PDF: MERCI
(2005)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
• 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. Clinical follow-up was for 90 days.
Study Design
Arms: Array
Outcome
• Good neurological outcome (mRS ≤2 at 90 days) was achieved in 46% of recanalized patients vs. 10% of non-recanalized patients (p<0.0001).
• 90-day mortality was 32% in recanalized patients vs. 54% in non-recanalized patients (p=0.01).
• Symptomatic intracranial hemorrhage occurred in 7.8% of treated patients.
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%.
Study Design
- Study Type
- Prospective, single-arm, multicenter trial
- Randomization
- No
- Blinding
- This was a single-arm, open-label study. Angiographic outcomes were scored by unblinded site investigators. A data safety monitoring board adjudicated hemorrhages.
- Sample Size
- 151
- Follow-up
- 90 days
- Centers
- 25
- Countries
- United States
Primary Outcome
Definition: Rate of successful vascular recanalization, defined as achieving Thrombolysis In Myocardial Infarction (TIMI) grade II or III flow in all treatable vessels immediately after treatment with the device.
| Control | Intervention | HR/OR | P-value |
|---|---|---|---|
| 18% (Historical Control from PROACT-II) | 46% (69/151) | - | <0.0001 |
Limitations & 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.
Citation
Stroke. 2005;36:1432-1440.