Key-words:
Combined technique - endovascular thrombectomy - stent clot retriever
Introduction
Mechanical thrombectomy is a widely used treatment in patients with acute ischemic
stroke. Recently, several companies have launched aspiration catheters and stent clot
retrievers of various sizes and characteristics. The fact that many combinations of
these devices and various techniques can be used,[[1]],[[2]],[[3]],[[4]],[[5]],[[6]],[[7]],[[8]],[[9]] may generate confusion among operators. Furthermore, which technique is better
suited for a quick approach using a single device or a secure recanalization using
multiple devices remains a controversial issue.
We used a stent-retrieving into an aspiration catheter with proximal balloon (ASAP)
technique as the first-line approach to manage patients with acute ischemic stroke
caused by occlusion of the anterior circulation.[[9]],[[10]] Through an accumulation of procedures, the ASAP technique has been improved gradually
based on the launching of new devices and the gleaning new knowledge from both clinical
and experimental data. Here, we report the modified ASAP technique that is used currently
at our institution. And our clinical results were compared with results that had been
reported using various techniques.
Materials and Methods
Patients
Patients with acute ischemic stroke were examined at admission to our institution
using the National Institutes of Health Stroke Scale (NIHSS).[[11]] Patients with an NIHSS score ≥4 were treatable by mechanical thrombectomy, and
computed tomography (CT) and magnetic resonance imaging were immediately performed.
Mechanical thrombectomy was performed in cases in which the presence of internal carotid
artery (ICA) or middle cerebral artery (MCA) occlusion was confirmed by magnetic resonance
angiography and intracranial hemorrhage was ruled out by CT. Patients who were treated
with mechanical thrombectomy at our institution between May 2019 and April 2020 were
included in the study. We performed a retrospective analysis of 30 consecutive cases
with acute ischemic stroke caused by occlusion of the anterior circulation who were
treated with the modified ASAP technique at our institution. Informed consent was
obtained after a certified neuroendovascular physician explained the content of treatment
and study to each patient or his/her family. This study was approved by the ethics
review board of our hospital (Application No.: 2020-083).
The preoperative patient characteristics, including age, sex, thrombus location, alberta
stroke program early CT score with diffusion-weighted magnetic resonance imaging (ASPECTS-DWI),[[12]] NIHSS score, and time from onset to puncture, as well as the postoperative thrombolysis
in cerebral infarction (TICI) score,[[13]] the number of passes necessary to achieve recanalization, time from puncture to
recanalization, procedural complications (including embolization to the new territories
and asymptomatic subarachnoid hemorrhage), and clinical outcome, were assessed. Successful
recanalization was defined as TICI score of 2B or 3 and good clinical outcome was
defined as a modified Rankin Scale (mRS) score of 0–2 at 3 months after the thrombectomy.
Protocol of the modified ASAP technique
All procedures were performed under local anesthesia via femoral puncture. A 9-F balloon-attached
guiding catheter was advanced into the proximal ICA of the affected side using a coaxial
5-F inner catheter. After an angiographic study, a 0.027-inch microcatheter with a
0.014-inch microguidewire was advanced through a large caliber aspiration catheter
(≥0.068-inch) in a triaxial fashion. In cases of distal MCA occlusion, we used a 0.021-inch
microcatheter. The tip of the microwire was shaped as a tiny pigtail; alternatively,
a preshaped type was used.[[14]],[[15]],[[16]] The advancement of the aspirator was stopped at the infra-clinoid portion of the
ICA. The proximal balloon was inflated before passage through the thrombus using the
microwire, to prevent distal migration of the thrombus. Simultaneous angiography through
both the microcatheter and the aspirator was performed, to document the exact position
of the thrombus. After the deployment of a stent retriever, the microcatheter was
not removed, which was in contrast with the original method of the ASAP technique
(Modification 1) [[Figure 1]]a. Continuous aspiration was initiated via the aspirator via connection to a mechanical
pump. The aspirator was advanced up to a position just proximal of the thrombus, to
accomplish contact aspiration, while the deployed stent was used as an anchor. In
cases with a second division of the MCA (M2), the aspirator was kept at the first
division of the MCA (M1). The stent and microcatheter were withdrawn into the aspirator
and completely removed from the entire system. Subsequently, the aspirator was withdrawn
until the fluid appeared to be continuously draining into the pump. This constituted
Modification 2 [[Figure 1]]b. Rather than removing the aspirator from the guiding catheter, we performed angiography
