Soft Clot Research Articles

Experimental comparison of first-pass effect between direct thromboaspiration and combined thrombectomy in the setting of distal basilar occlusion.

Studies investigating endovascular therapy in vertebro-basilar stroke have led to controversial results in the past, but recent randomized trials seem to show an effectiveness superiority of endovascular therapy versus best medical treatment. However, uncertainty remains concerning many aspects of thrombectomy in acute basilar artery occlusion, notably technical considerations. This study compared the first-pass effect of direct thromboaspiration and combined thrombectomy in the setting of distal basilar occlusion. An in-vitro experimental set-up was used, consisting of a vascular phantom model and thrombus analogs of different consistencies to mimic human clots. Thrombus analogs were injected into the model through the vertebral artery and flowed to the basilar distal third to mimic a distal basilar occlusion. Ten procedures were performed for each thrombus analog stiffness and technique (direct thromboaspiration versus combined thrombectomy). Direct thromboaspiration showed an overall first-pass effect rate of 83.3% (25/30) and was particularly effective for ultra-soft and soft clot analogs, but decreased for hard clot analogs. Combined thrombectomy had an overall first-pass effect rate of 56.7% (17/30). The effect rate for ultra-soft and soft clot analogs was 60% and 50% for hard clot analogs. In the softer clot analogs, the stent-retriever device used for the combined thrombectomies tended to deviate the clot analog from a co-axial trajectory with the aspiration catheter. In the context of distal basilar occlusion, our in-vitro results showed that higher first-pass effect rates were achieved with direct thromboaspiration compared to combined thrombectomy in all types of thrombus analogs.

Can micro-guidewire advancement forces predict clot consistency and location to assist the first-line technique for mechanical thrombectomy?

The identification of specific clot characteristics before mechanical thrombectomy (MTB) might allow the selection of the most effective first-line technique, thus potentially improving the procedural outcome. We aimed to evaluate if the microwire push forces could extrapolate information on clot consistency and extension before MTB, based on clot mechanical properties. We measured in vitro the forces exerted on the proximal extremity of the guidewire during the advancement and retrieval of the guidewire through clot analogs of different compositions. In addition, we analyzed the forces exerted on the guidewire to extrapolate information about the location of the proximal and distal extremities of the clot analogs. The maximum forces recorded during the whole penetration phase were significantly different for hard and soft clots (median values, 55.6 mN vs 15.4 mN, respectively; P<0.0001). The maximum slope of the force curves recorded during the advancement of the guidewire for the first 3 s of penetration also significantly differentiated soft from hard clot analogs (7.6 mN/s vs 23.9 mN/s, respectively; P<0.0001). In addition, the qualitative analysis of the shape of the force curves obtained during the advancement and retrieval of the guidewire showed a good potential for the identification of the proximal and distal edges of the clot analogs. Our results demonstrated that it was possible to differentiate between soft and hard clot analogs. Furthermore, force measurements could give important information about the location of the clot extremities. Such an approach might support the selection of the first-line MTB technique, with the potential to improve the outcome.

Partial (SAVE) versus Complete (Solumbra) Stent Retriever Retraction Technique for Mechanical Thrombectomy: A Randomized In Vitro Study.

