Background The optimal interaction between stent struts and thrombus is crucial for successful revascularization in endovascular stroke therapy with stent retrievers. Deploying the stent retriever by actively pushing it into the thrombus increases the radial force with which the stent struts expand into the thrombus.
Objective To examine the active push deployment (APD) technique in an in vitro model and present our clinical experience with this technique.
Methods In an in vitro experiment we investigated the configuration of a Solitaire and a Trevo ProVue device (both 4×20 mm), depending on whether the devices were deployed using the APD technique or simple unsheathing. We retrospectively assessed the effectiveness and safety of this technique by analyzing 130 patients with large vessel occlusions (carotid T or M1 segment of the middle cerebral artery), who received endovascular treatment with a Trevo device (4×20 mm) that was deployed using the APD technique.
Results In vitro experiment: the APD technique improved apposition of the devices to the vessel wall. There was widening of 30% (Trevo) and 19% (Solitaire) at the cost of a shortening of 5% and 4%, respectively, when the devices were deployed in a carotid T model. Clinical study: the revascularization rate (Thrombolysis in Cerebral Infarction ≥2b) with the Trevo device was 90%. There were no retriever-associated dissections or perforations in 278 retrieval maneuvers.
Conclusions The APD technique improves apposition of the tested devices to the vessel wall. The widening effect comes at the cost of minimal shortening of the devices. Our clinical experience shows that using the APD technique to deploy the Trevo device is effective and safe.
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The development of modern stent retrievers was a milestone in endovascular stroke treatment. Today, various stent retrievers are available but the basic principle of thrombus removal is the same. Stent retrievers are usually deployed by pulling back the microcatheter in which the stent retriever is positioned (figure 1). When the stent retriever expands passively into its original shape, the struts of the stent retriever work into the thrombus and interact with it. The optimal interaction between the stent struts and the thrombus is a crucial factor for successful revascularization.1 ,2 A common technique for increasing the radial force with which the stent struts work into the thrombus is to unsheathe the stent retriever by actively fluffing and thereby pushing it into the thrombus (figure 1).3 Haussen et al recently published a series,3 reporting their experience with this technique using a Trevo ProVue device (Stryker, Kalamazoo, California, USA). The authors hypothesized that actively fluffing stent retrievers works only with tube-shaped stent retrievers and that fluffing the Solitaire stent retriever (ev3, Irvine, USA), which has an open-ring-shaped profile, might not be possible. In this paper we present results from an in vitro study, in which we examined the active push deployment (APD) technique with a Solitaire device and a Trevo ProVue device. We also describe our clinical experience with the APD technique and report the effectiveness and safety of this method using a Trevo stent retriever, which is the stent retriever that has been predominantly used in our institution since 2011.
In vitro model
A detailed description of the APD technique is given in figure 1. We investigated the configuration of Solitaire and Trevo ProVue devices (both 4×20 mm) depending on whether the devices were deployed using the APD technique or simple unsheathing. We used three vascular silicone models: (1) a nearly straight tube with an inner diameter of 3 mm; (2) a curved tube with an inner diameter of 3 mm, a curve angle of 60°, and a curve diameter of 9 cm; (3) a slightly curved cone-shaped tube with a proximal and distal diameter of 5 mm and 3 mm, respectively (figure 1). These models correspond approximately to the M1 segment of the middle cerebral artery (model 1) and the carotid T (model 3). Both devices were deployed using both techniques in all three models. All maneuvers were repeated five times by the same investigator, resulting in a total of 60 deployments. A neuroradiologist, who was blinded to the deployment technique, assessed the length as well as the proximal and distal diameter of the devices in random order. The length of a device was defined as the distance between the proximal and distal radiopaque markers. The model was perfused with a mixture of physiological saline solution and iodinated contrast agent (iopamidol, 300 mg/mL; Bracco Imaging GmbH, Germany) in a dilution of 20:1 and at a temperature of 22°C. All procedures were performed on a biplane Siemens angiography system (Artis Zee, Siemens, Forchheim, Germany).
