Mechanical Thrombolysis

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Mechanical thrombolysis as a primary or the sole therapy for acute ischemic stroke is not recommended at this time, except on a compassionate-use basis. This method of thrombolysis may be indicated in cases where standard IA thrombolysis has failed to achieve recanalization. Lesions in approximately 50% of patients are resistant to IA chemical thrombolysis.68,71 This failure of pharmacological agents in the setting of tenacious clot may be related to site of occlusion, heterogeneous composition of the clot, and underlying atherosclerotic stenosis. Although ranges are wide and variable, lower rates of recanalization are associated with chemical thrombolysis of acute cervical or intracranial ICA occlusions than with distal MCA branch occlusions. In addition, occlusive lesions of the vertebrobasilar artery territory are thought to be more atherothrombotic in nature than MCA occlusions, which may be more embolic.71,72 As a result, device selection may depend on the occlusion site as well as the vascular pathology.

Another indication for mechanical thrombolysis may be for patients who have missed the 3-hour window. Currently, the Mechanical Embolus Removal in Cerebral Ischemia (MERCI) trial is evaluating the safety and recanalization rate of the Concentric Retriever System (Concentric Medical, Mountain View, CA).73 Inclusion criteria include diagnosis of acute ischemic stroke; angiographic demonstration of occlusion in the ICA, M1 segment of the MCA, or BA; contraindications for intravenous t-PA; or patients who present after the 3 hour window in whom treatment can be initiated within the 8-hour window. Further studies need to be performed to evaluate the efficacy and therapeutic time window of these mechanical thrombolysis procedures. Basic Mechanical Thrombolysis Techniques

The authors have performed mechanical thrombolysis by using snares, angioplasty balloon catheters, microwires, microcatheters, and stents.38,74 A 6-French guide catheter is placed in the ICA or VA proximal to the lesion. In large vessels such as the ICA, proximal M1 segment of MCA, and BA, angioplasty was performed using coronary balloons. The diameter of the balloon is undersized in reference to the diameter of the adjacent portion of the occluded vessel. Angioplasty balloon catheters used by the authors for mechanical thrombolysis have included the Cross Sail (Guidant, Advanced Cardiovascular Inc, Temecula, CA), Open Sail (Guidant, Advanced Cardiovascular Inc), or Ninja (Cordis Neurovascular, Miami Lakes, FL). In smaller vessels such as the distal MCA (M2 and M3) segments, anterior cerebral artery, and posterior cerebral arteries, a microwire, microcatheter, or a 4-mm snare (Amplatz Goose-Neck Microsnare, Microvena, White Bear Lake, MN) can be used.

A microwire (.014 inch) is introduced into a microcatheter (2.3 French), and the complex is coaxially advanced through the 6-French guide catheter to the site of the occlusion. In smaller vessels, the lesion can be crossed multiple times with a microwire or microcatheter to achieve mechanical disruption of the clot.75 If a snare is used for mechanical thrombolysis, the lesion is crossed with a microwire and then by the microcatheter. The microwire is exchanged with a snare. The authors have made multiple passes with a snare through the occluded segment to disrupt the thrombus (Fig. 2). Chopko et al. have used a snare for clot retrieval.76 In this instance, the snare is gently tightened around the clot, and the microcatheter and guide catheter are withdrawn as a unit. In larger vessels, after the microcatheter is advanced across the lesion, the microwire is exchanged with an exchange wire. The microcatheter is removed, and a balloon catheter is advanced over the exchange wire, which facilitates balloon and stent navigation (Fig. 3). It is important not to oversize the balloon or the stent, which may lead to dissection or rupture of the affected vessel.

Clot Retrevial Devices

Among the new devices for thrombolysis are an ultrasound infusion microcatheter, a laser-driven thrombectomy device, and suction and rheolytic thrombectomy catheters. Preliminary experience with a unique ultrasound infusion microcatheter (EKOS, Bothel, WA) suggests that the technique is safe and yields favorable recanalization rates.77 In this technique, the catheter is placed within the thrombus and activated to produce ultrasonic resonance that agitates the thrombus and thereby facilitates the action of the thrombolytic agent.

In animal models of stroke, laser technology using Argon and Nd:Yag (Neodymium:yttrium aluminum garnet) radiation has demonstrated destruction of atheromatous plaque.78 This technique leads to vaporization of fresh thrombus and plaque without producing significant emboli. However, perforation of the artery wall is a major concern. A pulse-dye laser is unique in that it is tuned to hemoglobin absorption peak. This technique may minimize energy absorption in the vessel wall and allow photoacoustic mechanical disruption of the thrombus. These lasers may be attached to the microcatheter and navigated into the site of occlusion. Further research is underway.