Mechanical thrombectomy has become a first-line treatment for acute ischemic stroke. Several techniques combining stent retrievers and distal aspiration catheters have been described. We aimed to characterize the efficacy of 2 commonly used techniques according to clot characteristics. Soft (mean stiffness = 95.77 [SD, 5.80] kPa) or stiff (mean stiffness = 205.63 [SD, 6.70] kPa) clots (3 × 10 mm and 2 × 10 mm, respectively) were embolized to the distal M1 segment of the MCA in an in vitro model. The technique was randomly allocated (1:1): stent retriever assisted vacuum-locked extraction (SAVE) versus complete retraction (Solumbra). The primary end point was the percentage of first-pass recanalization. Secondary end points were periprocedural distal embolization measures. A total of 130 mechanical thrombectomies were performed (50 for soft clots and 15 for stiff clots per arm). Overall, the rate of first-pass recanalizaton was 35% with Solumbra and 15% with SAVE (P < .01). For stiff clots, the first-pass recanalizaton was equal for both methods (27%; P = 1.00). With soft clots, the first-pass recanalizaton was higher with Solumbra (38%) than with SAVE (12%; P < .01). When we used soft clots, the maximum embolus size (mean, 1.19 [SD, 0.9] mm versus 2.16 [SD, 1.48] mm; P < .01) and total area of emboli (mean, 1.82 [SD, 2.73] versus 3.34 [SD, 3.2]; P = .01) were also lower with Solumbra than with SAVE. Clot characteristics may influence the efficacy of the thrombectomy technique. In occlusions caused by soft clots, complete retrieval into the distal aspiration catheters achieved higher rates of first-pass recanalizaton and lower embolization.

In vitro testing of a funnel-tip catheter with different clot types to decrease clot migration in mechanical thrombectomy.

Mechanical thrombectomy is the standard treatment for acute ischemic stroke in patients with large vessel occlusion and can be performed up to 24h after symptom onset. Despite high recanalization rates, embolism in new territories has been reported in 8.6% of the cases. Causes for this could be clot abruption during stent retrieval into the smaller opening of a standard distal access catheter, and antegrade blood flow via collaterals despite proximal balloon protection. A funnel-shaped tip with a larger internal diameter was developed to increase the rate of first-pass recanalization and to improve the safety and efficacy of mechanical thrombectomy. This in vitro study compared the efficacy of a funnel-shaped tip with a standard tip in combination with different clot compositions. Mechanical thrombectomy was performed 80 times for each tip, using two stent retrievers (Trevo XP ProVue 3/20 mm, 4/20 mm) and four different clot types (hard vs. soft clots, 0-24h vs. 72h aged clots). Significantly higher first-pass recanalization rates (mTICI 3) were observed for the funnel-shaped tip, 70.0% versus 30.0% for the standard tip (absolute difference, 32; relative difference 57.1%; P < .001), regardless of the clot type and stent retriever. Recanalization could be increased using harder Chandler loop clots versus softer statically generated clots, as well as 0-24h versus 72h aged clots, respectively. The funnel-shaped tip achieved higher first-pass recanalization rates than the smaller standard tip and lower rates of clot abruption at the tip. Clot compositions and aging times impacted recanalization rates.

Investigation of Current and Super‐Bore 088″ Treatment Strategies of Soft and Stiff Clots at Internal Carotid Artery and Middle Cerebral Artery Occlusion Sites in an In Vitro Thrombectomy Model

Background Various mechanical thrombectomy devices including stent retrievers (STRs), contact aspiration (CA) catheters, and balloon guide catheters (BGCs) are used in both isolation and combination for the treatment of acute ischemic stroke. A new generation of Super‐Bore 088″ aspiration catheters are being trialed clinically. We evaluated the in vitro revascularization performance of current and novel thrombectomy approaches in treating soft (red blood cell–rich) and stiff (fibrin/platelet‐rich) clots at internal carotid artery (ICA) and middle cerebral artery (MCA) occlusion sites. Methods National University of Ireland Galway Research Ethics Committee approved the study. Two human blood clot phenotypes were used to form ICA‐terminus (20‐mm) and MCA–M1 segment (10‐mm) occlusions in an in vitro thrombectomy model. Thrombectomy setups tested were CA: Millipede 088, SOFIA Plus+conventional guide catheter, SOFIA Plus+BGC and C ombination; Millipede 088+STR, SOFIA Plus+BGC+STR, SOFIA Plus+conventional guide catheter+STR. Ten replicates of each experiment were performed totaling 120 tests. Revascularization endpoints were first‐pass effect, final modified Thrombolysis in Cerebral Infarction (mTICI) 2c/3, and procedural‐related distal emboli. Results Millipede 088 CA achieved the highest first‐pass effect rate in ICA‐terminus (60%) and MCA–M1 segment (100%) occlusions and lowest number of procedural‐related distal emboli compared with all other device setups, followed by the combined Millipede 088+STR technique. Amongst the conventional techniques, higher first‐pass effect rates were observed with the combined technique using a BGC (40%) than 6F CA (20%) in ICA‐terminus occlusions whereas the reverse was seen in MCA–M1 segment occlusions, with 6F CA performing better than combined approaches (60% versus 50%). BGCs may provide a revascularization benefit in ICA‐terminus occlusions. Rates of first‐pass effect and final mTICI 2c/3 were better for stiff clots compared with soft clots for all treatment approaches at both occlusion sites. Conclusion Millipede 088 CA was the most effective technique for all clot types and occlusion locations. Across conventional techniques, CA seems to be more effective in MCA–M1 segment occlusions, while the combined technique performed better in ICA occlusions. Clot composition influences the success of each technique.

