Article Text

First-line thrombectomy strategy for distal and medium vessel occlusions: a systematic review
  1. Cem Bilgin1,
  2. Nicole Hardy2,
  3. Kristen Hutchison2,
  4. John Michael Pederson2,3,
  5. Alexander Mebane3,
  6. Peace Olaniran2,
  7. Hassan Kobeissi4,
  8. Kevin M Kallmes2,
  9. David Fiorella5,
  10. David F Kallmes1,
  11. Waleed Brinjikji1
  1. 1 Department of Radiology, Mayo Clinic, Rochester, Minnesota, USA
  2. 2 Nested Knowledge, Inc, Saint Paul, Minnesota, USA
  3. 3 Superior Medical Experts, Inc, St. Paul, Minnesota, USA
  4. 4 Central Michigan University College of Medicine, Mount Pleasant, Michigan, USA
  5. 5 Department of Neurosurgery, Stony Brook University, Stony Brook, New York, USA
  1. Correspondence to Dr Cem Bilgin, Department of Radiology, Mayo Clinic, Rochester, Minnesota, USA; bilgin.cem{at}mayo.edu

Abstract

Background The benefit of mechanical thrombectomy (MT) and efficacy of different first-line MT techniques remain unclear for distal and medium vessel occlusions (DMVOs). In this systematic review, we aimed to compare the performance of three first-line MT techniques in DMVOs.

Methods The PubMed database was searched for studies examining the utility of MT in DMVOs (middle cerebral artery M2-3-4, anterior cerebral artery, and posterior cerebral artery). Studies providing data for aspiration thrombectomy (ASP), stent retriever thrombectomy (SR), and combined SR+ASP technique were included. Non-comparative studies were excluded. Safety and efficacy data were collected for each technique. The Nested Knowledge AutoLit platform was utilized for literature search, screening, and data extraction. Pooled data were presented as descriptive statistics.

Results 13 studies comprising 2422 MT procedures were identified. The overall successful recanalization rate was 77.0% (1513/1964) for DMVOs. SR+ASP had a successful recanalization rate of 83.7% (297/355), SR had a 75.6% rate (638/844), while ASP alone had a 74.2% rate (386/520). The overall functional independence rate was 51.3% (851/1659) among DMVOs. The ASP alone group had a functional independence rate of 46.9% (219/467), while functional independence rates of the SR and SR+ASP groups were 51.5% (372/723) and 61.7% (174/282), respectively. Finally, the subarachnoid hemorrhage rates were 1.8% (4/217) for the ASP group, 9.3% (26/281) for the SR group, and 11.9% (41/344) for the SR+ASP group.

Conclusions Our systematic review supports the proposition that MT is a safe and effective treatment option for DMVOs. Additionally, while the SR+ASP group had consistently high rates of clot clearance and good neurological outcomes, the SR and SR+ASP groups also had higher rates of subarachnoid hemorrhage, highlighting the need for improved DMVO treatment devices.

  • thrombectomy
  • stroke

Data availability statement

Data are available upon reasonable request. The data supporting the findings of this study are available upon reasonable request.

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WHAT IS ALREADY KNOWN ON THIS TOPIC

  • Growing evidence supports the safety and efficacy of mechanical thrombectomy (MT) in distal and medium vessel occlusions (DMVO); however, the performance of first-line MT techniques remains unclear for DMVOs.

WHAT THIS STUDY ADDS

  • This systematic review of comparative studies provides good quality evidence on the performance of first-line MT techniques. Also, our review indicates that outcomes of MT might change with the first-line thrombectomy technique.

HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE, OR POLICY

  • Thrombectomy devices that were primarily designed for proximal vessel occlusions may not be highly effective in DMVO. Therefore, this review underlines the need for improved thrombectomy devices for DMVOs.

Introduction

Several randomized clinical trials (RCTs) have established the utility of mechanical thrombectomy (MT) in proximal large vessel occlusions (PLVOs).1–5 However, distal and medium vessel occlusions (DMVOs) were either underrepresented or were completely excluded from these pivotal trials, despite constituting 25–40% of acute ischemic strokes.6 As a result, clinical evidence for endovascular treatment of DMVOs is still sparse.

