eMedicine Specialties > Neurology > Neuro-vascular Diseases
Mechanical Thrombolysis in Acute Stroke
Updated: May 26, 2009
Introduction
At present, intravenous (IV) tissue-type plasminogen activator (tPA) is the only medical therapy approved for treatment of acute stroke in the United States. Almost 50% of patients treated with tPA in the trial by the National Institutes of Neurologic Disorders and Stroke (NINDS) achieved essentially full recovery.1 However, subgroup analyses of the NINDS data showed that patients with severe strokes had only an 8% likelihood of achieving clinically significant improvement with tPA.2 The poor outcome in these patients has inspired the search for acute-stroke treatments that are more effective than tPA.
One treatment involves the use of catheters to directly deliver a clot-disrupting or retrieval device to a thromboembolus that is occluding a cerebral artery. Mechanical thrombolytic devices can remove a clot in a matter of minutes, whereas pharmaceutical thrombolytics, even those delivered intra-arterially (IA), may take as long as 2 hours to dissolve a thrombus.3,4 This timesaving feature has encouraged the use of long treatment windows in trials of acute stroke treatments. In addition, IA delivered devices could potentially lower rates of intracranial hemorrhage (ICH) compared with IA pharmaceutical lytics.
A number of mechanical thrombolysis devices have entered clinical trials for treatment of acute stroke. These devices have used suction-creating saline jets, laser energy, ultrasound, a corkscrew-like apparatus and aspiration to treat strokes. Other mechanical approaches have not been assessed in clinical trials. One such method takes advantage of the suction created by pulling back on a syringe, and another uses a snare to retrieve a clot. Most devices are used in cerebral vessels that are 2-5 mm, and mechanical clot thrombolysis must be performed at an institution where angiography is available because catheters are used to deliver the device to the clot during angiography. This article reviews these devices and the known clinical safety data.
For related information see eMedicine article Acute Stroke Management.
Discontinued Study: AngioJet System
The AngioJet system (Possis Medical, Inc, Minneapolis, Minn) uses saline jets that are directed back into the catheter to create a low-pressure zone around the catheter tip, inducing suction (see Media files 1-2).
AngioJet catheter, shown with its saline jets activated. Courtesy of Possis Medical, Inc, Minneapolis, Minn.
Possis Neuro Catheter. Courtesy of Possis Medical, Inc, Minneapolis, Minn.
The clot is pulled into the exhaust lumen and removed from the vessel. Although the US Food and Drug Administration (FDA) has approved this device for use in arteriovenous dialysis grafts and fistulae and for the treatment of coronary arteries, saphenous vein grafts, and peripheral vessels, clinical trials for the treatment of acute stroke are no longer in progress.
The randomized Vein Graft AngioJet Study (VeGAS 2) trial was conducted to compare treatment with the AngioJet system with urokinase followed by percutaneous treatment to revascularize both native coronary arteries and saphenous vein bypass grafts in 349 patients.5 Patients receiving AngioJet treatment had in-hospital outcomes significantly better than those of the other patients, though 30-day event rates were similar in the 2 groups. However, the primary endpoints comprised a large number of events: stroke, death, myocardial infarction, target lesion revascularization, creatine kinase MB release, Thrombolysis in Myocardial Infarction (TIMI) blood-flow grade less than 3, and stenosis less than 50% of vascular diameter.
For the treatment of thromboemboli causing stroke, a device was developed to fit the size of the internal carotid artery (ICA). Two centers reported their experiences using the AngioJet system to treat ICA occlusion.6 In 3 patients, the device was used to debulk extensive ICA clots to allow for access to intracranial vessels. The thrombectomy was technically feasible, and clot burden was reduced in all patients. However, despite angiographic successes, clinical outcomes were poor. The authors postulated that these outcomes likely represented poor collateral flow in these patients.
