Mechanical thrombectomy (MT) is an effective treatment for patients suffering from acute ischemic stroke secondary to large vessel occlusion. However, recanalization failure rates of interventions were about 20% in literature studies. We report our experience of unsuccessful MT with a focus on technical reasons.
From December 2010 to June 2021, six hundred eight patients with acute ischemic stroke due to large artery occlusion received MT using a stent retriever with or without an aspiration catheter in our institution. We divided the reasons for failure into six categories. We analyzed the reasons for failure by dividing our experience time into 3 periods.
A total of 608 cases of thrombectomy for large vessel occlusion were identified in the study period. The successful recanalization rate was 90.4%. In most of the cases (20/57, 35%), the thrombus persisted despite several passes, and the second most common cause was termination of the procedure even after partial recanalization (10/57, 18%). Similar proportions of in-stent occlusion, distal embolization, and termination due to vessel rupture were observed. On analysis of three periods, the successful recanalization rate improved over time.
MT fails due to various reasons, and intracranial artery stenosis is the main cause of MT failure. With the development of rescue techniques, the failure rate has gradually decreased. Further development of new devices and techniques could improve the recanalization rates.
Mechanical thrombectomy (MT) is a standard of care for acute ischemic stroke secondary to large vessel occlusion. Moreover, successful recanalization is an important factor for achieving the functional outcome. An increase in successful recanalization rates has improved stroke treatment and achieved a better outcome [
We retrospectively reviewed cases of failed MT over 10 years in a single institution. We also focused on the technical reasons for unsuccessful MT.
A retrospective study was performed in 608 patients with acute ischemic stroke due to large artery occlusion who received MT between December 2010 to June 2021. The following data were collected: patient age and sex, along with a history of diabetes mellitus, hypertension, atrial fibrillation, dyslipidemia, coronary artery disease, malignancy, and smoking. Data on the procedure time, number of passes, and angiographic findings were also collected. Dyslipidemia was defined as a total cholesterol score over 200 mg/dL or a triglyceride score over 150 mg/dL. The final reperfusion score was rated based on the modified thrombolysis in cerebral infarction (TICI) grading scale. Failure of recanalization was defined as a score of 0, 1, or 2a on the modified TICI scale.
We divided the reasons for failure into the following six categories: 1) Failure of clot retrieval, 2) Partial recanalization (TICI 2a), 3) In-stent occlusion, 4) Distal embolization, 5) Termination due to vessel rupture, and 6) Distal occlusion with high risk profile. Failure of clot retrieval indicated failure of recanalization of main large vessel occlusion due to no change in the clot despite several passes. Partial recanalization indicated failure to reach TICI grade IIb or III although some branch vessels were recanalized. In-stent occlusion was defined as cases of failure due to thrombus formation after intracranial stenting. Distal embolization indicated that the main occluded large vessel was recanalized, but the distal small vessel (e.g. the M3 or M4 segment) was still occluded by distal emboli. Termination due to vessel rupture was defined as end of the procedure because of occurrence of vessel rupture during intra-procedure angiography, no matter how overcame. Distal occlusion with high risk profile referred to cases of only angiogram since distal occlusion (e.g. P2 segment of the posterior cerebral artery) unlike brain CT angiography.
In addition, we analyzed the reasons for failure by dividing our experience time into 3 periods.
The period before the establishment of our institution’s protocol, before 2015, was called the pre-protocol period. The period of establishing the protocol was called the learning period and it ranged from 2016 to 2017 (
A total of 608 cases of thrombectomy due to large vessel occlusion were identified during the study period. Fifty-seven cases failed, and the successful recanalization rate was 90.4%. Demographic characteristics of patients with failed recanalization are presented in
During the whole period of MT, the most common reason for failure was difficulty of clot retrieval despite several passes (20/57, 35%). The second most common cause was termination of the procedure even after partial recanalization (10/57, 18%). Similar proportions of in-stent occlusion, distal embolization, and termination due to vessel rupture were observed (
On analysis of the three periods, the successful recanalization rate improved over time. The success rate in the pre-protocol period was 82% (118/143), and 88% of patients were successfully recanalized during the learning period (116/132). Recently, in the post-protocol period, only sixteen patients showed undesirable results (success rate of 95%, 328/344).
The main reason for each period was different. Failure of clot retrieval was the most common reason in the pre-protocol period (13/25, 52%). However, similar proportions of failure of clot retrieval (5/16, 31%), partial recanalization (5/16, 31%), and in-stent occlusion (4/16, 25%) were observed in the learning period. Unlike before, during the post-protocol period, termination due to vessel rupture was the main reason for failure (7/16, 44%) (
We analyzed the interventions from December 2010 to June 2021. During this period, we were able to confirm a successful recanalization rate of 90.4% in our institution. We analyzed in detail by the period, and we found that the successful recanalization rate was slightly increased during the learning period compared to the pre-protocol period. Also, the successful recanalization rate was increased by 7% from the learning period to the post-protocol period. As the protocol was established and the skill of the operator improved, the success rate increased dramatically.