Even though DMVOs lead to smaller core infarct volume, occlusion of an artery supplying eloquent areas can still result in severe neurologic deficits and significantly affect patients’ quality of life. Current guidelines recommend intravenous thrombolysis (IVT) over MT in DMVOs due to more robust clinical evidence (class 1 vs class 2b).6 However, IVT fails to achieve successful recanalization in 50% of DMVOs.7–9 Additionally, secondary DMVOs may occur in patients who have already received IVT. Therefore, there has been a growing interest in the potential role of the MT in DMVOs.

The recent introduction of new generation small-caliber catheters and low-profile stent retrievers have allowed access to the distal occlusion site. However, a longer and tortuous access route is not the only problem for DMVOs. Distal and medium intracranial vessels also have a smaller caliber and thinner arterial walls compared with proximal intracranial arteries.8–10 Therefore, in addition to recanalization performance, safety is also an important concern in the selection of a first-line thrombectomy strategy for DMVOs.

Pivotal RCTs have proved that aspiration and stent retriever techniques are safe and equally effective for PLVOs.11 12 However, in contrast to PLVOs, the data on the performance of first-line thrombectomy techniques are less robust for DMVOs. Current literature on DMVOs mostly consists of single artery- or device-oriented observational studies, and unfortunately, no RCT is available. Therefore, in this systematic review, we aimed to assess the performance of three main first-line thrombectomy techniques for DMVOs.

Methods

Literature search

This systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.13 We systematically searched PubMed using the following search strings:

  1. ((‘ischemic stroke’ OR ‘ischaemic stroke’ OR AIS OR (clot AND stroke)) AND (A2 OR PICA OR M3 OR M2 OR distal) NOT (m1)) AND ((stent-triever OR stentriever OR stenttriever OR ‘stent retriever’ OR aspiration OR DAC OR ‘distal access catheter’ OR ADAPT OR thrombectomy OR embolectomy)) AND ((FPE OR ‘first pass effect’ OR ‘first pass efficacy’ OR mRS OR ‘modified Rankin Scale’ OR TICI OR ‘thrombolysis in cerebral infarction’ OR sICH OR hemorrhage OR haemorrhage))

  2. ((ischemic stroke OR AIS) AND (A2 OR PICA OR M3 OR M2 OR distal OR A1 OR A3 OR PCA) NOT (m1)) AND ((stent-triever OR aspiration OR thrombectomy)) AND ((FPE OR mRS OR TICI OR sICH OR hemorrhage OR mortality))

  3. ((ischemic stroke OR AIS) AND (A2 OR PICA OR M3 OR M2 OR distal) NOT (m1)) AND ((stent-triever OR aspiration OR thrombectomy)) AND ((FPE OR mRS OR TICI OR sICH OR hemorrhage)).

Additionally, we contacted experts in the field for relevant articles and updated our search results according to their feedback.

Eligibility criteria and study selection

We included all original comparative studies providing data for the endovascular treatment of DMVOs (middle cerebral artery M2-3-4, anterior cerebral artery (ACA), and posterior cerebral artery (PCA)). No limitation on publication year was applied, and all publications up to July 25, 2022 were screened. Exclusion criteria consisted of (1) non-comparative studies, (2) non-original studies (review articles, editorials, video reports, correspondence papers), (3) in vitro and ex vivo studies, (4) in vivo animal studies, (5) papers focused on tandem occlusions, (6) case series, (7) studies not providing detailed occlusion location data, and (8) articles not written in English language.

Data extraction and study outcomes

The AutoLit platform was utilized for literature searching, screening, and data extraction. One author (KH) performed data extraction, and another three authors (NH, CB, AM) further checked the extracted data for accuracy. Investigated first-line strategies were aspiration thrombectomy (ASP), stent retriever thrombectomy (SR), and combined stent retriever+aspiration technique (SR+ASP). For each treatment strategy and overall study cohort, baseline patient characteristics were collected, including age, thrombus location, and IVT utilization data. Additionally, safety and efficacy outcomes of first-line treatment techniques were collected, including successful recanalization (Thrombolysis In Cerebral Infarction scale, TICI ≥2b), complete recanalization (TICI 3), functional independence (modified Rankin Scale (mRS) 0–2 at 90 days), symptomatic intracranial hemorrhage (sICH), subarachnoid hemorrhage (SAH), first-pass efficacy (TICI ≥2b), and distal embolization data. Due to the limited number of comparative studies, considerable heterogeneity in study designs and patient characteristics, and relatively high risk of bias among the included studies, meta-analysis was not performed.