In our prospectively maintained stroke registry we identified 326 patients, who had received endovascular treatment for stroke caused by large vessel occlusions in the anterior circulation in our institution between February 2010 and March 2015. One hundred and fifty-five patients met the inclusion criteria of occlusion of the carotid T, or the M1 segment of the middle cerebral artery (MCA; with and without involvement of M2 branches) and endovascular treatment with a Trevo stent retriever (4×20 mm). The APD technique, which was adopted as our standard deployment technique shortly after the introduction of the Trevo Pro 4 stent retriever, was used in 130 patients. These patients were included in our retrospective analysis.
Radiological and procedural data for this study comprised the site of the large vessel occlusion, type of IA treatment (including bridging therapy) and devices, number of stent retriever passes, result of recanalization (Thrombolysis in Cerebral Infarction (TICI)), and peri- and post-treatment complications. Hemorrhagic events were defined according to the European Cooperative Acute Stroke Study (ECASS) classification.4 Radiological data were assessed by the treating neuroradiologist and re-evaluated for this study by a second neuroradiologist who was blinded to all clinical data. If there was disagreement between the observers, a reference standard was established for statistical analyses in a consensus reading.
Data are expressed as mean±SD unless indicated otherwise. Student's t test was used for comparing stent retriever length and diameter after testing our data for normal distribution with a Shapiro–Wilk test. p Values ≤0.05 were defined as significant. All statistical analyses were performed with SPSS V.23 software (IBM, Armonk, New York, USA).
In vitro model
Stent retriever delivery with the APD technique resulted in significant shortening of both devices (table 1 and figure 1). These changes were significant on a submillimeter scale when the vessel diameter was smaller than the device diameter (models 1 and 2) (table 1). When the vessel diameter was greater than the device diameter (model 3), pushing resulted in significant widening and shortening of the devices on a millimeter scale with an improved apposition of the devices to the vessel wall (table 1 and figure 1).
Seventy-six of 130 (58%) patients were female. Mean age was 72.5±15.1 years (median 75.7; range 19.5–105.0 years). Ninety-four (72%) patients received systemic bridging thrombolysis. Sixteen (12%) patients received intra-arterial thrombolysis after mechanical thrombectomy. Fourteen of the latter also received systemic thrombolysis.
The occlusion site was the carotid T in 26 (20%) cases and the M1 segment of the MCA in 104 cases (80%). Fifteen of the latter also had occlusion of M2 branches. Complete or near complete revascularization (TICI≥2b) was achieved in 115/130 (88%) cases. Complete revascularization (TICI=3) was achieved in 85/130 (65%) patients. Revascularization was not possible (TICI≤1) in 11 (8%) patients. A Trevo device was the device of first choice in 124/130 (95%) cases and the only device in 101/130 (78%) cases. Revascularization (TICI≥2b) was achieved after a single pass in 45/101 (45%) and overall in 91/101 (90%) of the latter cases. Revascularization according to the TREVO 2 study criteria (TICI≥2a) was achieved in 95/101 (94%) cases.5 A total of 278 passes were performed with a Trevo device. One hundred deployment maneuvers in 52 patients were performed with a Trevo Pro 4 device (with rather radiolucent stent struts), whereas the remaining 178 deployment maneuvers were performed in 78 patients with a radiopaque Trevo ProVue device. On average, 2.1±1.3 passes with a Trevo device were needed for vessel recanalization (median 2; range 1–7). Overall, 2.5±1.7 stent retriever passes were needed for vessel recanalization (median 2; range 1–11). A Solitaire device was used in 15 cases. Other devices were used as follows: Separator 3D (Penumbra, Alameda, USA) (seven cases), MindFrame (MindFrame, Irvine, USA) (five cases), pREset (Phenox, Bochum, Germany) (two cases), and BONnet device (one case) (Phenox, Bochum, Germany). All devices, except for the Trevo devices, were deployed using the standard technique.
Five (4%) cases of vessel perforation by the microwire and/or microcatheter occurred, with subsequent subarachnoid hemorrhage that was accompanied by cerebral hemorrhage (ECASS: PH2) in three cases. No cases of stent retriever deployment- or retrieval- associated dissections or perforations were seen.
