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Abstract
Background Longer stent retrievers have recently become available and have theoretical advantages over their shorter counterparts. We aim to evaluate whether stent retriever length impacts reperfusion rates in stroke thrombectomy.
Methods This was a retrospective analysis of a prospectively collected thrombectomy database in which equal diameter (4 mm) stent retrievers were used as the first-line strategy for intracranial internal carotid or middle cerebral artery M1 or M2 occlusions along with a balloon guide catheter from June 2011 to March 2017. The population was dichotomized into long (Trevo 4×30 mm/Solitaire 4×40 mm) or short (Trevo 4×20 mm/Solitaire 4×20 mm) retrievers. The primary outcome was first-pass modified Thrombolysis in Cerebral Infarction (mTICI) 2b/3 reperfusion.
Results Of 1126 thrombectomies performed within the study period, 420 were included. Age, gender, National Institutes of Health Stroke Scale, ASPECTS, IV tissue plasminogen activator use, stroke etiology, occlusion site, time from last-known-normal to puncture, distribution of Trevo and Solitaire, and the use of newer generation local thromboaspiration devices were comparable between the long and short retrievers. The short retriever group had more frequent hypertension, dyslipidemia, and atrial fibrillation. First-pass mTICI 2b/3 reperfusion was more common in the long retriever group (62% vs 50%; P=0.01). Parenchymal hematomas type 2, subarachnoid hemorrhage, 90-day modified Rankin Scale score 0–2, and mortality were comparable. Multivariable analysis indicated that long retriever (OR 2.2; 95% CI 1.3 to 3.6; P=0.001), radiopaque device (OR 2.1; 95% CI 1.2 to 3.4; P=0.003), and adjuvant local aspiration (OR 2.4; 95% CI 1.3 to 4.3; P=0.003) were independently associated with first-pass reperfusion.
Conclusions The use of longer stent retrievers is an independent predictor of first-pass mTICI 2b/3 reperfusion. First-pass reperfusion was also associated with the use of radiopaque devices and adjuvant local aspiration.
- thrombectomy
- stroke
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Introduction
Stent retrievers have revolutionized mechanical thrombectomy for large vessel occlusion acute ischemic stroke (LVOS).1 Stent retrievers with larger diameters do not appear to provide clear benefits,2 while retrievers with smaller diameters now allow safe thrombectomy in distal arteries.3 Longer stent retrievers have recently become available and have theoretical advantages over their shorter counterparts, including a larger area of device/thrombus interaction and lower chances of missing the target site. We aim to evaluate if the device length impacts reperfusion rates in stroke thrombectomy.
Methods
Patient selection
This was a retrospective analysis of prospectively collected single institutional data. We included all thrombectomies in which equal diameter (4 mm) stent retrievers were used as the first-line strategy for intracranial internal carotid artery (ICA), middle cerebral artery (MCA)-M1 and MCA-M2 occlusions along with a balloon guide catheter (9 Fr Merci Balloon Guide Catheter, Concentric Medical, California, USA) from June 2011 to March 2017. Exclusion criteria were: transferred patients who were taken directly to angiography without repeat imaging; posterior circulation, MCA-M3, anterior cerebral artery occlusions; larger or smaller diameter stent retrievers, dual retriever technique, other devices as first-line strategy. The local Internal Review Board approved the study.
Device characteristics
Solitaire (Medtronic Neurovascular, Minnesota, USA) and Trevo (Stryker Neurovascular, California, USA) are laser-cut, closed-cell, nitinol stent retrievers. Trevo is available in 4×20 mm (32 mm total length; 21 mm non-tapered length for clot capture) and 4×30 mm (44 mm length; 35 mm non-tapered length) configurations (figure 1A). The device is marked with one proximal and three distal radiopaque markers. The Trevo ProVue version includes the integration of platinum wires into the stent struts to optimize fluoroscopic visualization (figure 1B). Solitaire is available in 4×20 mm (31 mm length; 20 mm non-tapered length) and 4×40 mm (50 mm length; 40 mm non-tapered length) configurations (figure 1A). The device is marked with one proximal and three distal radiopaque markers. The Platinum version includes the integration of evenly spaced platinum markers intended to improve device visualization (figure 1B). Solitaire Platinum and Trevo Provue versions were defined as radiopaque devices.
Illustrative image of the different 4 mm stent retriever lengths and fluoroscopic characteristics. (A) Macroscopic and (B) fluoroscopic appearance of the devices. From top to bottom: Solitaire 4×40 mm; Trevo 4×30 mm; Solitaire 4×20 mm; Trevo 4×20 mm.
Statistical analysis
The population was dichotomized into (1) long (Trevo 4×30 mm/Solitaire 4×40 mm) and (2) short (Trevo 4×20 mm/Solitaire 4×20 mm) retrievers and compared. The primary outcome was first-pass reperfusion (modified TICI (mTICI) 2b/3 with the first pass). Continuous variables are reported as mean±SD or median (IQR). Categorical variables are reported as proportions. Between-group comparisons were made with the Student t-test/Mann–Whitney U test or χ2/Fisher exact test. Significance was set at P<0.05. Multivariate logistic regression analyses were performed for variables with <0.1 level of significance on univariate analysis. Analyses were performed using SPSS Statistics 24 (IBM, Armonk, New York, USA).
