Optimizating Clot Retrieval in Acute Stroke
The Push and Fluff Technique for Closed-Cell Stentrievers
Background and Purpose—We aimed to investigate the safety and efficacy of the Push and Fluff technique (PFT) as compared with the standard unsheathing technique for closed-cell stent retrievers in acute ischemic stroke.
Methods—Acute ischemic stroke thrombectomy database was analyzed (September 2010 to January 2015) with the Trevo Retriever as a primary strategy. The PFT was compared with our internal standard unsheathing technique and with the Trevo Versus Merci Retrievers for Thrombectomy Revascularization of Large Vessel Occlusions in Acute Ischemic Stroke 2 (TREVO2) trial. Additionally, a silicon flow model was used to compare cell size/configuration, wall apposition/device diameter, and degree of foreshortening/device length across the 2 techniques.
Results—One hundred fifty-one out of 662 patients qualified for the study. The PFT (n=71) was associated with higher rates of first-pass reperfusion (54% versus 35%, P=0.03; 54% versus 32.6%, P<0.01), lower number of passes (1.3±0.8 versus 1.8±1.0, P<0.01; 1.7±1.0 versus 2.4±1.6, P<0.01), and higher rates of modified treatment in cerebral ischemia-3 reperfusion (58% versus 40%, P=0.03; 58% versus 14%, P<0.01) as compared with the standard unsheathing technique (n=81) and the TREVO2 Trevo arm (n=88), respectively. No differences in hemorrhagic complications were observed across the groups. The in vitro model indicated that, compared with standard unsheathing technique, PFT resulted in improved wall apposition (device diameter, 75% larger) and cell size (mean area, 51% larger) at the cost of a mild degree of foreshortening (25% length reduction).
Conclusions—The PFT is safe and leads to optimization of wall apposition and cell size/configuration, resulting in higher chances of first-pass reperfusion, lower number of passes, and better rates of complete reperfusion.
The Trevo Retriever (Stryker Neurovascular, Mountain View, CA) is a closed-cell stent-like nitinol retriever thrombectomy device. There are many theoretical benefits of stent retrievers as compared with the older generation coil retriever–type devices, including (1) immediate flow restoration as a result of the circumferential displacement of the thrombus, (2) better retrievibility as a result of the more evenly distributed radial force along the whole thrombus length, and (3) better clot retention as a result of the ability of the device to expand in diameter during its removal into the larger more proximal vessels.1,2 This type of device has been demonstrated to be superior to previous technology and to significantly benefit patients with large vessel occlusion because of high (yet variable) reperfusion rates.1,3–6
The standard technique for device deployment is, once the device is placed across the occluded segment, to unsheath the device by pulling the microcatheter, leading to a passive stent opening. The radial force of the stent retriever compresses the clot against the blood vessel wall with subsequent incorporation of the clot material through the stent struts.1 Because of its closed cell design, the Trevo Retriever allows a particular deployment maneuver, the Push and Fluff technique (PFT). Theoretically, the PFT may lead to better device opening with optimized wall apposition and larger stent pore area that may allow for incorporation of higher volumes of organized thrombus. We aimed to evaluate the safety and efficacy of the PFT as compared with the standard unsheathing technique (SUT).
This was a review of the interventional database of a tertiary-care academic institution for all cases of endovascular treatment of acute ischemic stroke between September 2010 and January 2015 treated with the Trevo Retriever as the primary thrombectomy device. This study was approved by the local Institutional Review Boards.
A detailed description of the Trevo device is available elsewhere.2 Essentially, the device consists of a 180-cm proximal, 0.018-inch core wire with a 75 cm tapered transition and a closed-cell stent-like-shaped section at the distal end. The overall length of the device is 41 mm (32 mm for the XP—tipless version), with an active clot capture length of 20 mm and with a diameter of 4 mm. Since the implementation of its ProVue version (November 2012), the device has become fully radiopaque.