Possis Medical, Inc designed a small device to allow treatment of thromboemboli in vessels other than the ICA. Safety and efficacy trials were in progress to investigate its use in occlusions of the M1 or M2 segment of the middle cerebral artery (MCA), carotid terminus, vertebral arteries, and basilar arteries within 6 hours of symptom onset. Between April 2000 and July 2003, 22 patients were enrolled in the Thrombectomy in Middle Cerebral Artery Embolism (TIME) trial. Two, and possibly 3, vessel perforations occurred, with subarachnoid hemorrhage. The company has stopped the trials.
Discontinued Study: Latis Laser Device
The Latis laser device (Latis, Inc, Coon Rapids, Minn) used laser energy to ablate clots. The device was evaluated in a safety and feasibility trial at 2 centers in the United States. Arteries 2-5 mm in diameter could be treated, including the ICA, M1 or M2 branch of the MCA, A1 branch of the anterior cerebral artery (ACA), basilar artery, posterior cerebral artery (PCA), and vertebral artery. Patients could receive treatment as late as 8 hours after symptom onset in the anterior circulation and within 24 hours in the posterior circulation. A preliminary account of the first 5 patients enrolled in the trial reported that the device could not be delivered to the clot in 2.7 Enrollment stopped at 12 patients. Although the catheter design was changed, an efficacy trial was not pursued.
Discontinued Study: Endovascular Photo Acoustic Recanalization Laser
The first mechanical thrombolysis device for which safety and feasibility results in patients with stroke were reported was the Endovascular Photo Acoustic Recanalization (EPAR) laser system (EndoVasix, Inc, Belmont, Calif).8 A laser power source generated energy for the system. The energy was delivered by means of fiberoptics to the tip of the catheter at the treatment site. Absorption of laser light by darkly pigmented materials (ie, the clot) occurred inside the 1-mm catheter tip, and the system was designed to minimize scattering of laser light. Absorption converted photo energy to acoustic energy, which then emulsified the clot inside the catheter tip (see Media files 3-5).
Endovascular Photo Acoustic Recanalization (EPAR) system. Image shows the laser energy source and catheter. Courtesy of EndoVasix, Inc, Belmont, Calif.
Endovascular Photo Acoustic Recanalization (EPAR) catheter tip. Courtesy of EndoVasix, Inc, Belmont, Calif.
Image of a cerebral vessel shows the Endovascular Photo Acoustic Recanalization (EPAR) catheter tip at the treatment site, in the thrombus. Courtesy of EndoVasix, Inc, Belmont, Calif.
Initial safety results for the EPAR system in the IA treatment of acute stroke were reported in February 20018 , and final results were published in 20043 . The trial was performed at 6 centers in the United States and in Germany. Patients received treatment for occlusions in the ICA, vertebral artery, basilar artery, ACA, MCA, and PCA. They were treated within 6 hours of stroke onset if they had a lesion in the anterior circulation and within 12 hours if they had a lesion in the posterior circulation.
The median baseline National Institutes of Health Stroke Scale (NIHSS) score was 19 (range, 6-39). In patients in whom the device was deployed, recanalization occurred in 12 (44%) of 27 who received EPAR treatment plus adjuvant therapy but only 4 (15%) treated with the device alone. ICH occurred in 2 (7%) patients: 1 (10%) of 10 treated with the device alone and in 1 (6%) of 17 who received an adjuvant in addition to the device. Thirty-eight percent of patients died.
The EPAR laser system showed acceptable safety, causing no complications during active lasering. However, 1 vessel ruptured during manual injection with a 1-mL syringe (instead of the recommended 3-mL syringe), causing the distal catheter to balloon and fatal vascular rupture. Although an international efficacy trial was approved to evaluate this device in the treatment of acute stroke, loss of funding stopped further clinical testing.
Ongoing Studies: EKOS Ultrasound Device
EKOS ultrasound
As its name suggests, the Ultrasound Thrombolytic Infusion Catheter (EKOS Corporation, Bothell, Wash) combines the use of a distal ultrasound transducer with infusion of a thrombolytic agent through the microcatheter (see Media files 6-8).