A new aspiration device equipped with a hydro-separator for acute ischemic stroke due to challenging soft and stiff clots.

Fragile soft clots and stiff clots remain challenging in the treatment of acute ischemic stroke. This study aims to investigate the impact of clot stiffness on the efficacy of thrombectomy devices and a new aspiration catheter with a hydro-separator. The Neurostar aspiration catheter has a novel hydro-separator technology that macerates clots by a stream of saline inside the catheter. The Neurostar catheter and two commercially available devices, the SOFIA aspiration catheter and Solitaire stent retriever, were tested in this study. We evaluated the efficacy of each device on clots with various stiffness in a simple in vitro model. We also assessed single-pass recanalization performance in challenging situations with large erythrocyte-rich clots and fibrin-rich clots in a realistic vascular model. We observed an inverse association between the clot stiffness and recanalization rates. The aspiration catheter, SOFIA ingested soft clots but not moderately stiff clots. When removing soft clots with the stent retriever, fragmentation was observed, although relatively stiff clots were well-integrated and removed. The Neurostar ingested soft clots similar to the aspiration catheter, and also aspirated stiff clots by continuous suction with hydro-separator. In the experiments with challenging clots, the Neurostar led to significantly higher recanalization rates than the stent retriever and aspiration catheter. The stiffness of the clots affected the efficacy of endovascular thrombectomy based on the type of device. The Neurostar catheter with hydro-separator resulted in better success rates than a commercially available aspiration catheter and stent retriever in this experimental model.

Novel Human Acute Ischemic Stroke Blood Clot Analogs for In Vitro Thrombectomy Testing.

Previous studies have successfully created blood clot analogs for in vitro endovascular device testing using animal blood of various species. Blood components vary greatly among species; therefore, creating clot analogs from human blood is likely a more accurate representation of thrombi formed in the human vasculature. Following approval from the Mayo Clinic institutional review board, human whole-blood and platelet donations were obtained from the blood transfusion service. Twelve clot analogs were created by combining different ratios of red blood cells + buffy coat, plasma, and platelets. Thrombin and calcium chloride were added to stimulate coagulation. Clot composition was assessed using histologic and immunohistochemical staining. To assess the similarities of mechanical properties to patient clots, 3 types of clot analogs (soft, elastic, and stiff) were selected for in vitro thrombectomy testing. The range of histopathologic compositions produced is representative of clots removed during thrombectomy procedures. The red blood cell composition ranged from 8.9% to 91.4%, and fibrin composition ranged from 3.1% to 53.4%. Platelets (CD42b) and von Willebrand Factor ranged from 0.5% to 47.1% and 1.0% to 63.4%, respectively. The soft clots had the highest first-pass effect and successful revascularization rates followed by the elastic and stiff clots. Distal embolization events were observed when clot ingestion could not be achieved, requiring device pullback. The incidence rate of distal embolization was the highest for the stiff clots due to the weak clot/device integration. Red blood cell-rich, fibrin-rich, and platelet-rich clot analogs that mimic clots retrieved from patients with acute ischemic stroke were created in vitro. Differing retrieval outcomes were confirmed using in vitro thrombectomy testing in a subset of clots.