The SUT for the deployment of the Trevo Retriever constitutes in positioning the device across the occluded segment and unsheathing the device by retracting the delivery microcatheter while immobilizing the microwire (Movie I in the online-only Data Supplement). The PFT consists in positioning the stent retriever across the clot and unsheathing the distal end of the device until good wall apposition (anchoring) is achieved (brief unsheathing step). After this, forward force is applied into the device delivery wire, which generates spontaneous retraction of the microcatheter (pushing step). At the main targeted area (where clot is located), forward tension is applied to the microcatheter while the delivery wire continues to be pushed to maximize the device expansion (fluffing step; Movie II in the online-only Data Supplement). The radiopaque properties of the device allow real-time feedback of the amount of fluffing and wall apposition. In curves, the forward tension of the microcatheter may have to be progressively decreased if the device is seen to collapse/loose apposition to the inner wall. Proper planning for the distal landing zone is needed considering the expected foreshortening of the device that typically happens with the PFT.
In Vitro Model
A silicon flow model (United Biologics, Inc, Tustin, CA) was connected to a flow pump and used under direct fluoroscopic visualization. The model represented the internal carotid–middle cerebral artery junction, with an inner diameter of 3.5 mm and the curved segment and a radius of curvature of 7 mm (to the center of the lumen). It was used to analyze cell size/configuration, wall apposition/device diameter, and degree of foreshortening/device length in a controlled manner. The SUT and the PFT were performed (Movies I and II, respectively, in the online-only Data Supplement). The cell size area was determined using Image J 1.48v software (National Institutes of Health, Bethesda, MA). The area for each cell was calculated through an in vitro still shot angiogram for the SUT and PFT. The most distal cell and the more proximal cell (nonfunctional stent retriever segments) were not included in the analyses. The cell size areas were summed and divided by the total number of cells, leading to the mean cell size for each technique.
Patient Group Comparisons
Our institutional data were dichotomized into patients in whom the PFT versus SUT was used. Our PFT data were then compared with (1) our internal SUT data and (2) the Trevo Versus Merci Retrievers for Thrombectomy Revascularization of Large Vessel Occlusions in Acute Ischemic Stroke 2 (TREVO2) trial Trevo arm patients. Baseline variables, including demographics, clinical, radiological, and procedural characteristics, were analyzed. Baseline noncontrast computed tomography was used to grade the Alberta Stroke Program Early CT Score (ASPECTS). Hemorrhagic complications were categorized as per European Cooperative Acute Stroke Study criteria.7 Reperfusion was assessed by 2 interventionalists, and discrepancies solved by consensus read using the modified treatment in cerebral ischemia (mTICI).8 First-pass reperfusion was defined as the success in achieving mTICI 2b-3 with a single pass of Trevo. Rescue therapy is defined by the need of adjuvant therapy in case revascularization is not achieved with the Trevo device.1 The number of passes was counted only if revascularization is achieved with the Trevo; if a rescue device is used, the number of passes is disregarded, and the patient is categorized as having undergone rescue therapy. For the comparison between PFT versus TREVO2, the total number of passes (with or without the use of rescue therapy) was used. The use of balloon guide catheters or distal access catheters with local aspiration were combined and categorized as using flow control strategy. The efficacy end points included the rates of (1) first-pass reperfusion, (2) number of passes, and (3) mTICI-3. The safety end points included the rates of (1) parenchymal hematoma 1, (2) parenchymal hematoma 2, and (3) subarachnoid hemorrhage (SAH).
Continuous variables are reported as mean±SD or median (interquartile range). Categorical variables are reported as proportions. Between groups, comparisons for continuous/ordinal variables were made with Student t test, Mann–Whitney U test, or ANOVA as appropriate. Categorical variables were compared by chi-square or Fisher exact test as appropriate. Significance was set at P<0.05. Multivariate logistic regression analysis for predictors of good outcome was performed for variables at the 0.1 level of significance on univariate analysis, using a variable selection method. Statistical analyses were performed using IBM SPSS Statistics 21 (IBM-Armonk, NY).
For the comparisons between PFT versus TREVO2 trial, dichotomous outcomes were analyzed by using the number of events in each group and the total number of participants to calculate the risk ratio. For continuous variables, the means and standard deviations from each study were used to calculate the mean difference. A random effects model was used. Analyses were performed with RevMan (version 5.3; Information Management Systems Group, Cochrane Collaboration, and Oxford, United Kingdom).