EKOS Micro Infusion Catheter. The catheter has a central lumen, an end-hole infusion port, and a 1.7-MHz ultrasound element. Courtesy of EKOS Corporation, Bothell, Wash.
EKOS catheter tip. Courtesy of EKOS Corporation, Bothell, Wash.
Schlieren photograph of EKOS device in operation. Courtesy of EKOS Corporation, Bothell, Wash.
Ultrasound changes the structure of the clot to temporarily increase its permeability while providing an acoustic pressure gradient to move the drug into the clot to speed its dissolution.
In a preclinical study, investigating the efficacy of the device in peripheral vascular occlusion, thrombi were induced in the bilateral superficial femoral arteries of 9 dogs.9 Although urokinase 5000 IU/kg was delivered to the vessels on both sides, the ultrasound transducer of the catheter was activated on only 1 side. After treatment, angiography showed good flow (ie, TIMI grade 2 or 3) in 9 (100%) of the ultrasound-treated segments and in 6 (67%) of the controls not treated (P = .058). Angioscopy and histopathology revealed more thrombi in the vessels that did not receive treatment than in those that did.
In human studies, results from the first 14 patients with acute stroke were reported in April 2000.10 In a safety and feasibility study, ultrasound was used with IA tPA infusion. The EKOS catheter was placed in the proximal portion of the clot. After a 2-mg bolus of tPA was injected through the catheter, the patient received a continuous infusion of IA tPA 0.3 mg/min to a maximum of 20 mg and simultaneous ultrasound transmission for as long as 60 minutes. One patient was treated with a total of 4 units of recombinant reteplase (Retavase) hand-injected over 60 minutes.
Five patients with MCA thrombi and 5 patients with carotid-T occlusions were treated within 6 hours of symptom onset, and 4 patients with posterior-circulation strokes were treated within 24 hours. The median NIHSS score was 19.5 (range, 9-27). TIMI grade 2-3 flow was attained in 8 (57%) of 14 patients in the first hour. The average time to recanalization was 46 minutes. No adverse events attributable to the catheter occurred.
After briefly considering a safety and feasibility trial using IA prourokinase in conjunction with the device, the EKOS Corporation pursued another trial with tPA. In this trial, called the Interventional Management of Stroke (IMS) II trial, patients were first treated with IV tPA at a dose of 0.6 mg/kg within 3 hours.11 Those with persistent clots received IA tPA in conjunction with ultrasound therapy. Indirect comparisons of the IMS II trial results with those in the NINDS tPA trial that included only those patients with an NIHSS of at least 10 and age 80 years or younger suggested that outcomes were at least as favorable at 3 months in the IMS II study. IMS III is comparing IV tPA treatment alone to lower-dose IV tPA plus one of a few intra-arterial treatments in patients in whom treatment is initiated within 3 hours.
Approved Devices: Merci Retrieval System and Penumbra System
The Merci Retrieval System
In 2004, the FDA approved the Merci Retrieval System, a corkscrew-like apparatus, to remove clots from vessels in patients experiencing an ischemic stroke (Concentric Medical, Inc, Mountain View, Calif) (see Media files 9-10).
Concentric MERCI Retriever embedded in a clot. Courtesy of Concentric Medical, Inc, Mountain View, Calif.
Clot retrieved from the basilar artery by using the MERCI Retriever. Courtesy of Concentric Medical, Inc, Mountain View, Calif, and Yu et al, 2003.
The corkscrew itself resides in the catheter tip, which shields it from the wall of the vessel until it is ready to be burrowed into the clot. Once lodged in the clot, the device and clot are withdrawn from the vessel. The Retriever has approval for use in patients with persistent vessel occlusion after IV tPA.