Our results support the findings of Haussen et al,3 who have shown that deploying stent retrievers using the APD technique improves the apposition of the stent struts to the vessel wall (table 1 and figure 1). It is noteworthy that the APD technique also worked with a Solitaire device, which has an open-ring architecture with folded overlapping rims (table 1 and figure 1). Even though this architecture would suggest only small changes, we were able to significantly widen the Solitaire stent. This effect is most notable when the proximal vessel diameter is greater than the device diameter, which is the case in occlusions of the carotid T. In our carotid T model (model 3) the APD technique increased the proximal diameter by 30% (Trevo) and 19% (Solitaire) at the cost of a shortening of 5% (Trevo) and 4% (Solitaire). Even though the widening and shortening effects were submillimetric in smaller vessels, our findings also imply that it is possible to apply additional radial force in smaller vessels such as the M1 or M2 segments of the MCA. Thus, it is reasonable to assume that the APD technique has a marked advantage over the standard technique in small vessels when there is thrombus which inhibits opening of the stent retriever.
In daily clinical practice the most important question is whether the APD technique improves revascularization rates without increasing the risk for dissections and perforations due to the additionally applied radial force. Haussen et al3 retrospectively compared 70 cases using the APD technique with 81 cases using the standard technique. The authors report a significantly higher full recanalization rate (TICI=3) of 58% with the APD technique compared with 40% with the standard technique. However, the authors also report an overall non-significant lower rate of near complete recanalization (TICI≥2b) of 81% with the APD technique compared with 87% with the standard technique. A large prospective randomized study is needed to determine whether the APD technique produces a more favorable procedural and clinical outcome. As our data do not allow such a comparison, as our study was restricted to a discussion of the effectiveness and safety of our method. Our revascularization (TICI≥2b) rate of 88% is comparable to results obtained by recent large randomized studies that reported revascularization rates of 56–88% in comparable occlusion sites with various stent retrievers.6–10 For the cases in which the Trevo was the only device used, our revascularization rates of 95% (TICI≥2a) and 90% (TICI≥2b) are comparable to the 91% (TICI≥2b) indicated by Kabbasch et al11 in their analysis of 76 patients, and also comparable to the 88% (TICI≥2a) indicated by Nogueira et al5 in the TREVO 2 study.
As no cases of deployment- or retrieval-associated dissections or perforations occurred in 278 retrieval maneuvers with the Trevo device, our deployment and retrieval technique can also be regarded as safe. Haussen et al3 expressed the concern that low visibility of a given stent retriever (specifically the Solitaire stent retriever) might pose a danger for vessel rupture when deployed with the APD technique. Even though we did not analyze the safety of the APD technique using the Solitaire stent retriever, our data do not seem to support this hypothesis, as there were no deployment-related complications in 100 maneuvers, which were performed with a Trevo Pro 4 stent retriever that is not radiopaque. Nevertheless, for reasons of safety we would also advocate that the APD technique should be used with caution if the stent retriever cannot be visualized.
A limitation of our study is the simple design of our in vitro experiment without artificial clots. Since an experiment that involves all possible combinations of stent retrievers, vessel configurations, thrombus formations, and retrieval techniques is almost impossible, we decided to focus on two common but different stent retrievers in simple but valid settings. Hence, our experiments may serve as a first step for more comprehensive experiments. A further limitation is the retrospective analysis of our clinical data. Even though we could show that the APD technique is effective and safe, our comparison with the literature has to be interpreted with caution, as it is very likely that other neuroradiologists have used the APD technique without reporting it.
The APD technique improves apposition of the Solitaire and the Trevo devices to the vessel wall, particularly when the stent retrievers are deployed in a carotid T model. Our clinical experience shows that the APD technique using the Trevo stent retriever is effective and safe. Future prospective randomized studies may evaluate whether this technique improves recanalization rates and clinical outcome.
Contributors All authors: conception and design; acquisition of data; analysis and interpretation of data; drafting of the article; critically revision of the article.
Competing interests M-AB: non-financial support from Covidien, Stryker, Terumo/Microvention. MW: grants from Stryker Neurovascular, Siemens Healthcare; personal fees from Stryker Neurovascular, Silkroad Medical, Siemens Healthcare, Bracco; non-financial support from Codman Neurovascular, Covidien, Abbott, St Jude Medical, Phenox, Penumbra, Microvention/Terumo, B Braun, Bayer, Acandis, ab medica.
Ethics approval RWTH Aachen University.
Provenance and peer review Not commissioned; externally peer reviewed.