Treatment of Acute Stroke with Mechanical Clot Extraction
Abstract & Commentary
Source: Mayer TE, et al. Treatment of basilar artery embolism with a mechanical extraction device. Stroke. 2002;33:2232-2235.
Intravenous thrombolysis with tissue plasminogen activator (tPA) for acute stroke is limited by a short time window (less than 3 hours) and may not be effective when the burden of clot is large. Local thrombolysis with tPA by an intra-arterial (IA) route may be more effective for large thrombi, particularly in the basilar artery or in the distal internal carotid or proximal middle cerebral artery. IA thrombolysis may also be used in a wider time window such as up to 6 hours in the anterior circulation or perhaps 12-24 hours for the basilar artery. Use of the IA route also offers the possibility of using mechanical devices, limiting the necessary dose of thrombolytic, or eliminating the need for chemical lysis entirely. Although hemorrhages may still complicate strokes treated with mechanical techniques, the overall risk of ICH is significantly attenuated.
A number of different mechanical devices have been piloted in animal and human studies—all involving modifications of microcatheters capable of being navigated into the intracranial vasculature. These technologies follow 2 basic strategies: clot destruction or clot removal. Thrombi may be destroyed by the inflation of angioplasty balloons or the use of devices such as endovascular lasers or "angiojet" (pulsation) systems. Alternatively, clots may be "snared" with baskets or other cathteter tips designed to trap and extract thrombi from occluded vessels. Such retrieval systems represent an important advance because unlike with tPA or mechanical clot disruption, there is no significant risk of dangerous distal embolism. In the case of a mid-basilar thrombosis, for instance, propagation of clot fragments distally to the basilar tip following tPA often puts the vital thalamoperforator vessels at risk. In the middle cerebral artery system, showering of clot material distally into small cortical branches may produce clinically significant infarcts. With clot extraction, such complications are largely avoided.
In an extremely preliminary report, Mayer and associates present data on 5 patients with basilar artery thromboses treated with a device called "Neuronet." This nitinol self-expanding basket, delivered with a microcatheter, is capable of "loading up" thrombus and retrieving it from an occluded vessel. Five total patients were studied. The first 2 failed, requiring "rescue" tPA administration. In the subsequent 3 cases (Patients 3-5), clot retrieval was facilitated by the inflation of balloons in the vertebral arteries proximal to the site of occlusion. This produced a reversal of flow and allowed the clot to be removed. Maintenance of anterograde flow toward the clot would otherwise "keep it in place like a cork." Patients 3 and 5 achieved TIMI III flow with the Neuronet, while patient 4 did require tPA to achieve optimal recanalization. This patient had a small amount of residual clot at the basilar tip despite a total of 3 attempts at retraction maneuvers. Overall, 3 out of 5 patients had good clinical outcomes with 2 remaining severely disabled. These clinical results would be considered superior to those seen among historical controls suffering from basilar thromboses.
Commentary
This study, though limited, represents important pilot data. Mechanical clot retrieval appears to be safe and effective. Additional reports are sure to follow, including some from our own center. In conjunction with the interventional neuroradiology group at Cornell, our Stroke Service has been fortunate to participate in the MERCI, Concentric Retriever Trial. In Phase I, 29 patients have been treated with a nitinol helical coil designed to screw into thrombi and extract them in a manner similar to that used with "Neuronet." There were no device related complications in Phase I of MERCI and the Phase II study is currently in preparation. —Alan Z. Segal
Dr. Segal, Assistant Professor, Department of Neurology, Weill-Cornell Medical College, Attending Neurologist, New York Presbyterian Hospital, is Assistant Editor of Neurology Alert.
In an extremely preliminary report, Mayer and associates present data on 5 patients with basilar artery thromboses treated with a device called Neuronet.
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