In Vitro Model
The in vitro experiment demonstrated poor wall device apposition with the SUT (Figure [A]). The maximal device diameter was 1.9 mm, and the device length was 42.8 mm (Figure B). The PFT resulted in better/complete wall apposition, with a maximum device diameter of 3.3 mm (75% larger) and at the cost of a device foreshortening of 8.7 mm (25% device length loss versus SUT). The mean cell size area was 2.4 mm2 for the SUT compared with 3.7 mm2 in the PFT (51% larger; Figure [C and D]).
PFT Versus SUT (Single Center Experience)
From a total of 662 interventions for acute ischemic stroke performed within the study period, 151 patients underwent intra-arterial therapy with Trevo as the primary device for proximal occlusions. Seventy patients (46%) were treated with the PFT versus 81 patients (54%) with SUT. Baseline characteristics were similar among the 2 groups, except for higher frequency of tandem cervical and cerebral occlusions in the PFT group (Table 1). The PFT was associated with a higher rate of first-pass reperfusion (54% versus 36%; P=0.03) and a lower number of passes (1.3±0.8 versus 1.8±1.0; P<0.01), despite similar use of rescue therapy. More patients in the PFT had the use of flow control (83% versus 21%; P<0.01). mTICI-3 reperfusion was achieved more frequently in the PFT group (58% versus 40%; P=0.03), whereas hemorrhagic complications and clinical outcomes were similar. Multivariate analyses indicated that the PFT was independently associated with a lower number of Trevo passes (P=0.01) and higher rates of first-pass reperfusion (P=0.01) and complete (mTICI-3) reperfusion (P<0.01; Table 2).
PFT Versus SUT (TREVO2 Trial Experience)
The comparison between the PFT versus TREVO2 cohorts indicated that the TREVO2 patients were older, were more commonly dyslipidemic, and less commonly had the use of flow control during intervention. On the other hand, the PFT patients less commonly received IV tissue-type plaminogen activator, had longer time from last seen normal to groin puncture, and more frequently had basilar occlusions. The mean number of passes was significantly lower in the PFT group (1.7±1.0 versus 2.4±1.6; P<0.01), and the number of first-pass reperfusion was higher (54% versus 32%; P<0.01). The frequency of mTICI-3 reperfusion was substantially higher in the PFT (58% versus 14%; P<0.001), whereas hemorrhagic complications and clinical outcomes were similar (Table 1).
The PFT for Trevo Retriever deployment was found safe and effective. It was associated with a higher rate of successful reperfusion on first pass, a lower number of stent-retriever passes, and higher rates of complete reperfusion as compared with both our local and the TREVO2 trial SUT cohorts.
With the confirmation that the endovascular treatment for acute ischemic stroke is greatly beneficial for patients with large vessel occlusion, accommodation of further therapy is warranted. The significant variation of reperfusion rates among the different trials evaluating intervention for acute ischemic stroke might reflect, in part, different procedural techniques.4,6 We have demonstrated that the delivery technique of closed-cell stent retrievers impacts procedural outcomes. The potential influence on clinical outcomes remains to be demonstrated.
A previous report has evaluated the impact of the delivery technique in the wall apposition for a closed-cell nitinol self-expanding stent (typically used for stent-assisted coiling). The report indicated that the unsheathing technique tended to cause the stent to follow the contour of the inner curve, with poor apposition on the outer curve, whereas a dynamic microcatheter pullback and microwire push would optimize stent deployment and minimize malapposition.9 The Trevo Retriever has a similar design, and its behavior during delivery should follow similar physical principles. The improved wall apposition was found to result in a lower number of needed passes for reperfusion and better ability to remove the entire clot, leading to complete reperfusion. We postulate that the enhanced performance of the PFT may relate to the increased radial force and wall apposition coupled with an enlarged cell size/optimized cell configuration, facilitating the integration and internalization of the thrombotic material.
The major theoretical concern related to this technique was the potential association with adverse events related to the addition of radial force or forward movement of the device. Subarachnoid hemorrhage is not uncommon and has been reported in 0.9% to 12% of patients in recent trials involving stent retrievers and has been suggested to potentially result from stretching of arterioles and accompanying venules in the subarachnoid peri-Sylvian subarachnoid space.1,6,10 The frequency of hemorrhagic complications, including subarachnoid hemorrhage, was not different among the patients treated with the PFT and the other 2 control groups. This may relate to the fact that the pathogenesis of subarachnoid hemorrhage is typically not from vessel perforation, and because the distribution of pressure between device and arterial wall occurs somewhat homogeneously within the vessel lumen, the force distributes itself along the entire device length.