Risk of bias

The risk of bias associated with each study was scored using the Risk Of Bias In Non-randomized Studies–of Interventions (ROBINS-I) tool.14 In brief, the risk of bias form included 50 questions relating to seven different domains of study bias, including bias due to confounding, selection of participants, classification of interventions, deviations from intended interventions, missing data, measurement of outcomes, and selection of reported results. The risk of bias assessment was completed independently by two reviewers (HK, PO). Any disagreements were discussed and resolved by a third reviewer (JMP). The risk of bias of each study was rated as low, moderate, serious, or critical at the discretion of the third author, and with discussion between the two independent reviewers. After performing the risk of bias assessment, we generated a ‘traffic light plot’ and an risk of bias summary plot using the ‘robvis’ package for R.15

Results

Search results and study characteristics

We identified 295 potentially relevant papers with the initial PubMed database search and expert recommendations, of which 13 were included in our qualitative systematic review. A PRISMA diagram detailing our search results is shown in figure 1. Six two-armed studies compared the performance of SR and ASP techniques.16–21 Four three-armed studies compared the performance of SR+ASP to ASP and SR.22–25 Three two-armed studies compared the safety and efficacy of SR+ASP with SR or ASP alone.26–28

Figure 1

PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) flow chart.

Table 1 summarizes results and characteristics of the studies included within the qualitative review. All the included studies, except Muszynski et al, provided raw data for successful recanalization.23 25 All studies provided data for thrombus location. Data regarding IVT utilization in DMVOs were available in 10 studies.16 17 19 20 22 24–28 Even though Bernsen et al provided overall IVT utilization data, they did not provide separate baseline characteristics for DMVOs.18 Functional independence data were available in nine studies,16–19 21 24–26 28 and eight articles presented complete recanalization16 18 20–22 24 26 27 data. Also, nine studies provided sICH data,16–22 27 28 and seven articles presented SAH data.16 19 21 24 26–28 Alawieh et al provided raw overall functional independence, successful recanalization, and sICH data for their cohort.25 However, they did not share their raw outcome data specifically for three frontline thrombectomy techniques. Instead, they dichotomized their data to ASP alone and SR-based techniques (SR and SR+ASP) and provided raw data for these groups in a matched cohort analysis.

Table 1

Characteristics of the studies included within the qualitative synthesis

Risk of bias

Full details of the risk of bias assessment are available in online supplemental file 1. Of the studies included for qualitative synthesis, two were considered to be low risk of bias, four were moderate risk of bias, four were serious risk of bias, and three were critical risk of bias (figure 2A). The highest quality studies were multicenter prospective studies performed by Gory et al (sub-analysis of the ASTER randomized trial: NCT02523261) and Muszynski et al (ETIS registry: NCT03776877), which provide more robust comparisons of clinical outcomes between the main interventions of interest.16 23 Of note, the retrospective studies performed by Baig et al 22 and Mokin et al 21 were primarily considered to be at a critical risk of bias because their study designs do not have a key focus on comparative analyses of the interventions summarized in this review. As such, these studies should not be used to make inferences about the relative effect of each intervention on patient outcomes. Additionally, a retrospective study by Kim et al 19 was considered to be at a critical risk of bias primarily due to concerns about confounding and improper statistical comparisons of the interventions compared. Overall, the three main sources of bias among studies were bias due to confounding, deviations from intended interventions, and missing data (figure 2B).

Supplemental material

Figure 2

Risk of bias assessment.

Baseline characteristics

Table 2 summarizes baseline patient characteristics. A total of 2422 MT procedures were included in our review, of which we had data for 1964. Separate data for the first-line thrombectomy method were available in 1719 procedures. Of these, 520 were from the ASP group, 844 were from the SR group, and 355 were from the SR+ASP group; the initial thrombectomy technique was not specified in 245 treatments. The most common occlusion site was M2 (1565 procedures, 83.8%). The rate of M2 occlusion was 84.2% (438/520) for the ASP group, 85.9% (725/844) for the SR group, and 85.1% (302/35) for SR+ASP group. The second most common occlusion sites were M3-4 for the SR+ASP group (6.9% 24/355) and were the PCA for the SR and ASP groups (12.7% (107/844) and 9.6% (50/520), respectively). Overall IVT utilization rate was 46.6% (636/1366).