MERCI 1 study
Results for the first 28 patients treated within an 8-hour window as part of the Mechanical Embolus Removal in Cerebral Ischemia (MERCI) multicenter safety trial were published in 2004.12 Occlusions of the ICA, proximal segments of the MCA, basilar artery, or vertebral arteries were included. Successful recanalization (TIMI grades 2 or 3) occurred in 12 patients (43%) with the retriever alone and in 18 (64%) with additional IA tPA. No symptomatic ICH occurred.
MERCI study
Results of the full MERCI trial, in which the device was deployed in 141 of 151 patients, were published in 2005.13 The baseline median NIHSS score was 19. Recanalization with the device occurred in 68 patients (48%), which was significantly better than the rate in the placebo arm of the Prolyse in Acute Cerebral Thromboembolism (PROACT) II trial of patients with MCA occlusions (P <.0001)4 . Additional adjuvant therapy led to recanalization in 85 (60%) subjects. Symptomatic ICH occurred in 7 (8%) of 90 patients who were treated with the device alone and in 11 (8%) of 141 who received adjuvant treatment. Mortality rates in the 141 patients in whom the device was deployed was 44% (60 of 136), and the percentage with a modified Rankin score of 2 or less at 90 days was 28% (36 of 130).
Multi-MERCI study
The Multi-MERCI study included patients who had persistent clots after IV tPA treatment and incorporated a second-generation device, but otherwise it had similar inclusions to those in the MERCI trial.14,15
The final study results published in 2008 revealed that 29% (48/164) of patients received IV tPA prior to treatment with the Merci Retriever.15 The baseline median NIHSS score was 19 in the 164 patients. Recanalization occurred in 55% (90/164) with the device alone and in 68% (112/164) with the device plus adjuvant treatment. Symptomatic ICH occurred in 9.8% (16/164) of patients overall, although only 2.4% were PH2 hemorrhages based on the European Cooperative Acute Stroke Study (ECASS) classification system. (ECASS defines hemorrhages as either hemorrhagic infarctions (HI), type I with petechiae along the margin of the infarct and type II with more confluent petechia within the infarct, or parenchymal hematomas (PH),PH1 defined as a blood clot not exceeding 30% of the infarcted area with some mild space-occupying effect and 16 ) Symptomatic hemorrhages occurred in 10% (5/48) of those treated with IV tPA and the device, which was not different from the rate of 9.5% (11/116) in those that did not receive IV tPA. A favorable outcome, modified Rankin score of 2 or less, was seen in 36% (59/164) of patients at 90 days.
Multi-MERCI showed that outcomes were significantly better in those patients in whom the vessel opened compared with those in whom it did not.15 A favorable outcome was seen in 49.1% of revascularized patients versus 9.6% of those without revascularization. Mortality occurred in half as many patients with revascularization compared to no revascularization: 24.8% versus 51.9%.
Ongoing studies
The NINDS has funded a randomized trial of the Merci Retriever compared with medical therapy as long as 8 hours after symptom onset. This trial is called Magnetic Resonance and Recanalization of Stroke Clots Using Embolectomy (MR RESCUE). The effects of therapy will be stratified by the presence of a penumbra on MRI at randomization.
A trial that would not require MRI is also under consideration. This trial would randomize patients to the Merci Retriever or to medical management.
The Penumbra System
The FDA approved the Penumbra System (Penumbra, Inc, Alameda, Calif) in 2007 to open vessels in patients with ischemic strokes (See Media file 11). Patients who have received IV tPA can be treated. The device uses aspiration to remove the clot.
Penumbra aspiration. Courtesy of Penumbra, Inc., Alameda, Calif.
