Report from International Stroke Conference: Merci device plus tPA unblocks 68% of clogged intracranial arteries

February 14, 2007

Improved device performance and growing user experience are credited for a nine percentage point increase in successful recanalization following ischemic stroke. The improved rate over an earlier trial was reported Feb. 2 in the final results of the prospective 15-center Multi-Merci clinical trial of mechanical clot retrievers that restore intracranial blood flow after stroke.

Improved device performance and growing user experience are credited for a nine percentage point increase in successful recanalization following ischemic stroke. The improved rate over an earlier trial was reported Feb. 2 in the final results of the prospective 15-center Multi-Merci clinical trial of mechanical clot retrievers that restore intracranial blood flow after stroke.

Principal investigator Dr. Wade S. Smith reported that new L5 and L6 Merci clot retrievers achieved complete recanalization of occluded intracranial arteries for 55% of 111 acute stroke patients in the single-arm trial. Smith, a professor of neurology at the University of California, San Francisco, announced that the success rate rose to 68.3% when tPA thrombolyis was performed immediately after attempted mechanical extraction. Final results were presented at the American Stroke Association's 2007 International Stroke Conference in San Francisco.

The intravascular Merci retrieval systems are designed to address the most morbid forms of ischemic stroke originating from clots lodged in the vertebrovascular system, Smith said. About 60% of the treated thrombi in the Multi-Merci trial resided in the middle cerebral artery, 32% were in the intracranial artery or carotid T, and 8% were found in the vertebrobasilar artery.

The Merci system consists of a balloon guide catheter, guidewire, and microcatheter. The guide catheter, inserted percutaneously in the femoral artery, is maneuvered under fluoroscopic guidance to the internal carotid artery and through the clot. The microcatheter with a corkscrew tip in models X5 and X6 is deployed from the hollow guide catheter distal to the obstruction. Ideally, the thrombus is snagged and removed when the catheter is pulled from the vessel.

The typical procedure in the Multi-Merci trial involved three passes through the thrombus with the device. Average procedure time was 1.6 hours.

Models X5 and X6 received FDA 510(k) clearance for U.S. sale in August 2004 after the initial Merci trial involving 141 patients found that the device successfully recanalized 48% of vessels when used alone and 60% when tPA thrombolysis was performed immediately after extraction.

In contrast to the X5 and X6, the tip of the L5 consists of a tightly wound coil and thin fibers loosely strung from the tip to an anchor point several centimeters down the catheter. The L6 features a complex coil design.

FDA 510(k) clearance for the L5 was secured Feb. 5. The Centers for Medicare and Medicaid Services established an ICD-9 procedure code (39.74) for Merci retrievers in October 2006. Medicare will pay about $23,000 for the procedure, according to the American Society of Interventional and Therapeutic Neuroradiology. The Merci system was developed by Concentric Medical of Mountain View, CA.

The Multi-Merci trial of the L5 and L6 produced an encouraging, though not statistically significant, improvement from the X5 and X6 Merci trial. The nine percentage point higher recanalization rate, observed with and without follow-up thrombolysis, may reflect improved recanalization and more user experience with the procedure, Smith said.

The improved clot-extracting power of the L5 and L6 may explain the significant improvement in mortality rates compared with the X5 and X6 devices. Overall, about 34% of the patients treated in the Multi-Merci trial died in the 90 days after stroke onset, compared with 44% in the Merci trial.

Although the Multi-Merci trial was not designed to study mortality, slightly more than half (51.9%) of the patients without successful recanalization died, compared with slightly less than one-quarter (24.8%) who underwent successful revascularization. About 36% of the patients in the Multi-Merci trial achieved a favorable outcome as defined by a Rankin score of 2 or less.

"If you look at this graphically and divide it by vessel recanalization, as we showed before in Merci, there was a dramatic increase in the percentage of good outcomes if you opened the vessel and a 25% absolute risk reduction in morality," Smith said.

Evidence of intracranial hemorrhage appeared in follow-up CT interpreted by blinded readers in 16 patients, or 9.8% of the cases. Some cases were clearly type 1 or 2 hemorrhagic infarctions that are common in patients with revascularization therapy, Smith said.

Microcatheter perforation was responsible for one of the sizable bleeds. Only four of the cases (2.4%) were symptomatic PH2 hemorrhages, he said.

For more information from the Diagnostic Imaging archives:

Reporter from International Stroke Conference: MRI outperforms CT for initial stroke evaluation

Stenting gives uneven aid to patients at risk of stroke

Perfusion CT in acute stroke patients

The window expands for more effective stroke treatment