Evaluation of challenges and limitations of mechanical thrombectomy using 3D printed neurovascular phantoms.

The mechanical thrombectomy (MT) efficacy, for large vessel occlusion (LVO) treatment in patients with stroke, could be improved if better teaching and practicing surgical tools were available. We propose a novel approach that uses 3D printing (3DP) to generate patient anatomical vascular variants for simulation of diverse clinical scenarios of LVO treated with MT. 3DP phantoms were connected to a flow loop with physiologically relevant flow conditions, including input flow rate and fluid temperature. A simulated blood clot was introduced into the model and placed in the Middle Cerebral Artery region. Clot location, composition (hard or soft clot), length, and arterial angulation were varied and MTs were simulated using stent retrievers. Device placement relative to the clot and the outcome of the thrombectomy were recorded for each situation. Angiograms were captured before and after LVO simulation and after the MT. Recanalization outcome was evaluated using the Thrombolysis in Cerebral Infarction (TICI) scale. Forty-two 3DP neurovascular phantom benchtop experiments were performed. Clot mechanical properties, hard versus soft, had the highest impact on the MT outcome, with 18/42 proving to be successful with full or partial clot retrieval. Other factors such as device manufacturer and the tortuosity of the 3DP model correlated weakly with the MT outcome. We demonstrated that 3DP can become a comprehensive tool for teaching and practicing various surgical procedures for MT in LVO patients. This platform can help vascular surgeons understand the endovascular devices limitations and patient vascular geometry challenges, to allow surgical approach optimization.

Cutting of blood clots – Experiment and smooth particle Galerkin modelling

This study investigates the cutting and removal of blood clots inside blood vessels using a high-speed rotary miniature cutting tool, which is inside and near the tip of a catheter with vacuum suction to deform and draw the soft clot inside the catheter tip for cutting and chip removal. The cutting forces at rotational speeds of 60,000, 90,000, and 120,000 rpm were measured to be 0.74, 0.59, and 0.36 N, respectively. A smooth particle Galerkin model was established, and the predicted cutting forces matched the experiment measurements with errors from 3% to 20%.

Amniotic fluid as a potent activator of blood coagulation and platelet aggregation: Study with rotational thromboelastometry

IntroductionPulmonary thromboembolism (PTE) is a leading cause of maternal death and frequently occurs during early puerperium. Amniotic fluid components are frequently observed in the maternal circulation in parturition; however, it currently remains unclear whether amniotic fluid contamination in maternal blood is related to the high incidence of PTE in early postpartum. ObjectivesTo examine the influence of amniotic fluid on blood coagulation and fibrinolysis systems with thromboelastometry. Materials and methodsTwenty-one pregnant women were recruited. We used whole citrated blood in ROTEM® (Tem Innovations GmbH, Munich, Germany), including the non-activated assay (NATEM), assessments for extrinsic (EXTEM) and intrinsic pathways (INTEM), fibrin polymerization (FIBTEM), and hyperfibrinolysis (APTEM), with amniotic fluid contamination, and measured the clotting time (CT), clot formation time (CFT), alpha, amplitude at 10 min (A10), maximum clot firmness (MCF), and lysis indices at 30 min (LI30) and 60 min (LI60). ResultsShort CT in all assays as well as short CFT, high alpha, and increased A10 and MCF in NATEM were observed with amniotic fluid contamination. A10 and MCF as well as LI30 and LI60 decreased in EXTEM. Decreased LI60 with the mixture of amniotic fluid was not improved by tranexamic acid in APTEM. ConclusionsAmniotic fluid accelerated thrombin production and activated platelet aggregation without inducing hyperfibrinolysis in whole blood. The activated tissue factor pathway with amniotic fluid produced soft and fragile clots due to its influence on platelets, which may be associated with, at least partly, the high incidence of PTE in early puerperium, particularly after cesarean section.

