Figure 3: (a) Postoperative lateral view of left carotid angiography showing a complete reconstruction.
(b) Postoperative left intracranial carotid angiography showing no major arterial
thrombosis
Discussion
Since the introduction of CAS, the treatment options for carotid stenosis have changed.
CAS is increasingly utilized in patients with carotid artery stenosis.[[5]] Several EPDs are widely used. However, each device has its own disadvantages, which
limit the universal application of any device. Some authors have recently reported
the efficacy of the combined protective method that used a CCA balloon, an ECA balloon,
and an ICA filter, with continuous reversal flow to the femoral vein.[[2]],[[3]],[[4]] Goto et al. have reported that the incidence rate of both distal embolization and
unexpected intraprocedural complications was low when the combined protective method,
namely, the universal protection method (UPM) rather than other distal or proximal
protective methods are used.[[4]] We entirely agree with the efficacy of the UPM according to our experiences; however,
previous studies have not shown that the use of the filter device was not recommended.
The filter protection device is designed to restore the blood flow during procedures.
The filter works under the antegrade flow that is similar to a parachute. When the
parachute receives the retrograde flow, it must be collapsed. The filter protection
device may collapse under retrograde circulation. Because the filter protection device
is designed under the antegrade flow condition, the manufacture and seller never consider
such usage. [[Figure 4]] and [[Figure 5]] show in vitro experiments on the relationship between the filter device and flow
direction. When the direction of the fluid flow was antegrade, the filter showed enough
expansion. However, when the fluid flow was retrograde, the filter showed irregularly
shrinking. Indeed, the use of the filter device under the retrograde circulation is
contraindicated. These findings were more obvious with the FilterWire EZ (Boston Scientific,
Natick, MA, USA) of which design was a thin membrane than with the Spider FX of which
design was a fine net. This study has some limitations. First, current flow circulating
vascular model showed an approximately 20 cm/s flow velocity. We have to evaluate
under the precise flow condition of antegrade and retrograde, respectively. Second,
the viscosity of the fluid becomes another important factor for receiving the filter
device. Finally, computed fluid dynamics might be clear the turbulent flow pattern
around the filter device.
Figure 4: Photographs of the experiments with a FilterWire EZ. The arrows indicate the direction
of the fluid flow. (a) Under the antegrade flow, the filter showing enough expansion.
(b) Under the retrograde flow, the filter showing shrinking. The arrowheads indicate
a collapsed filter
Figure 5: Photographs of the experiments with a Spider FX. The arrows indicate the direction
of the fluid flow. (a) Under the antegrade flow, the ring showing enough expansion
and adapted. (b) Under the retrograde flow, the filter showing slightly elongated
In this case, when we confirmed the massive thrombus in the filter, we primarily chose
to perform an intensification of systemic heparinization rather than mechanical clot
retrieval. If the thrombus is retrieved through forced aspiration, other thrombus
might gush out from the filter one by one. Moreover, the massive thrombus may spill
over into ICA or the guiding catheter during the filter retrieval. The thrombus was
located only on the proximal side of the filter. If the patient's coagulability was
further promoted, the thrombus might advance to the distal side of the filter.
Although the in-filter thrombus was confirmed in this case, there was no complication
associated with the procedure. UPM can be safety used again. We recommend that the
filter protection device should be released and first retrieved under the flow reversal
circumstance with the two balloons because the thrombus might advance to the distal
side of the filter.
UPM is one of the most theoretical reliable protection methods during CAS; however,
physicians should be aware of the risk of developing intraprocedural thrombosis inside
the filter protection device. Because these devices are designed to work under antegrade
flow, they may not work well with the off-label usage. Thus, the filter protection
device should be first retrieved under the flow reversal circumstance to prevent the
distal migration of a clot around the filter device.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms.
In the form the patient(s) has/have given his/her/their consent for his/her/their
images and other clinical information to be reported in the journal. The patients
understand that their names and initials will not be published and due efforts will
be made to conceal their identity, but anonymity cannot be guaranteed.