This study has weaknesses inherent to its retrospective design. The feasibility, safety, and potential benefit of this technique with other stent retrievers remains to be investigated. The Solitaire (Medtronic, MN) stent retriever has been the most commonly used device in the recent thrombectomy trials; however, it has a parametric design (eg, folded architecture with overlapping struts) and is not radiopaque. Therefore, in our assessment, the Solitaire may not be as suitable to the PFT, and we have limited our use and evaluation of the PFT to the Trevo device given its closed cell design. The device foreshortening constitutes a potential problem with the PFT; however, the stent retriever typically lands accurately with appropriate technique and planning. Moreover, the availability of longer stent retrievers would easily address this issue. The use of flow control has been associated with better reperfusion rates and outcomes.11 Because the more common use of flow control could theoretically be responsible for the beneficial effects of this technique, we performed multivariate analyses that revealed that the total number of passes remained independently lower, and the rates of first-pass reperfusion and complete reperfusion remained independently higher with the PFT after adjustments for multiple variables, including flow control. We cannot completely refute the possibility that some operators may have used a similar technique in the TREVO2 trial; however, according to both the study sponsor and the neurointerventional Principal Investigator, the investigators were oriented to use the SUT throughout the whole trial, and to their knowledge, there was no use of any other deployment techniques. Furthermore, we think that the ability of optimally performing the PFT only became possible after the introduction of the radiopaque Trevo ProVue in the market, which happened after the closure of the TREVO2 trial. The flow model does not accurately replicate the frictional coefficient or the stiffness of a native vessel wall.9 Otherwise, the strengths include a comparison of homogeneous local groups and the fact that the findings were reinforced when matched to the TREVO2 trial data.
The PFT is safe and leads to optimization of wall apposition and cell size/configuration, resulting in higher chances of first-pass reperfusion, lower number of passes, and better rates of complete reperfusion compared with the SUT. The feasibility of the use of this technique with other stent retrievers remains to be investigated.
Dr Nogueira has the following disclosures: Stryker Neurovacular (Trevo Versus Merci Retrievers for Thrombectomy Revascularization of Large Vessel Occlusions in Acute Ischemic Stroke 2 [TREVO2] Trial Principal Investigator [PI], DWI or CTP Assessment With Clinical Mismatch in the Triage of Wake Up and Late Presenting Strokes Undergoing Neurointervention [DAWN] Trial PI), Covidien (Solitaire With the Intention For Thrombectomy [SWIFT] and SWIFT as Primary Endovascular Treatment [SWIFT-PRIME] Steering Committee, Solitaire Flow Restoration Thrombectomy for Acute Revascularization [STAR] Trial Core Laboratory), and Penumbra (3-D Separator Trial Executive Committee). The other authors report no conflicts.
The online-only Data Supplement is available with this article at http://stroke.ahajournals.org/lookup/suppl/doi:10.1161/STROKEAHA.115.010044/-/DC1.
- Received May 11, 2015.
- Revision received July 21, 2015.
- Accepted July 30, 2015.
- © 2015 American Heart Association, Inc.
- Nogueira RG,
- Lutsep HL,
- Gupta R,
- Jovin TG,
- Albers GW,
- Walker GA,
- et al
- Nogueira RG,
- Levy EI,
- Gounis M,
- Siddiqui AH
- Saver JL,
- Jahan R,
- Levy EI,
- Jovin TG,
- Baxter B,
- Nogueira RG,
- et al
- Berger C,
- Fiorelli M,
- Steiner T,
- Schäbitz WR,
- Bozzao L,
- Bluhmki E,
- et al
- Zaidat OO,
- Yoo AJ,
- Khatri P,
- Tomsick TA,
- von Kummer R,
- Saver JL,
- et al
- Heller RS,
- Malek AM
- Yoon W,
- Jung MY,
- Jung SH,
- Park MS,
- Kim JT,
- Kang HK
- Nguyen TN,
- Malisch T,
- Castonguay AC,
- Gupta R,
- Sun CH,
- Martin CO,
- et al