After an initial safety trial was completed in Europe17 , a study assessing the safety and efficacy of the system for recanalization of vessels was completed in the United States and Europe. Patients were included up to 8 hours after symptom onset. As in Multi-MERCI, patients could be treated if a persistent vessel occlusion was present after IV tPA, or if the INR was 3 or less. Initial results for the 125 patients were reported at the International Stroke Conference in New Orleans in February 2008. The baseline median NIHSS score was 18. The recanalization rate, measured for the target vessel, was 81.6%. Symptomatic intracranial hemorrhages occurred in 11.2%, although
Devices Not Evaluated in Acute-Stroke Trials
Snarelike devices
In anecdotal reports, interventionists used retrieval devices to remove thrombi from cerebral vessels. Snares, such as the Neuronet snare (Guidant Endovascular, Santa Clara, Calif), have been developed specifically for use in the treatment of strokes. These devices are simple in design and do not require the clot to be amenable to emulsification.
X-Sizer device
Yet another approach to mechanical clot disruption involves a device with small, moving blades at the catheter tip. This device, the X-Sizer device (EndiCor Medical, San Clemente, Calif), can be used to excise the thrombus and aspirate it. The device was being evaluated in randomized studies of coronary vessels and in a registry of patients with acute myocardial infarction. Although the manufacturer had modified the device for use in cerebral vessels, a safety and feasibility study was indefinitely suspended after only 1 patient was treated with the device in Europe.
Suction thrombectomy
This method of mechanical thrombolysis is one of the simplest. In this readily available technique, suction is applied with a syringe to remove thrombus in the ICA. It requires no other devices.
The use of suction thrombectomy in 2 patients with angiographically visualized ICA thrombus with TIMI grade 0 or 1 flow was reported in 1999.18 Patient 1 (NIHSS score, 12) was treated 17 hours after the onset of progressive right hemispheric symptoms, and patient 2 (NIHSS score, 23) was treated 5 hours after an abrupt onset of a severe neurologic deficit. A catheter with a large inner diameter (Brite Tip; Cordis Corporation, Miami, Fla) was placed in the symptomatic vessel and navigated over a guidewire into the thrombus. A 60-mL syringe was used to aspirate the thrombus. Each patient required angioplasty and stenting of carotid bifurcation stenosis and received daily aspirin and ticlopidine after the procedure. No complications occurred.
Both patients had excellent angiographic results, which showed minimal residual ICA stenosis and improved distal flow. Patient 1 had full functional recovery and a 3-month NIHSS score of 2, but patient 2 had a 3-month NIHSS score of 22.
Conclusions and Future Considerations
Clinical trials have shown that thrombectomy with mechanical thrombolysis devices is indeed feasible in the treatment of acute stroke. Although a number of such devices have been discontinued, some because of financial considerations, the Concentric Merci Retriever and Penumbra System have received FDA clearance. The EKOS ultrasound device continues to be evaluated in trials and other approaches are being considered.
The Merci Retriever has shown success in recanalizing vessels and better outcomes in those patients in whom the vessel was revascularized than in those in whom it was not. However, the true effect on the clinical outcomes of these patients with severe strokes would only be elucidated through a randomized trial. Concentric Medical has begun laying the groundwork for such a trial. In addition, the MR RESCUE trial is ongoing.
There is currently too little data available to compare the performance of the mechanical devices with IA lytics. Devices could potentially retrieve large clots that pharmaceutical agents are not able to lyse successfully. Large hemorrhages may occur less frequently with device use. However, the effects of such considerations on outcome is unclear. In the end, clots may best be treated with a combined approach using various devices, lytics, and antithrombotics.
Because few patients with stroke arrive at the hospital early enough to receive IV tPA, mechanical embolectomy potentially extends the treatment window. Patients who are not thrombolytic candidates, such as those that have had a recent surgical procedure, can be considered for treatment with mechanical embolectomy. In addition, patients treated with IV tPA may be considered for treatment of residual clot. We must consider the referral of potential treatment candidates for mechanical embolectomy to stroke centers that are equipped to perform the procedure.