Relevance of hemolysis-induced tissue factor expression on monocytes in soft clot formation in alcohol-containing blood.

The fluidity of cadaveric blood is an important characteristic in the post-mortem examination of cases of asphyxial death. Although it is empirically known that soft blood clots are present in cadaveric blood containing alcohol, the relationship between such clots and blood alcohol is unclear. We addressed this issue through in vitro studies using blood collected from healthy volunteers. Assessment of global hemostasis by rotational thromboelastometry revealed that ethanol treatment enhanced the procoagulant activity of whole blood. However, ethanol inhibited epinephrine-induced platelet aggregation, whereas plasma levels of von Willebrand factor and the activity of coagulation factors VIII and IX were unaffected. In contrast, tissue factor (TF) activity was higher in plasma obtained from ethanol-treated whole blood than that in plasma from untreated blood. Ethanol induced hemolysis of red blood cells, and the consequent hemoglobin (Hb) release promoted de novo synthesis of TF in isolated monocytes, as determined by real-time reverse transcription PCR, western blotting, and flow cytometry. However, ethanol itself did not induce TF expression in monocytes. Given that TF activates the extrinsic coagulation pathway and amplifies hemostatic reactions, Hb-induced TF expression in monocytes might contribute to soft blood clot formation.

Pericellular plasma clot negates the influence of scaffold stiffness on chondrogenic differentiation.

Cell fate is influenced by the mechanical properties of cell culture substrates. Outside the body, cartilage progenitor cells express significant amounts of cartilage-specific markers on soft scaffolds but not on stiff scaffolds. However, when implanted in joints, stiff scaffolds show equivalent expression of markers as seen in soft scaffolds. This disparity in existing literature prompted our study. Our results suggest that encapsulation of cells in a soft plasma clot, present in any surgical intervention, prevents their perception of stiffness of the underlying scaffold, and hence the ability to distinguish between soft and stiff scaffolds vanishes. This finding would aid the design of new scaffolds that elicit cartilage-like biochemical properties while simultaneously being mechanically comparable to cartilage tissue.

Quantitative assessment of device–clot interaction for stent retriever thrombectomy

PurposeRapid revascularization in emergent large vessel occlusion with endovascular embolectomy has proven clinical benefit. We sought to measure device–clot interaction as a potential mechanism for efficient embolectomy.MethodsTwo different radiopaque clot...

Abstract TP261: Clot Integration Factor for in-vitro Quantification of Stent-retriever Configuration Using Cone-beam CT

Objective: Mechanical thrombectomy using stent-retriever technology provides acute ischemic stroke patients with beneficial treatment of emergent large vessel occlusion. Still, the disparity between recanalization rates and clinical outcomes calls for enhanced device designs and treatment strategies with better reperfusion efficiency. Intuitively, sufficient device integration with the embolus is pursued to maximize chances of first-pass success, thereby limiting clot fragmentation and intimal trauma during extensive clot manipulation. Our aim was to develop an imaging-based measure of device integration in reproducible phantom experiments that could help identifying differences in aspects of thrombectomy procedures that may be related to angiographic and clinical outcomes. Methods: Deployment variations of the Trevo(TM) ProVue/XP retriever were tested in an in-vitro model system that mimicked a MCA-occlusion with a silicone vascular replica and two visible clot models (soft elastic, and hard inelastic) with 8 trials/group. High-resolution cone-beam CT imaging was performed prior to retriever retraction. An image processing pipeline was devised that used level-set segmentation, path-tracing, and Steiner circumellipse fitting to extract and determine the interior volumes of the clot and the three visible wires. Clot Integration Factor (CIF) was calculated as the ratio of the volume of clot-device intersection to the clot volume. Results: Example of the device, its wires, and the clot: Average clot volumes were 90.4±12.2mm3. CIF was significantly different for two deployment variations when the device engaged a hard clot (difference between means, 95%CI=[0.003,0.187], p=0.043), but not a soft clot model (95%CI=[-0.152,0.263], p=0.567). Conclusion: In-vitro imaging-based quantification of clot integration can detect differences in deployment configuration relative to a clot, which may support procedural and design improvements.