through the aspirator. If there was no residual clot, the balloon of the guiding catheter
was deflated. Cone-beam CT was performed before the guiding catheter was pulled out.{Figure
1}
Figure 1: (a) Schematic diagram of modification 1. After stent deployment, the microcatheter
is not removed from the entire system, in contrast with the original technique. The
aspiration catheter is advanced together with the microcatheter as the deployed stent
is used as an anchor. The tip of the aspirator is engaged at the proximal end of the
clot. (b) Schematic drawing of modification 2. The draining fluid from the aspirator
into the pump is usually stopped because of regional vasospasm, a wedge of the aspirator,
contact with a clot, or the sticking of a clot inside the aspirator. The aspirator
is slowly withdrawn until the fluid appears to continuously drain into the pump
Simple experimental evaluations
We evaluated the differences in the speed with which the mechanical pump (Penumbra
Inc., Alameda, CA, USA) aspirated water [[Figure 2]]A. First, the microcatheter was positioned to deploy the stent. After the stent
deployment, the microcatheter was withdrawn until the tail of the microcatheter reached
the same location as the tail of the stent delivery wire. The microcatheter was then
removed from the entire system, and the stent was removed from the aspiration catheter.
Using the indicator attached to the mechanical pump [[Figure 2]]B, we also evaluated the pressure at the tip of the aspirator with microcatheters
of various sizes and without the microcatheter: The 0.068-inch aspiration catheter
alone, the 0.0165-inch microcatheter inside the aspirator, the 0.021-inch microcatheter
inside the aspirator, and 0.027-inch microcatheter inside the aspirator.{Figure 2}
Figure 2: (A) Schematic drawing of the in vitro experiment. a: The position of the microcatheter
to deploy the stent. b: The microcatheter is withdrawn until the tail of the microcatheter
reaches the same location as the tail of the stent delivery wire. c: The microcatheter
is removed from the entire system. d: The stent is removed from the aspiration catheter.
(B) Photograph of the mechanical pump (Penumbra Inc., Alameda, CA, USA). a: The red
arrow indicates the pressure meter. b: The pressure at the tip of the aspirator was
evaluated by the presence or absence of the microcatheter
Results
A summary of the cases is provided in [[Table 1]]. The average age of the patients was 75.1 ± 10.1 (range, 43–91) years. Seventeen
out of the 30 participants were male (56.7%). The mean ASPECTS-DWI was 7.3 ± 2.0 (range,
2–10). The mean NIHSS score was 14.7 ± 6.4 (range, 5–29). The mean time from stroke
onset to puncture was 122.7 ± 37.8 (range, 60–210) min, except for two cases with
unknown stroke onset. A TICI score of 2B or 3 was achieved in 29/30 patients (96.7%).
The average number of passes was 1.2 ± 0.5 (range, 1–3). The mean time from puncture
to recanalization was 17.6 ± 6.84 (range, 9–39) min. One patient (3.3%) developed
minor subarachnoid hemorrhage postoperatively. Seventeen patients (56.6%) achieved
an mRS score of 0–1, whereas 23 patients (76.7%) achieved an mRS score of 0–2 at 3
months after the thrombectomy.{Table 1}
Table 1: Summary of the patients treated with modified aspiration catheter with a proximal
balloon technique in our institution
The results of the simple experimental evaluations are illustrated in [[Figure 3]]. When the microcatheter was removed from the entire system, aspiration became dramatically
faster. The pressure at the tip of the aspirator was not affected by the presence
or absence of the microcatheter.{Figure 3}
Figure 3: (A) Comparison of the speed of aspiration in various situations. a-d: The removal
of the microcatheter from the entire system© led to a dramatic increase in the speed
of aspiration. (B) Measurement of the pressure at the tip of the 0.068-inch aspiration
catheter. a-d: There were no significant differences between the presence or absence
of the microcatheter inside the aspirator
Discussion
Rationale of the modifications
Modification 1
In the original ASAP technique, the microcatheter was fully removed from the entire
system after the deployment of the stent.[[9]] This step was based on a simple experiment that evaluated the difference in the
time required to aspirate water into the aspirator [[Figure 3]]A. Therefore, we considered that the removal of the microcatheter increased the
flow velocity from the aspirator. However, we assumed that the contact aspiration
affected the degree of pressure at the tip of the aspirator, rather than the velocity
of the aspiration. We evaluated this pressure in various situations. The results are
shown in [[Figure 3]]B. The pressure at the tip of the aspirator was not affected by the presence or
absence of the microcatheter. Moreover, when the microcatheter was covered with the
proximal marker of the deployed stent, the stent could be retrieved easily into the
aspirator. The microcatheter worked to decrease the deflections of the flexible aspirator.