Multimedia
 | Media file 1: AngioJet catheter, shown with its saline jets activated. Courtesy of Possis Medical, Inc, Minneapolis, Minn. |
 | Media file 2: Possis Neuro Catheter. Courtesy of Possis Medical, Inc, Minneapolis, Minn. |
 | Media file 3: Endovascular Photo Acoustic Recanalization (EPAR) system. Image shows the laser energy source and catheter. Courtesy of EndoVasix, Inc, Belmont, Calif. |
 | Media file 4: Endovascular Photo Acoustic Recanalization (EPAR) catheter tip. Courtesy of EndoVasix, Inc, Belmont, Calif. |
 | Media file 5: Image of a cerebral vessel shows the Endovascular Photo Acoustic Recanalization (EPAR) catheter tip at the treatment site, in the thrombus. Courtesy of EndoVasix, Inc, Belmont, Calif. |
 | Media file 6: EKOS Micro Infusion Catheter. The catheter has a central lumen, an end-hole infusion port, and a 1.7-MHz ultrasound element. Courtesy of EKOS Corporation, Bothell, Wash. |
 | Media file 7: EKOS catheter tip. Courtesy of EKOS Corporation, Bothell, Wash. |
 | Media file 8: Schlieren photograph of EKOS device in operation. Courtesy of EKOS Corporation, Bothell, Wash. |
 | Media file 9: Concentric MERCI Retriever embedded in a clot. Courtesy of Concentric Medical, Inc, Mountain View, Calif. |
 | Media file 10: Clot retrieved from the basilar artery by using the MERCI Retriever. Courtesy of Concentric Medical, Inc, Mountain View, Calif, and Yu et al, 2003. |
 | Media file 11: Penumbra aspiration. Courtesy of Penumbra, Inc., Alameda, Calif. |
Keywords
stroke, stroke treatment, mechanical embolectomy, mechanical thrombectomy, endovascular thrombectomy, intraarterial treatment of acute stroke, intra-arterial treatment of acute stroke, IA treatment of acute stroke, intraarterial thrombolysis, intra-arterial thrombolysis, IA thrombolysis, tissue-type plasminogen activator, tissue plasminogen activator, tPA, t-PA, mechanical thrombolysis in acute stroke
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| References |
References
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Berlis A, Lutsep H, Barnwell S, et al. Mechanical thrombolysis in acute ischemic stroke with endovascular photoacoustic recanalization. Stroke. May 2004;35(5):1112-6. [Medline].
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Smith WS. Safety of mechanical thrombectomy and intravenous tissue plasminogen activator in acute ischemic stroke. Results of the multi Mechanical Embolus Removal in Cerebral Ischemia (MERCI) trial, part I. AJNR Am J Neuroradiol. Jun-Jul 2006;27(6):1177-82. [Medline].
Smith WS, Sung G, Saver J, Budzik R, Duckwiler G, Liebeskind DS, et al. Mechanical thrombectomy for acute ischemic stroke: final results of the Multi MERCI trial. Stroke. Apr 2008;39(4):1205-12. [Medline].
Hacke W, Kaste M, Fieschi C, Toni D, Lesaffre E, von Kummer R. Intravenous thrombolysis with recombinant tissue plasminogen activator for acute hemispheric stroke. The European Cooperative Acute Stroke Study (ECASS). JAMA. Oct 4 1995;274(13):1017-25. [Medline].
Bose A, Henkes H, Alfke K, Reith W, Mayer TE, Berlis A. The Penumbra System: a mechanical device for the treatment of acute stroke due to thromboembolism. AJNR Am J Neuroradiol. Aug 2008;29(7):1409-13. [Medline].
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Further Reading
Keywords
stroke, stroke treatment, mechanical embolectomy, mechanical thrombectomy, endovascular thrombectomy, intraarterial treatment of acute stroke, intra-arterial treatment of acute stroke, IA treatment of acute stroke, intraarterial thrombolysis, intra-arterial thrombolysis, IA thrombolysis, tissue-type plasminogen activator, tissue plasminogen activator, tPA, t-PA, mechanical thrombolysis in acute stroke