Complementary CT Coronary Angiography after Negative Selective Coronary Angiography.

A 53-year-old male was admitted for typical acute chest pain. The ECG showed a mirror image of posterior myocardial ischemia. Initial biology was normal but cardiac markers (creatine kinase and troponin) rose later. Echocardiography did not reveal any hypokinetic myocardial segment. There was no left ventricular dysfunction or valvular disease. There was no pericardial effusion or aortic dissection image. This patient was treated as a “non-ST segment elevation myocardial infarction” (NSTEMI), also called subendocardial myocardial infarction. A selective coronary angiography (SCA) was performed the next day and after careful examination by several experts, no coronary lesion was detected. Left ventriculography was also normal. Cardiac MRI was then performed and revealed a late focal subendocardial enhancement, located in the mid infero-posterior myocardial segment (Fig. A, arrow). This lesion appeared to be ischemic, despite normal SCA. Computed tomography coronary angiography (CTCA) was finally done, showing a hypodense image, with also an ischemic aspect, in the same subendocardial area (Fig. B, arrow) as observed on MRI. Furthermore, CTCA detected tight luminal narrowing with hypodense material (soft atheroma or clot) in a circumflex branch (Fig. C, arrow), corresponding to the suspected ischemic territory. In this case, CTCA both confirmed ischemic etiology and identified culprit artery missed by SCA.

Risk of distal embolization with stent retriever thrombectomy and ADAPT

BackgroundThere is a discrepancy in clinical outcomes and the achieved recanalization rates with stent retrievers in the endovascular treatment of ischemic stroke. It is our hypothesis that procedural release of...

O-033 Aspiration Efficacy of Suction Catheter in the Management of Distal Embolization During Interventional Treatment of Acute Ischemic Stroke

IntroductionImproved recanalization rate and immediate flow restoration have been achieved by the latest clot retrieval (thrombectomy) systems in the acute ischemic stroke treatment. However, clot debris generated during mechanical thrombectomy...

Abstract W P16: Quantitative Analysis of Distal Emboli During Mechanical Thrombectomy With Stent-Trievers

Introduction: While the use of stentrievers has been shown to improve clinical outcomes compared with previous generation technology in the interventional treatment of stroke, there remains variability in clinical results. One contributor may be distal clot fragmentation during thrombectomy. Our goal is to assess various treatment strategies that can reduce the risk of distal embolization. Materials and Methods: Three different treatment strategies using stentrievers (Solitaire FR) included 1 Proximal flow control with a balloon guide catheter (BGC), 2 Thromboaspiration via a 5Fr distal access catheter (DAC) in the origin of the MCA, and 3 Thrombectomy through a conventional 6Fr conventional guide catheter (CGC). The vascular phantom included collateral circulation via PCom and ACom arteries and two different clot types were used( Stroke 2013;44:1396) . For each strategy and clot type, 8 replicate experiments were performed. Large clot fragments (&gt;1000μm) were separated from the effluent collected at each the ACA and MCA outlets and the longest dimension recorded. Particle size and number (&lt;1000μm) were measured with a Coulter counter. A cumulative distribution of clot fragments was made with a moving average of 10μm-wide bins centered at 0.2μm intervals across a range of 25-1000μm. Exponential decay functions were fit to the data and time-constants were calculated. Results: For visible fragments, &gt;1mm, both the use of the BGC and the DAC techniques produce fewer visible clot fragments (&gt;1000μm) as compared to CGC technique (p&lt;0.05, hard clot). For particulate sizes between 250-1000μm there was a trend towards a lower rate of hard clot embolic particulate with the DAC technique. In the size range of 25-250μm, the BGC produced less clot fragments than the DAC technique (p&lt;0.05, hard clot). In the &lt;25 μm group the BGC technique produced a lower rate of embolic particulates compared to the DAC or CGC technique (p&lt;0.05). All regressions had a coefficient of determination &gt;0.95. The BGC and DAC methods were found to have the shortest time-constants for hard and soft clots, respectively. Conclusion: Use of the BGC during a Solitaire FR thrombectomy is associated with statistically lower rates of distal emboli across a broad range of embolic particle sizes..