Modification 2
In the original ASAP technique, just after the stent and microcatheter were completely
removed from the entire system, the aspirator was also withdrawn and completely removed
from the guiding catheter out of the body.[[9]] We stopped the withdrawal of the aspirator until the fluid appeared to be continuously
draining into the pump [[Figure 1]]b. In almost all cases, continuous draining was confirmed when the tip of the aspirator
came back in the ICA, because of release from a wedge and/or a vasospasm. At that
position, we performed angiography via the aspirator. In cases of unsuccessful recanalization
or the presence of a residual clot, we thought that the second approach was able to
perform quickly via the remaining aspiration catheter. We used the remaining aspirator
as a distal access catheter, for quick re-access. This is one of the most advantageous
aspects of the use of the modified ASAP technique compared with the continuous aspiration
prior to intracranial vascular embolectomy (CAPTIVE),[[6]] stent retriever assisted vacuum-locked extraction (SAVE),[[7]] and aspiration-retriever technique for stroke (ARTS)[[8]] methods, in which both the stent retriever and the aspirator are retrieved as a
unit.
Comparison with other methods
There is no clear consensus regarding which technique is more effective for the first-line
attempt at mechanical thrombectomy. The representative techniques of mechanical thrombectomy
that have been reported are summarized in [[Table 2]]. Our modified ASAP technique yielded the best results regarding the number of passes,
the embolization to the new territory, the symptomatic intracranial hemorrhage, and
the mRS score at 3 months after the procedure.{Table 2}
Table 2: Summary of the results of the reported representative literatures
The simple stent-retrieving method has been widely used after a meta-analysis of five
trials demonstrated its benefits.[[17]] However, the simple stent-retrieving methods have some limitations, such as intracranial
hemorrhage caused by the vessel shift phenomenon. Conversely, some reports have recommended
a direct aspiration first pass technique (ADAPT)[[3]] for the first attempt. However, Delgado Almandoz et al.[[4]] reported that ADAPT was unsuccessful in approximately one-third of patients who
required salvage. Moreover, it was often challenging to navigate the currently available
large-caliber aspirators quickly into the distal cerebral arteries.
Several combination techniques using both an aspiration catheter and a stent retriever
have been reported. The so-called Solumbra techniques represent a method in which
there is no contact between the tip of the aspirator and the thrombus.[[4]],[[5]] Conversely, the CAPTIVE,[[6]] SAVE,[[7]] ARTS,[[8]] and ASAP[[9]] techniques are used for contact aspiration. In our modified ASAP technique, we
suggest that the large caliber aspiration catheter played an important role in the
highly successful recanalization rate. The deployed stent retriever works as a strong
anchor during the navigation of the large-caliber aspirator. Therefore, using our
technique, even the large bore aspirators could be navigated more smoothly than the
ADAPT. All seven cases in whom a REACT 71 aspiration catheter (Medtronic, Irvine,
CA, USA) was used in our series exhibited 1-pass recanalization with an average 12.1
± 1.8 (range, 9–15) min from puncture to recanalization.
Limitations
The present study had significant limitations, including the small initial experience
population, the retrospective and nonrandomized nature of the analysis, the absence
of a control group, and the involvement of a single institution. Self-adjudicated
results were also a limitation of our study. Therefore, the efficacy of the modified
ASAP technique may have been overestimated. Nonetheless, regardless of the lack of
statistical power, we believe that this case study will be of great interest to many
physicians and patients.
Conclusions
The findings of this study support the hypothesis that the modified ASAP technique
provides faster recanalization, fewer complications, and better clinical outcomes
compared with other techniques. A further large-scale study is necessary to evaluate
the efficacy of this preliminary study.
