MERCI
Safety and Efficacy of Mechanical Embolectomy in Acute Ischemic Stroke: Results of the MERCI Trial
Clinical Question
To investigate the safety and efficacy of the Merci Retriever device for mechanical embolectomy to restore vascular patency in patients with acute ischemic stroke within 8 hours of symptom onset who are ineligible for intravenous tissue plasminogen activator (tPA).
Study Overview
Objective
To test the safety and efficacy of the Merci Retriever, a mechanical embolectomy device, in restoring blood flow in patients with acute large vessel occlusion stroke within 8 hours of onset who were ineligible for IV tPA.
Study Summary
- The device successfully recanalized the occluded artery (TIMI II/III flow) in 46% of patients (ITT), significantly better than an 18% historical control rate (p<0.0001).
- Successful recanalization was strongly linked to better outcomes: 46% of recanalized patients had a good outcome (mRS ≤2 at 90 days) vs. 10% of non-recanalized patients.
- Mortality was also lower with recanalization (32% vs. 54%).
Intervention
Mechanical embolectomy using the Merci Retriever device within 8 hours of stroke symptom onset in patients ineligible for IV tPA. Follow-up was 30 days in Part I; Part II added NIHSS/mRS assessments up to 90 days.
Bottom Line
The Merci Retriever device successfully restores vascular patency in a significant proportion of acute ischemic stroke patients with large vessel occlusions who are ineligible for intravenous tPA. Successful recanalization is strongly associated with substantially improved neurological outcomes and reduced mortality at 90 days.
Major Points
- The MERCI trial was a prospective, single-arm, multicenter study involving 151 patients with acute large vessel occlusion stroke presenting within 8 hours of onset who were ineligible for intravenous tPA.
- The primary efficacy outcome, vessel recanalization (TIMI II or III flow), was achieved in 46% of patients on an intention-to-treat basis, which was significantly higher than the 18% historical control rate from the PROACT-II trial (P<0.0001).
- Patients with successful recanalization had significantly better neurological outcomes (mRS ≤2) at 90 days compared to those without recanalization (46% vs. 10%, respectively; P<0.0001).
- Mortality at 90 days was significantly lower in the recanalized group compared to the non-recanalized group (32% vs. 54%, respectively; P=0.01).
- Clinically significant procedural complications occurred in 7.1% of patients, and symptomatic intracranial hemorrhage occurred in 7.8%.
Design
Study Type: Prospective, single-arm, multicenter trial (conducted in 2 parts)
Randomization:
Blinding: Single-arm, open-label. Angiographic TIMI outcomes were scored by unblinded site investigators. All 24-hour CT scans were reviewed in a core laboratory and hemorrhages were adjudicated by an independent data safety monitoring board.
Enrollment Period: May 2001 to December 2003
Follow-up Duration: Part I: 30 days (NIHSS and mRS at baseline and 30 days). Part II: additional NIHSS and mRS assessments up to 90 days.
Centers: 25
Countries: United States
Sample Size: 151
Analysis: The primary outcome was analyzed on an intention-to-treat basis. Secondary outcomes were analyzed based on the cohort in whom the device was deployed (n=141), using Fisher exact test and logistic regression.
Inclusion Criteria
- Age 18 years or older
- Signs and symptoms of acute stroke with NIHSS score ≥8
- CT scan of the brain excluding hemorrhage
- Stroke symptom duration between 3 and 8 hours, or between 0 and 3 hours with a contraindication for intravenous tPA
- Angiographically confirmed occlusion of a treatable large vessel: intracranial vertebral artery, basilar artery, intracranial carotid artery (ICA), ICA terminal bifurcation, or MCA M1 segment. Part II additionally allowed MCA M2 occlusions.