Limitations of using synthetic blood clots for measuring in vitro clot capture efficiency of inferior vena cava filters

The purpose of this study was first to evaluate the clot capture efficiency and capture location of six currently-marketed vena cava filters in a physiological venous flow loop, using synthetic polyacrylamide hydrogel clots, which were intended to simulate actual blood clots. After observing a measured anomaly for one of the test filters, we redirected the focus of the study to identify the cause of poor clot capture performance for large synthetic hydrogel clots. We hypothesized that the uncharacteristic low clot capture efficiency observed when testing the outlying filter can be attributed to the inadvertent use of dense, stiff synthetic hydrogel clots, and not as a result of the filter design or filter orientation. To study this issue, sheep blood clots and polyacrylamide (PA) synthetic clots were injected into a mock venous flow loop containing a clinical inferior vena cava (IVC) filter, and their captures were observed. Testing was performed with clots of various diameters (3.2, 4.8, and 6.4 mm), length-to-diameter ratios (1:1, 3:1, 10:1), and stiffness. By adjusting the chemical formulation, PA clots were fabricated to be soft, moderately stiff, or stiff with elastic moduli of 805 ± 2, 1696 ± 10 and 3295 ± 37 Pa, respectively. In comparison, the elastic moduli for freshly prepared sheep blood clots were 1690 ± 360 Pa. The outlying filter had a design that was characterized by peripheral gaps (up to 14 mm) between its wire struts. While a low clot capture rate was observed using large, stiff synthetic clots, the filter effectively captured similarly sized sheep blood clots and soft PA clots. Because the stiffer synthetic clots remained straight when approaching the filter in the IVC model flow loop, they were more likely to pass between the peripheral filter struts, while the softer, physiological clots tended to fold and were captured by the filter. These experiments demonstrated that if synthetic clots are used as a surrogate for animal or human blood clots for in vitro evaluation of vena cava filters, the material properties (eg, elastic modulus) and dynamic behavior of the surrogate should first be assessed to ensure that they accurately mimic an actual blood clot within the body.

Reduction in Distal Emboli With Proximal Flow Control During Mechanical Thrombectomy

To evaluate the impact of proximal flow control on efficacy and safety of mechanical thrombectomy in an in vitro middle cerebral artery occlusion. Three independent variables, including clot type, device (Merci Retriever, Solitaire FR, and Trevo devices), and use of a balloon guide catheter, were used to ascertain the impact of proximal flow control on the size and number of distal emboli generated during thrombectomy. Secondary end points were the recanalization rate and amount of flow restored. Use of the balloon guide catheter during thrombectomy of the fragile, hard clot significantly reduced the formation of large distal emboli with a diameter >1 mm, regardless of the device used (P<0.01). Applying aspiration via the balloon guide catheter in place of the conventional guide catheter resulted in a significant increase of flow reversal (P<0.0001). Prior to thrombectomy, deployment of the stent-trievers produced immediate flow restoration through the soft and hard clot occlusions, 69.2 ± 27.3 and 45.5 ± 22.8 mL/min, respectively, that was preserved after the balloon inflation because of collateral flow via the posterior communication artery. After deployment but before thrombectomy, no flow was restored when using the Merci Retriever. After thrombectomy, complete flow restoration was achieved in a majority of cases. The Merci Retriever required more thrombectomy attempts to achieve hard clot removal compared with the stent-trievers when the conventional guide catheter was used (1.5 versus 1.1). The risk of distal embolization was significantly reduced with the use of the balloon guide catheter.