Table 2

Baseline patient characteristics

Outcomes

Table 3 provides detailed information on the performance of first-line thrombectomy techniques. The overall successful recanalization rate was 77.0% (1513/1964) for DMVOs. SR had a successful recanalization rate of 75.6% (638/844), SR+ASP had an 83.7% rate (297/355), while ASP alone had a 74.2% rate (386/520). The overall functional independence rate was 51.3% (851/1659) among DMVOs. The ASP alone group had a functional independence rate of 46.9% (219/467), and the functional independence rates of SR and SR+ASP groups were 51.5% (372/723) and 61.7% (174/282), respectively. The rates of sICH were 8.5% (32/378) for the ASP group, 4.7% (33/700) for the SR group, and 1.1% (1/87) for the SR+ASP group. The SAH rates were 1.8% (4/217) for ASP, 9.3% (26/281) for SR, 11.9% (41/344) for SR+ASP, and 8.3% (85/1023) overall. The overall mortality rate was 19.1% (238/1246), and it ranged between 17.4% and 21.1% across groups (table 3).

Table 3

Safety and efficacy outcomes of first-line thrombectomy techniques.

Contact aspiration versus stent retriever

In a subgroup analysis of the ASTER trial, Gory et al compared the performance of ASP and SR techniques in 79 M2 occlusions.16 There were 48 patients in the ASP group and 31 cases in the SR group. No significant differences were found between the ASP and SR groups in functional independence (54.4% vs 50%, p=0.84), successful recanalization (mTICI ≥2b) (89.6% vs 83.9%, p=0.36), and sICH (6.3% vs 3.2%, p value not reported). Even though the ASP group had a notably higher 90-day mortality rate than the SR group, the difference was not statistically significant (19.6% vs 3.3%, p=0.078).

Atchaneeyasakul et al examined the performance of the ASP and SR techniques in 197 M2 occlusions (77 ASP and 120 SR cases).17 In their retrospective multicenter study, SR thrombectomy provided consistently better safety and efficacy outcomes. The successful recanalization rate (mTICI ≥2b) of the SR group was significantly higher than the ASP group (90% vs 77.3%, p=0.016). Also, sICH and 90-day mortality rates were significantly lower with SR thrombectomy compared with ASP (3.4% vs 16.7%, p=0.001; 9.3% vs 21.1%, p=0.025, respectively). However, the difference in functional independence was not statistically significant (52.1% vs 36.7%, p=0.06).

In a subgroup analysis of the retrospective TOPMOST study, Meyer et al compared the outcomes of ASP and SR techniques in 141 posterior circulation MeVOs (119 PCA P2 occlusions, 22 PCA P3 occlusions).20 Of these 141 cases, 41 were treated with ASP thrombectomy and 100 were treated with SR thrombectomy. There were no significant differences in mRS 0–1 rates (60.5% vs 68.6%, p=0.4), successful recanalization (mTICI ≥2b) (90.2% vs 87%, p=0.596), and 90-day mortality (13.2% vs 10.4%, p=0.750). The sICH rates of the ASP and SR techniques were 2.4% and 3%, respectively (p value not reported).

Kim et al compared the safety and efficacy of the ASP and SR techniques in 41 M2 occlusions (25 ASP and 16 SR cases).19 Their study had a retrospective single center design. The rates of successful recanalization (TICI ≥2b) were 72% in the ASP group, and 87.5% in the SR group. However, the difference was not statistically significant (p=0.441). The sICH occurred only in one case after treatment, which was treated with first-line ASP. Even though safety and efficacy differences were not statistically significant between the ASP and SR groups, SR thrombectomy provided significantly shorter puncture to recanalization times than the ASP group (38.5 min (IQR 31.5–57.25) vs 53 min (IQR 41–74), p=0.045)

In a subgroup analysis of the prospective MR CLEAN registry, Bernsen et al compared the performance of the ASP and SR techniques for different occlusion sites.18 Their study cohort consisted of 2282 patients; however, only 471 were M2 occlusions. Of these 471 cases, 144 were treated with first-line ASP, and 327 were treated with first-line SR thrombectomy. In their study, successful recanalization rates and first-pass efficacy (eTICI ≥2b) of ASP thrombectomy were significantly higher than the SR thrombectomy (72% vs 61%, p=0.04; 53% vs 46%, p=0.03, respectively). However, the differences in sICH and 90-day mortality were not statistically significant (9% vs 6%, p=0.3; 29% vs 22%, p=0.06, respectively).