Results
Of 1126 thrombectomies performed within the study period, 420 were included. A total of 221 patients (53%) were treated with long retrievers and compared with 199 (47%) treated with short devices. Baseline characteristics were comparable, with the exception of more frequent hypertension, dyslipidemia and atrial fibrillation in patients treated with short devices (table 1). The use of adjuvant local aspiration (upfront use of any distal access catheter ≥130 cm along with retrievers) and the percentage of long devices were not different between device types. First-pass reperfusion was more common in the long retriever group (62% vs 50%; P=0.01) as well as final mTICI 2b/3 (98% vs 94%; P=0.01). Radiopaque devices were more common in the long retriever arm. Clinical outcomes were comparable between groups (table 1). Multivariable logistic regression analysis for the primary outcome indicated that long retriever (OR 2.2; 95% CI 1.3 to 3.6; P=0.001), use of radiopaque devices (OR 2.1; 95% CI 1.2 to 3.4; P=0.003), and adjuvant local aspiration (OR 2.4; 95% CI 1.3 to 4.3; P=0.003) were independently associated with first-pass reperfusion (table 2).
Univariate analysis comparing long versus short retrievers
Multivariable regression for first-pass reperfusion
Sensitivity analysis forcing hypertension, hyperlipidemia, and atrial fibrillation into the multivariable model confirmed the aforementioned independent associations after additional adjustments (long stent retriever OR 2.2; 95% CI 1.3 to 3.7). Considering the potential impact of interventionist experience, we added the variable ‘operator’ into the multivariable model and found that it did not have an impact on the rates of first-pass reperfusion (OR 1.09; 95% CI 0.97 to 1.23) while the effect of long stent retriever remained intact (OR 1.8; 95% CI 1.1 to 3.2). In another analysis including patients with basilar artery occlusions and anterior circulation occlusions in which a balloon guide catheter was not used, the effect of a long (n=236) versus short retriever (n=357) led to consistent results (long stent retriever OR 2.3; 95% CI 1.3 to 3.9).
Discussion
We observed higher rates of first-pass reperfusion in the treatment of LVOS with longer stent retrievers. Moreover, first-pass reperfusion was found to be independently associated with the use of adjuvant local aspiration and radiopaque devices.
Currently, refinements in procedural techniques have become an important facet of thrombectomy research. The development of stent retriever deployment techniques, such as active deployment, has been shown to affect procedural outcomes.4 5 Technological advancements have resulted in the release of retrievers with smaller diameters (3 mm), permitting the safe approach to very distal occlusions.3 Considering the potential stent retriever foreshortening on active deployment, longer devices become very attractive.4 The higher chances of first-pass reperfusion with longer devices may have diverse explanations. Longer thrombi would potentially provide a larger surface for device integration and uniform distribution of forces along the clot during traction. Longer devices may allow precise placement by increasing the margin of error in patients with tortuous anatomy or restlessness. A longer device may enhance device purchase distal to the clot, increasing the chances of dragging the clot out if the primary integration to struts fails.
Final reperfusion rates in clinical practice are impacted by the use of a variable number of device passes, the use of adjuvant techniques, or the use of alternative devices. Hence, first-pass reperfusion is a very appealing method to investigate device/technique performance. We showed that the use of adjuvant local aspiration leads to higher rates of first-pass reperfusion when coupled with the use of balloon guide catheter flow arrest. The evidence for local aspiration combined with a stent retriever mostly comes from single-arm studies demonstrating feasibility and safety, and often excluding concomitant use of balloon guide catheters. Studies comparing techniques are limited and our findings corroborate that, despite the additional cost, the use of adjuvant distal access catheters for aspiration leads to improved procedural performance.6–8 We have observed that the use of radiopaque devices was independently associated with the chances of first-pass reperfusion. A previous investigation demonstrated that the improved visualization of radiopaque stent retrievers led to changes in the methodology of the device use, which may explain the improved performance observed in the present cohort.9
This study has limitations inherent to retrospective analyses. The single-center design may limit generalizability but offers the theoretical advantage of a homogenous population/technique. There were higher rates of hypertension, dyslipidemia, and atrial fibrillation in the short stent retriever group. However, there were no differences in the levels of pretreatment systolic blood pressure which, contrary to the diagnosis of hypertension, has been shown to impact reperfusion after endovascular therapy.10 Atrial fibrillation may be associated with lower chances of reperfusion; nevertheless, the aforementioned associations remained significant after adjustments. Longer retrievers could have disadvantages, such as a larger area of interface with the vessel and consequently more friction during retrieval, especially in distal and/or tortuous vessels. In the present study, subarachnoid hemorrhage rates were comparable between groups.
Conclusion
The use of longer stent retrievers was found to independently predict first-pass reperfusion. First-pass reperfusion was also associated with the use of radiopaque devices and adjuvant local aspiration.
Footnotes
Contributors DCH: Study conception, design of the work, acquisition of data, statistical analysis, interpretation of data, drafting of the manuscript. ARA-B: Data acquisition, critical revision of manuscript. JAG: Data acquisition, critical revision of manuscript. MB: Data acquisition, critical revision of manuscript. CB: Data acquisition, critical revision of manuscript. NB: Critical revision of manuscript. MRF: Critical revision of manuscript. RGN: Design of the work, acquisition of data, interpretation of data, critical revision of manuscript. All authors gave final approval of the version to be published, and are in agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests RGN: Stryker-Neurovacular (Trevo-2 and DAWN/Trial PI), Covidien (SWIFT and SWIFT-PRIME/Steering- Committee, STAR Trial/Core-Lab), Penumbra (3-D Separator Trial/Executive-Committee).
Patient consent Not required.
Ethics approval Emory University IRB.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement The unpublished data from this dataset is held by Grady Memorial Hospital/Emory University and DCH/RGN. Requests for data sharing would be required to be discussed with them directly.