Lutsep et al. reported successful recanalization with suction thrombectomy in three patients with ischemic stroke related to cervical ICA occlusion.79 In this technique, a 7-French guide catheter was navigated over a wire into the proximal third of the thrombus. A 60-ml syringe was used to aspirate the thrombus. The guide catheter was moved in and out of the thrombus several times before slowly being withdrawn to allow for complete removal of the thrombus. This technique may be limited to occlusions in the petrous segment of the ICA.

Another endovascular thrombectomy device is the AngioJet (Possis Medical, Inc, Minneapolis, MN).80 High-pressure saline jets are directed into the primary evacuation lumen of this thrombectomy catheter to create a hydrodynamic vortex that fragments adjacent thrombus and draws it into the recovery lumen. The use of this device for intracranial thrombectomy is being evaluated in ongoing trials.

Merci Clot Retriever

The Concentric MERCI (Mechanical Embolus Removal in Cerebral Ischemia) Retrieval System is a corkscrew-like apparatus designed to remove clots from vessels in patients with large vessel embolic strokes . The device have a corkscrew memory shape when deployed outside the delivery catheter. Once the device is deoplyed within the clot, it is retrieved into the catheter, and both are removed from the patient’s vessel. The Retriever has received approval from the US Food and Drug Administration (FDA) for use in patients with persistent vessel occlusion after IV tPA. In a study of patients with ischemic stroke, recanalization occurred in 55% of patients who were treated with a MERCI device alone and in 68% of patients who were treated with a MERCI device plus adjuvant treatment. Symptomatic ICH occurred in 9.8% (16/164) of patients overall, and a favorable outcome, (a modified Rankin score of 2 or less), was seen in 36% of patients at 90 days. A favorable outcome was seen in 49.1% of revascularized patients, versus 9.6% of those without revascularization. The mortality rate in patients with revascularization was approximately half that of patients with no revascularization (24.8% versus 51.9%, respectively).

Pneumbra Clot Retrevial

The Pneumbra clot retrieval device has been approved in the United States for the last several years. The retrieval device work by advancing large catheters into the intracranial circulation where the clot is broken up with a separator and aspirated through a negative pressure suction system. This technique has been proven to be effective in multiple clinical studies including the Pivotal trial in a multicenter trial. Post procedure 81.6% of the targeted occluded vessels were revascularized (TIMI 2&3). This reflected to mortality rate of 32.8% at 90 days with 25% have a modifid Rankin Scale score ≤ 2.

Solitaire Stent Retrevial

The SWIFT study aimed to show that the Solitaire was not inferior to the Merci device and was safe and effective in acute ischemic stroke patients requiring mechanical thrombectomy. It was a randomized controlled trial with blinded primary endpoint ascertainment. Patients randomized were seen within 8 hours of symptom onset, and were ineligible for or had failed tPA. SWIFT was stopped early because of robust results. The study population of 144 patients was enrolled from 18 sites across the United States. Patients were randomly assigned to treatment with the Solitaire device (n = 58) or Merci device (n = 55). The 2 arms were similar in age, pretreatment NIH Stroke Scale score, onset to treatment time, and 13 additional demographic and medical history variables. The primary efficacy outcome — successful recanalization without symptomatic intracranial hemorrhage — was achieved more often in the group treated with Solitaire than with Merci. The endpoint was met by 60.7% of the Solitaire group vs. 24.1% of the Merci group according to the blinded core laboratory results. Based on investigator determination, the recanalization rates were 83.3% and 48.1%, respectively (P < .0001).

Physcian and Patient Education

Chemical and mechanical approaches for IA thrombolyses are promising interventions in acute ischemic stroke. The safety and efficacy of IA thrombolysis within the 6-hour time window from symptom onset have been demonstrated in major randomized trials as well as case series. Patients with “brain attack” must be expeditiously transferred to institutions having the personnel and resources to provide therapies for the treatment of acute ischemic stroke and be evaluated to determine their eligibility for such therapies. Time is critical in these patients, regardless of the therapy chosen. Further studies need to be conducted regarding the efficacy and safety of combination intravenous and IA therapy. Newer fibrinolytic agents and mechanical devices may allow faster recanalization, but the safety of these agents and devices requires further evaluation. The precise role and the limits of newer imaging modalities, such as multimodal MR imaging, need to be defined to aid in selection of candidates for thrombolysis. Finally, physicians need to assume a pivotal role in educating the public about stroke prevention and treatment locally and nationally. Through the combined efforts of health care professionals, the general public, the American Heart Association, the National Stroke Council, and local and federal governments, management of stroke will improve in the future.

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