Exclusion Criteria
- Inability to obtain informed consent (waiver of consent invoked at 2 sites when no surrogate was available)
- Current pregnancy
- Serum glucose <50 mg/dL
- Excessive tortuosity of cervical vessels precluding device delivery
- Known hemorrhagic diathesis or coagulation factor deficiency
- Oral anticoagulation with INR >1.7 in Part I (>3.0 in Part II)
- Use of heparin within 48 hours, or PTT >2-times normal
- Platelet count <50,000/μL in Part I (<30,000/μL in Part II)
- History of severe allergy to contrast media
- Sustained systolic BP >185 mm Hg or diastolic BP >110 mm Hg despite treatment
- CT with significant mass effect/midline shift or hypodensity involving >1/3 of the MCA territory
- >50% stenosis of the artery proximal to the target vessel
- Life expectancy <3 months
Arms
| Field | Mechanical Embolectomy |
|---|---|
| Intervention | Attempted mechanical embolectomy using the Merci Retriever device to restore flow in an occluded intracranial large vessel. Up to 6 passes with the device were allowed. Intra-arterial thrombolytics were permitted for treatment failure or for distal emboli not accessible to the device. |
| Duration | Single procedure |
Outcomes
| Outcome | Type | Control | Intervention | HR / OR / RR | P-value |
|---|---|---|---|---|---|
| Rate of successful vascular recanalization, defined as achieving TIMI grade II or III flow in all treatable vessels immediately after treatment with the device. | Primary | 18% (Historical Control from PROACT-II) | 46% (69/151) ITT; 48% (68/141) in device-deployed cohort | <0.0001 | |
| Favorable outcome (mRS ≤2) at 30 days | Secondary | 9.9% (Not Recanalized) | 36.4% (Recanalized) | RR 3.69 (95% CI, 1.70-7.98) | 0.0002 |
| NIHSS improvement ≥10 points at 30 days | Secondary | 15.9% (Not Recanalized) | 54.0% (Recanalized) | RR 3.39 (95% CI, 1.88-6.09) | <0.0001 |
| Favorable outcome (mRS ≤2) at 90 days | Secondary | 10.4% (Not Recanalized) | 46.0% (Recanalized) | RR 4.41 (95% CI, 2.08-9.33) | <0.0001 |
| NIHSS improvement ≥10 points at 90 days | Secondary | 17.5% (Not Recanalized) | 50.0% (Recanalized) | RR 2.85 (95% CI, 1.52-5.35) | 0.0007 |
| Mortality at 30 days | Secondary | 49.3% (Not Recanalized) | 23.9% (Recanalized) | RR 0.48 (95% CI, 0.30-0.79) | 0.0028 |
| Mortality at 90 days | Secondary | 54.2% (Not Recanalized) | 31.8% (Recanalized) | RR 0.59 (95% CI, 0.39-0.89) | 0.0101 |
| Death, MI, or new stroke within 30 days | Secondary | 49.3% (Not Recanalized) | 29.9% (Recanalized) | RR 0.61 (95% CI, 0.39-0.93) | 0.0247 |
| All procedural complications | Adverse | 13% (18/141), 95% CI 7.3-18 | |||
| Clinically significant procedural complications | Adverse | 7.1% (10/141), 95% CI 2.9-11 | |||
| Symptomatic intracranial hemorrhage | Adverse | 7.8% (11/141); 5 SAH and 6 intraparenchymal (2 PH type 2) | |||
| Asymptomatic hemorrhage | Adverse | 27.7% (39/141); none SAH or PH type 2 | |||
| Embolization to previously uninvolved territory | Adverse | 3 patients (all ACA after MCA embolectomy); 1 clinically significant | |||
| Vascular dissection | Adverse | 4 patients (no immediate clinical consequence; 1 later died from GI hemorrhage on warfarin) | |||
| Intracranial vascular perforation | Adverse | 6 patients (2 with SAH); 3 clinically significant | |||
| Clinically significant groin hemorrhage | Adverse | 3 patients (requiring surgical repair or transfusion) | |||
| Device Fracture | Adverse | 11 fractures among 341 devices used; contributed to death in 2 patients |
Subgroup Analysis
Multivariate analysis identified revascularization, younger age, lower baseline NIHSS score, shorter procedure time, and left brain infarct as independent predictors of good neurological outcome. No variables predicted successful revascularization.
Criticisms
- The study was a single-arm trial that relied on a historical control for its primary efficacy endpoint, which is a major limitation compared to a randomized controlled trial.
- Angiographic assessment of recanalization (TIMI score) was performed by unblinded site investigators rather than a blinded central core lab, which could introduce bias.
- The study did not report on distal reperfusion or distal emboli, focusing only on the recanalization of the primary occlusion.
- The overall mortality rate was high (44%), which, while likely reflecting the severity of the enrolled patient population (median NIHSS 19), cannot be definitively judged as safe without a concurrent control group.
Funding
Concentric Medical Inc.
Based on: MERCI (Stroke, 2005)
Authors: Wade S. Smith, MD, PhD; Gene Sung, ..., MD; for the MERCI Trial Investigators
Citation: Stroke. 2005;36:1432-1440.
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