Endovascular Thrombectomy

Mechanical thrombectomy is a promising novel technique in interventional stroke treatment. The devices differ with regard to where they apply force on the thrombus, taking either a proximal approach with aspiration devices (see section on thromboaspiration below) or a distal approach with basket- or snare-like devices. A study comparing the effectiveness of these two approaches (Vasco35 vs. Catch device) in a swine stroke model demonstrated that the proximal device allowed fast repeated applications with a low risk of thromboembolic events (3% vs. 26%; OR 11.3, 95% CI 1.35-101.6) and vasospasm, but significantly lower success rates in retrieving thrombus than the distal device (39.4% vs. 82.6%; OR 7.3, 95% CI 2.0-26.4). The rate of embolic events with the distal device could be significantly reduced by employing the use of a proximal balloon occlusion.79 Balloon occlusion with aspiration to promote flow reversal also facilitates clot extraction.14

The Concentric Retriever (Concentric Medical Inc., Mountain View, CA), a flexible, nitinol wire with helical tapering coil loops (X5 and X6) that is used in conjunction with a balloon guide catheter (8 or 9 French) and a microcatheter, is the only device currently approved by the FDA for the endovascular treatment of stroke patients (Fig. 4.3).13 The second-generation devices (L5 and L6) differ from the X devices by the inclusion of a system of arcading filaments attached to a nontapering

FIGURE 4.3 Sixty-two-year-old left-handed female who presented with left hemiplegia, right gaze deviation, and aphasia 5 hours after an elective thyroidectomy. Right internal carotid artery (RICA) angiogram demonstrated occlusion of the right M1 segment just distal to the origin of the anterior temporal artery (a and b). RICA roadmap images demonstrating successful deployment of the Concentric Retriever within the clot (arrow c). Note the torque in the system when the clot is pulled back (arrow d) and the guide catheter balloon inflated (double arrows d). Small fragments of clot are shown (e).

FIGURE 4.3 Sixty-two-year-old left-handed female who presented with left hemiplegia, right gaze deviation, and aphasia 5 hours after an elective thyroidectomy. Right internal carotid artery (RICA) angiogram demonstrated occlusion of the right M1 segment just distal to the origin of the anterior temporal artery (a and b). RICA roadmap images demonstrating successful deployment of the Concentric Retriever within the clot (arrow c). Note the torque in the system when the clot is pulled back (arrow d) and the guide catheter balloon inflated (double arrows d). Small fragments of clot are shown (e).

FIGURE 4.3 (Continued) Final RICA angiogram demonstrated complete recanalization of the M1 segment of the right middle cerebral artery (f and g). CT performed 24 hours after the procedure demonstrated only a small area of hypoattenuation in the right insular region (h). Schematic drawing demonstrating how the Concentric Retriever engages and retrieves the intraluminal clot (i).

helical nitinol coil that has a 90° angle in relation to the proximal wire component. Third-generation devices (K devices), with a smaller profile that may allow for clot retrieval from more distal vessels, are currently being tested. This embolectomy system has been systematically studied in the MERCI and Multi-MERCI trials, which were discussed above.

The Neuronet device (Guidant Corp., Santa Clara, CA) is a microguidewire-based laser-cut nitinol basket open proximally with the crisscrossing basket portion tapering to a shapeable platinum-tipped wire. This device has been success-

fully used to retrieve intracranial clots, , , and is currently being tested in a European trial. The Catch device (Balt Extrusion, Montmorency, France) is a distally closed, self-expanding nitinol cage that has also been used for thrombectomy with promising results.80

The Phenox Clot Retriever consists of a metallic core made from a wire compound surrounded by a dense palisade of perpendicularly-oriented stiff polyamide microfilaments trimmed in a conical shape, which have an increasing diameter distally and are resistant to unraveling. The device is molded to the body of a 0.010-inch microguidewire. It is introduced into the target vessel through a 0.021-inch or 0.027-inch microcatheter, deployed distally to the thrombus, and slowly pulled back under continuous aspiration via the guiding catheter. Only two cases using this device have been reported thus far, including a case demonstrating recanalization of a Rolandic MCA branch.81 The Attracter-18 device (Target Therapeutics, Fremont, CA) is another fiber-based retriever device that has been successfully used to recanalize an occluded superior division branch of the left MCA refractory to IA thrombolytic treatment.82

The In-Time Retriever (Boston Scientific, Natick, MA) has four to six wire loops and tends to bow when opened but has no specific opening to capture the embolus. This device has been successfully used in a case of an MCA occlusion resistant to thrombolytics and balloon angioplasty,83 as well as in cases of basilar occlusion.70 The TriSpan (Boston Scientific, Natick, MA), a neck bridge device consisting of three nitinol loops originally designed to treat wide-necked aneurysms, has also been used to treat basilar occlusions.70

Other snare devices that potentially can be used for embolectomy include (1) the Alligator Retrieval Device, which is a retriever with grasping jaws attached to the tip of a flexible wire designed to be used in conjunction with 0.21-inch micro-catheter84; and (2) the EnSnare device, which has a tulip-shaped, three-loop design that opens distally. These devices, which are approved for foreign body removal/coil retrieval, have not been reported in embolectomy for stroke treatment.

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