Contact aspiration versus stent retriever versus combination therapy

In a subgroup analysis of the prospective ETIS registry, Muszinsky et al compared the performance of the ASP, SR, and SR+ASP techniques in 458 M2 occlusions (213 ASP, 49 SR, and 194 SR+ASP cases).23 The differences in successful recanalization (one point or more improvement of the mTICI scale) and functional independence were not statistically significant across groups. However, the use of the SR and SR+ASP techniques were associated with significantly higher procedural complication risk than the ASP alone (ASP vs SR: OR 0.39, 95% CI 0.15 to 0.98, p=0.047; SR+ASP vs ASP alone: OR 1.98, 95% CI 1.02 to 3.83, p=0.043).

Renieri et al conducted a retrospective multicenter study to compare the safety and efficacy of first-line MT strategies in M2 occlusions. There were 465 patients in their study (93 ASP, 133 SR, and 239 SR+ASP cases).24 SR and SR+ASP techniques provided significantly higher rates of successful recanalization (mTICI ≥2b) compared with ASP alone (OR 9.2, 95% CI 1.9 to 44.6; OR 2.6, 95% CI 1.1 to 6.9, respectively). However, on the other hand, intraprocedural SAH rates were also significantly higher with SR and SR+ASP compared with ASP (OR 5, 95% CI 1.1 to 24.3; OR 4.6, 95% CI 1.1 to 20.9, respectively).

Baig et al examined the efficacy of MT in isolated posterior cerebral artery occlusions.22 Their single-center retrospective study consisted of 21 patients, of whom seven were treated with SR+ASP, five were treated with SR alone, and nine were treated with ASP. The successful recanalization rates (mTICI ≥2b) for the first-line treatment techniques were 77% (7/9) for ASP, 80% (4/5) for SR, and 85.7% (6/7) for SR+ASP. The sICH occurred only in one case (1/21), which was treated with first-line aspiration. The overall functional independence rate was 71.4% (15/21) in their study. However, they did not provide separate functional outcomes for first-line treatment methods.

Mokin et al examined the efficacy of MT in 117 M2 occlusions. In their multicenter retrospective study, first-line treatments were ASP in 51 cases and SR in 62 patients.21 Successful recanalization rates (TICI ≥2b) of ASP and SR techniques were 84% and 87%, respectively. Functional independence (53% ASP vs 60% SR) and 90-day mortality rates (16% ASP vs 21% SR) were also similar. However, no p values were reported for the direct comparisons of the ASP and SR techniques.

In their retrospective multicenter experience, Miura et al compared the performance of SR+ASP with the single device approach (ASP or SR).27 Of 65 patients, 28 were treated with SR+ASP and 37 were treated with ASP or SR alone. Both first-pass efficacy (FPE) (mTICI ≥2b) and complete recanalization (mTICI 3) were significantly higher with SR+ASP compared with the single device approach (92% vs 54%, p=0.0008; 75% vs 43%, p=0.012, respectively). However, the differences in successful recanalization (mTICI ≥2b) (100% vs 86%, p=0.064), mortality at discharge (0% vs 1%, p≥0.99), and sICH (0% vs 5%, p=0.501) were not statistically significant.

In their international multicenter study, the STAR investigators examined the performance of frontline thrombectomy techniques in 213 distal vessel occlusions.25 They used regression analyses to investigate the predictors of successful recanalization (mTICI ≥2b) and functional independence. However, frontline thrombectomy techniques were not an independent predictor for these outcomes in their study (SR vs ASP: OR 1.275 (95% CI 0.38 to 4.31), and SR+ASP vs ASP: OR 0.467 (95% CI 0.21 to 1.04) for successful recanalization; and SR vs ASP: OR 0.549 (95% CI 0.2 to 1.54) and SR+ASP vs ASP: OR 1.388 (95% CI 0.58 to 3.33) for functional independence). Additionally, they dichotomized their data for ASP alone and SR-based techniques (SR and SR+ASP) and compared the outcomes of these two groups in a matched cohort of distal vessel occlusion patients. However, the differences in functional independence (47% vs 47%, p>0.05), successful recanalization (75% vs 72%, p>0.05), and intracranial hemorrhage (sICH and parenchymal hematoma, 3% vs 9%, p>0.05) were not statistically significant.

