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New Generation Thrombectomy Device Reported to be Safe, Effective

SAN FRANCISCO —A new generation mechanical thrombectomy device seems to achieve slightly better recanalization rates than the first generation Mechanical Embolus Removal in Cerebral Ischemia (MERCI) devices, researchers reported here in February at a latebreaking session at the 2007 International Stroke Conference sponsored by the American Stroke Association.

The results also suggest that the new MERCI L5 device can be used safely in conjunction with tissue plasminogen activator (tPA) to achieve even greater restoration of blood flow in patients, said Wade S. Smith, MD, PhD, professor of neurology at the University of California-San Francisco, and principal investigator of the international Multi- MERCI trial.


In a single-arm prospective multicenter study of 164 patients, the recanalization rate with the L5 device was 57.3 percent. When optional adjunctive therapy with tPA was allowed, the recanalization rate reached 69.5 percent, “among the highest in any major acute ischemic stroke trial,” he said.

Of note was that the recanalization rates trended a nonsignificant 9 percent higher than the rate in the original MERCI trial, which used older generation X5 and X6 devices, he said.


Dr. Wade S. Smith said that due to better recanalization and more experienced operators, “We had better outcomes and lower mortality in Multi-MERCI,” the new generation mechanical thrombectomy device.

Due to both better recanalization and more experienced operators, “we had better outcomes and lower mortality in Multi-MERCI,” Dr. Smith said.

Made by Concentric Medical Inc., which funded the studies, the MERCI Retriever was approved for use in the acute treatment of stroke in 2004 based on a study that showed the device significantly restored patency within eight hours of stroke symptom onset in patients ineligible for tPA (Stroke 2005;36:1432–1438).

Dr. Smith noted that the first generation X5 and X6 devices have a flexible, tapered nickel titanium wire with a helical distal tip that can be deployed intra-arterially to entrap and retrieve large vessel clots within the brain.

The L5 version incorporates a cylindrical helix with attached filaments to improve securing the clot during retrieval.

The Multi-MERCI trial included patients with acute, large-vessel intracranial, basilar, or vertebral strokes treated at 15 hospitals in the US and Canada. After the first 33 patients were enrolled, physicians were instructed to use the new generation L5 device first; subsequent passes could be made with L5 or X5 and X6 models.

To be eligible, patients had to have a National Institutes of Health Stroke Scale (NIHSS) score of 8 points or higher. [The NIHSS offers parameters for assessing disability post-stroke. The lower the NIHSS, the less disability there is; scores 22 and over are considered severe neurologic disabilities.] Also, treatment had to be initiated within eight hours of stroke symptom onset, which Dr. Smith noted is beyond the three-hour treatment window for tPA.

Pretreatment with intravenous tPA was allowed; physicians were also allowed to give adjuvant intra-arterial tPA if the patient was treated within six hours of symptom onset.

The mean age of the patients, 57 percent women, was 68 years. The site of the vascular occlusion was the middle cerebral artery in 60 percent, intracranial carotid or intracranial carotid bifurcation vessels in 32 percent, and vertebrobasilar in 8 percent.

Eighty percent of all patients were first treated with the L5 device, and 20 percent were treated exclusively with the older X series.


Once the location of the clot has been identified using angiography, the Merci Balloon Guide Catheter is inserted through a small incision in the femoral artery in the groin. Under X-ray guidance, the Merci Balloon Guide Catheter is maneuvered up to the carotid artery in the neck, a guidewire and the Merci Microcatheter are deployed through the Balloon Guide Catheter and then placed just beyond the clot. The physician then uses the Merci Retriever device to engage and ensnare the clot. Once the clot is captured, the Merci Balloon Guide Catheter is inflated to temporarily arrest forward flow while the clot is being withdrawn. The clot is pulled into the Merci Balloon Guide Catheter and completely out of the body. The balloon is then deflated, and blood flow is restored.

The median time from symptom onset to groin puncture was 4.2 hours, and the median duration of the procedure was 1.6 hours for an average of three attempts to remove the clot.

Twenty-nine percent of the patients had been pretreated with tPA, “which tells us that tPA alone was not working,” Dr. Smith said.

The overall mortality rate was 34 percent; in contrast, it was 44 percent in the MERCI study, he said. “Mortality appears to drop, but we have not proven we lowered mortality,” Dr. Smith stressed. “For that we need a randomized clinical trial.”

As for safety, clinically evident complications of the procedure occurred in 5.5 percent of patients. Thirty-six percent of patients had favorable outcomes, that is, only slight disability as defined as a modified Rankin Scale score of 2 points or less; in the MERCI trial, 28 percent did.

When outcomes were considered a function of recanalization, 49.1 percent of patients who were recanalized had good outcomes – they had less disability as defined by Rankin score — compared with 9.6 percent who were not recanalized.

Symptomatic intracranial hemorrhage, defined as a decline in NIHSS of 4 points or more or any blood on postprocedure CT, occurred in 9.8 percent of patients. Asymptomatic ICH occurred in 30.5 percent of patients. Dr. Smith said there was no excess hemorrhage in patients treated with tPA. ”There has been a paradigm shift in how strokes are treated. When tPA doesn't work, we can try to open the vessel mechanically. In terms of clinical practice, I think the device is being rapidly adopted,” Dr. Smith said.


Other researchers commented that while the trials are important steps toward proving the efficacy of the device, a randomized controlled trial pitting the retriever against tPA is still needed.

Werner Hacke, MD, PhD, professor and chairman of the department of neurology at the University of Heidelberg in Germany, said his institution sometimes uses the device in patients who have failed or who are not candidates for tPA. But before it can be considered for routine use, “there must be an adequately powered trial with a control group to show its superiority,” he said.


Dr. Werner Hacke said that before the new device can be considered for routine use, “there must be an adequately powered trial with a control group to show superiority.”

American Stroke Association spokesperson Robert J. Adams, MD, Presidential Distinguished Chair, Regents and professor of neurology at the Medical College of Georgia, in Augusta, said that Multi-MERCI “is an important step to show that the device is safe and can be used with thrombolytics.”

But until a randomized controlled trial is performed, he said he “would only use it in a compassionate way – that is, someone who had a MCA [middle cerebral artery] occlusion with a large clot who I could get into the hands of a skilled operator in a short amount of time.”


✓ The new MERCI L5 device can be used safely in conjunction with tissue plasminogen activator to achieve even greater restoration of blood flow in patients, according to data presented at the International Stroke Conference.


• Smith WS, Sung G, Marks MP, et al., for the MERCI Trial Investigators. Safety and efficacy of mechanical embolectomy in acute ischemic stroke: results of the MERCI trial. Stroke 2005;36:1432–1438.