Previously, Heider et al. published a categorized mechanism of unsuccessful thrombectomy. They reported that the main cause of thrombectomy failure was occlusion with peripheral ramifications (40%). Unlike in our study, which was the most common (35%) - not possible to make a proper comparison due to the different categories -, failure of clot retrieval was the second most common reason (25%). Compared with our report, they noted fewer cases of vessel rupture (3% vs 14%) [
The purpose of performing a review of failed cases is to overcome MT failure. We also tried to reduce failure in cases by using various methods and reported our experience. A history of thrombectomy can be called as a history of effort taken to decrease recanalization failure. To overcome refractory thrombectomy, several techniques and devices were published and developed. Recent advances in catheter technology have included very large, easily trackable, aspiration thrombectomy catheters that can more easily and reliably navigate the target vessel. Furthermore, the direct aspiration first pass technique (ADAPT) is a fast, simple, efficient, and safe strategy to achieve revascularization in patients with acute ischemic stroke secondary to large vessel occlusion [
Intracranial atherosclerotic stenosis could be the most common cause of refractory occlusion after MT in patients with acute ischemic stroke. Several previous studies have reported outstanding procedural and clinical outcomes of stent angioplasty using self-expanding stents [
To avoid parent artery rupture, more studies are needed to reduce vessel wall injury. It is necessary to understand the device and the changes in hemodynamic effects after the procedure. Vessel wall injury affects not only the outer diameter of the stent retriever but also the total radial force of the devices during the procedure [
Urgent bypass surgery may also be an optional treatment for refractory occlusion. It has been reported that urgent bypass can prevent expansion of infarction and improve the clinical and radiological outcomes in highly selected patients [
A comparison of failed cases with successful cases to evaluate the factors associated with failure was not performed. The study cohort was relatively small because it included patients at a single institution. Another limitation is that the study design was a retrospective review of case series.
There are various reasons for thrombectomy failure and we are overcoming them through multiple methods. Recently, vessel rupture has been the most common cause of thrombectomy failure in our institution, and more studies are needed to reduce vessel wall injury.
The development of new devices and techniques will also help reduce thrombectomy failure.
Finally, urgent bypass surgery may be an optional treatment for cases of thrombectomy failure.
The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.
Flowchart of the ‘‘Stroke Code’’ Protocol. ER, emergency room; CT, computed tomography; tPA, tissue plasminogen activator; LS, Long Sheath; ADAPT, a direct aspiration first pass technique
Demographic characteristics of failed cases
Cases of failure (n=57) | |
---|---|
Mean age, y | 71.46±12.21 |
Female sex, n (%) | 29 (50.9%) |
HTN, n (%) | 42 (73.7%) |
DM, n (%) | 16 (28.1%) |
Atrial fibrillation, n (%) | 19 (33.3%) |
Dyslipidemia, n (%) | 29 (50.9%) |
CAD, n (%) | 3 (5.3%) |
Malignancy, n (%) | 5 (8.8%) |
Smoking, n (%) | 18 (31.6%) |
Left hemisphere stroke, n (%) | 29 (50.9%) |
Posterior circulation stroke, n (%) | 5 (8.8%) |
Tissue-plasminogen activator, n (%) | 12 (21.1%) |
Initial NIHSS (mean value) | 11.16 (2−24) |
NIHSS, National Institutes of Health Stroke Scale
Radiologic and clinical outcomes
Cases of failure (n=57) | |
---|---|
Procedure time (mean value, mins) | 138.1 (20−313) |
Number of passes (mean value) | 3.84 (1-10) |
Partial recanalization (mTICI 2a), n (%) | 29 (50.9%) |
Functional independency (3 month mRS ≤2), n (%) | 8 (14%) |
Mortality, n (%) | 16 (28.1%) |
TICI, thrombolysis in cerebral ischemia; mRS, modified Rankin Scale
Reason of failure in whole period
No. (%) | |
---|---|
Fail of clot retrieval | 20 (35%) |
Partial recanalization | 10 (18%) |
In-stent occlusion | 8 (14%) |
Distal embolization | 9 (16%) |
Termination due to vessel rupture | 8 (14%) |
Distal occlusion with high risk profile | 2 (3%) |
Reason of failure in each periods
Pre-protocol P. No. (% of 25) | Learning P. No. (% of 16) | Post-protocol P. No. (% of 16) | |
---|---|---|---|
Fail of clot retrieval | 13 (52%) | 5 (31%) | 2 (12%) |
Partial recanalization | 2 (8%) | 5 (31%) | 3 (19%) |
In-stent occlusion | 3 (12%) | 4 (25%) | 1 (6%) |
Distal embolization | 7 (28%) | 0 (0%) | 2 (12%) |
Termination due to vessel rupture | 0 (0%) | 1 (6%) | 7 (44%) |
Distal occlusion with high risk profile | 0 (0%) | 1 (6%) | 1 (6%) |