Standard techniques versus blind exchange/mini-pinning (BEMP)

Haussen et al compared the performance of blind exchange/mini-pinning (BEMP) and SR or ASP alone in 169 MeVO thrombectomies.26 In their multicenter retrospective study, BEMP provided significantly or near significantly higher rates of first-pass efficacy, for both successful (FPE mTICI ≥2b) and complete recanalization (FPE mTICI 3), compared with SR or ASP alone (80% vs 56%, p=0.03; 60% vs 40%, p=0.07). However, the differences in overall successful recanalization (84% vs 79%, p=0.58), mortality (21% vs 21%, p>0.99), and SAH (12% vs 6%, p=0.30) were not statistically significant.

Perez-Garcia et al investigated the outcomes of BEMP and SR alone in 106 MeVO treatments (50 SR and 56 BEMP cases).28 In their multicenter retrospective study, the BEMP technique provided significantly higher rates of near-complete/complete recanalization (eTICI >2c) than the SR alone (66.1% vs 46%, p=0.037). Also, sICH rates of the BEMP group were significantly lower than the SR cohort (1.9% vs 12.8%, p=0.038). However, the differences in 90-day mortality and functional independence were not statistically significant (20.8% vs 22.4%, p=0.835; 50.9% vs 53.1% p=0.831, respectively).

Discussion

Our systematic review demonstrated a number of important findings. First, the safety and efficacy outcomes of distal and medium vessel thrombectomy were promising and comparable to other comprehensive studies involving PLVOs.29 Second, the SR+ASP group had high rates of successful recanalization and functional independence rates, while the ASP or SR alone groups had successful recanalization in just over 70% of patients and functional independence in approximately 50%. Third, the ASP alone group had high rates of sICH but low rates of SAH, which is a more direct measure of device-related vessel injury compared with sICH at 24 hours. The descriptive statistics from our systematic review suggest that ASP or SR alone may lag behind the combined treatment technique in recanalization and functional outcomes. Further comparative studies are necessary to determine whether a significant difference exists between ASP, SR, and SR+ASP techniques with respect to angiographic and clinical outcomes.

Three RCTs have compared the performance of stent retriever- and aspiration-based thrombectomy techniques, namely, ASTER (ASP vs SR), COMPASS (ASP vs SR), and ASTER2 (SR vs SR+ASP).11 12 30 ASTER and COMPASS did not show a significant difference in successful recanalization and functional independence between ASP and SR techniques for PLVOs.11 12 However, SR+ASP provided significantly higher rates of successful recanalization than SR alone in ASTER2.30 Nevertheless, COMPASS excluded all DMVOs, and ASTER and ASTER2 enrolled only a limited number of M2 occlusions. In the post-hoc analysis of ASTER, Gory et al showed that SR and ASP techniques are equally effective and safe for M2 occlusions.16 However, the average diameter of proximal M2 is 2.4 mm, and for this reason, its occlusions might be treated with traditional devices.10 Therefore, it would not be prudent to generalize the results of M2 occlusion to all distal occlusions. The STAR investigators recently compared the performance of frontline thrombectomy techniques for only distal vessel occlusions. However, similar to ASTER’s post-hoc study, the differences in successful recanalization and functional independence were not statistically significant.25

In order to provide more comprehensive results, we included all DMVO sites in our review. However, even with our broad inclusion criteria, our study cohort preponderantly consisted of M2 occlusions. Additionally, despite the relatively proximal occlusion site and possibly larger vessel size of the M2 occlusions, we still found relatively low rates of successful recanalization and functional independence for ASP and SR alone (table 3). On the other hand, SR+ASP technique’s successful recanalization and functional independence rates were 83.7% and 61.7%, respectively, which were similar to those of ASTER2.30 Even though SR+ASP technique’s efficacy outcomes were promising for DMVOs, SR and ASP devices failed to provide high successful recanalization rates separately. Currently, only a few low-profile stent retrievers are available on the market, and furthermore, the number of ASP devices that were solely designed for DMVOs is even more limited. Therefore, we believe these low successful recanalization rates of SR and ASP alone groups might be due to the utilization of thrombectomy devices that were primarily designed for PLVOs.

Given the smaller size and thinner wall of the distal and medium vessels, DMVOs are more prone to hemorrhagic complications and thrombectomy-related vessel injury.8 31 The stent retriever exerts a continuous radial force to vessel wall, and furthermore, its metallic struts can damage endothelium during stent retrieval.32–34 Therefore, SR-based techniques have been associated with an increased risk of hemorrhagic complications. Surprisingly, in our study, the ASP group had a high rate of sICH. However, unsuccessful or incomplete recanalization is also one of the most important predictors of sICH.35 36 Therefore, this finding might be due to the low successful and complete recanalization rates of the ASP group. On the other hand, post-thrombectomy SAH is generally iatrogenic and occurs more frequently in DMVOs.8 31 In our study, the ASP group had an SAH rate of 1.8%, and the overall SAH rate was 8.3%. Even though the low SAH rate of the ASP group is promising, further comparative studies are needed to establish the safety profile of ASP thrombectomy in DMVOs.

Our study had several limitations. First, most of the included studies had a retrospective design. Second, our study cohort preponderantly consisted of M2 occlusions. This might have resulted in overestimated safety and efficacy outcomes for DMVOs. Third, sICH definitions were heterogeneous or not described in some of the included papers. Fourth, a few included studies only provided intraprocedural SAH rates. Given the fact that device-related microperforations may not be evident during the procedure, this may have underestimated the overall SAH rate for DMVOs. Fifth, the clinical significance of SAH (symptomatic or asymptomatic) was not reported in most of the included studies. The symptomatic SAH rate would be a more useful metric in device comparison as compared with the overall SAH rate. Finally, in some of the included articles, thrombectomy device size and model were not specified, or treatment outcomes were not specifically reported for device models. Therefore, we were not able to assess the performance of specific thrombectomy devices.

Conclusion

Distal DMVOs are the promising next frontier for the endovascular treatment of acute ischemic stroke. The US Food and Drug Administration has recently approved the protocol of the DISTALS trial, which will investigate the potential benefit of stent retriever thrombectomy over medical treatment without thrombolysis for distal vessel occlusions.37 Even though this trial will be helpful in determining patients who will benefit from MT, the selection of the first-line thrombectomy technique for DMVOs will continue to be a matter of debate. In our systematic review, the SR+ASP technique consistently provided high rates of recanalization and functional independence. Even though the low SAH rate of the ASP group was promising, SR and ASP devices could not provide high recanalization rates separately. Therefore, our findings suggest that current thrombectomy devices are open to improvement in the context of DMVOs.

Data availability statement

Data are available upon reasonable request. The data supporting the findings of this study are available upon reasonable request.

Ethics statements

Patient consent for publication

Ethics approval

Not applicable.

References

Supplementary materials

  • Supplementary Data

    This web only file has been produced by the BMJ Publishing Group from an electronic file supplied by the author(s) and has not been edited for content.

Footnotes

  • CB and NH contributed equally.

  • Contributors All authors contributed to the manuscript. CB, NH, JMP, KMK, DFK and WB were responsible for the conception and design of the work. KH, NH, CB, JMP, AM, PO and HK were responsible for data extraction, literature search, and risk of bias assessment. All authors were involved in the drafting of the article, critical revision of the article, and final approval of the version to be published. CB and NH were equally contributing authors. CB is responsible for the overall content as guarantor.

  • Funding This study was funded by MIVI Neuroscience.

  • Competing interests NH works for and holds equity in Nested Knowledge; KH works for Nested Knowledge and Superior Medical Experts; JMP is employed by and has ownership interest in Superior Medical Experts and Nested Knowledge; AM works for Superior Medical Experts; KMK works for and holds equity in Nested Knowledge and holds equity in Superior Medical Experts; DF consults for Medtronic, Cerenovus, Microvention, Stryker, Balt, RAPID.AI, RAPID Medical, Qapel Medical, Arsenal Medical, Phenox Medical, Perfuze, hold equity in MENTICE, Neurogami, Marblehead, Scientia Medical, NVMed, received research support from Microvention, Penumbra, Stryker, Balt, and Siemens; DFK consults for Medtronic, has ownership interest in Superior Medical Experts, Nested Knowledge Marblehead Medical, Conway Medical, Monarch Biosciences, Piraeus Medical, received research support from Cerenovus, Insera Therapeutics, Medtronic, Microvention, Balt, Monarch Biosciences, Brainomix, and MIVI Neuroscience; WB consults for Medtronic, has ownership interest in Superior Medical Experts, and received research support from MIVI Neuroscience.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.