PDF: SWIFT PRIME
(2015)Objective
To determine whether adding stent retriever thrombectomy to IV tPA improves outcomes in anterior circulation LVO stroke within 6 hours.
Study Summary
Intervention
IV alteplase (0.9 mg/kg) with or without Solitaire stent retriever thrombectomy, initiated within 6 hours of symptom onset.
Inclusion Criteria
Age 18-80, moderate-to-severe deficits (NIHSS ≥8 and <30 at randomization), imaging-confirmed occlusion of the intracranial ICA and/or the first segment of the MCA (M1), small/moderate infarct core on qualifying imaging, receiving/received IV tPA, endovascular treatment initiable within 6 hours of last-known-well.
Study Design
Arms: IV tPA + Thrombectomy vs. IV tPA Alone
Patients per Arm: Both arms: 98
Outcome
Bottom Line
In patients receiving intravenous t-PA for acute ischemic stroke due to proximal anterior intracranial circulation occlusions, thrombectomy with a stent retriever within 6 hours after onset significantly improved functional outcomes at 90 days, without significantly increasing mortality or symptomatic intracranial hemorrhage.
Major Points
- One of five landmark 2015 thrombectomy RCTs. Unique for being the only trial to require IV tPA in both arms (bridging therapy mandatory) and the only industry-sponsored trial in the group.
- Stopped early at 196 patients (target 833) after interim analysis showed overwhelming efficacy — the largest absolute treatment effect among the 2015 trials.
- Functional independence (mRS 0–2) at 90 days: 60% thrombectomy vs 35% IV tPA alone (NNT 4, p<0.001) — the highest absolute benefit of any 2015 thrombectomy trial.
- mRS ordinal shift analysis also significant (p<0.001). 0% sICH in the thrombectomy group vs 3% in control — the only 2015 trial with lower sICH in the intervention arm.
- 88% achieved substantial reperfusion (mTICI 2b/3) — among the highest rates in the 2015 trials, reflecting experienced operators and Solitaire device efficacy.
- Imaging criteria evolved mid-trial: initially required target-mismatch perfusion profile (CT perfusion using RAPID software), later changed to small-to-moderate core strategy (ASPECTS-based). Both criteria yielded positive results.
- Occlusion sites: ICA ~17%, M1 ~72%, M2 ~10%. Solitaire FR or Solitaire 2 was the mandated first-line device.
- Workflow was fast: median qualifying image to groin puncture 57 min, ED arrival to groin puncture 90 min, onset to first stent retriever deployment 252 min.
- Successful reperfusion at 27 hours on perfusion imaging: 83% thrombectomy vs 40% control (p<0.001). NIHSS improvement at 27h: −8.5 vs −3.9 (p<0.001).
- 90-day mortality: 9% vs 12% (p=0.50) — numerically lower in thrombectomy group but not significant.
- Contributed to the 2015 AHA/ASA Class IA recommendation for thrombectomy in LVO stroke within 6 hours.
Study Design
- Study Type
- International, multicenter, prospective, randomized, open-label parallel-group trial (PROBE design) with blinded core-lab imaging and outcome assessment
- Randomization
- Yes
- Blinding
- Open-label treatment; blinded core-laboratory assessment of neurovascular imaging and independent adjudicated outcome assessment
- Sample Size
- 196
- Follow-up
- 90 days
- Centers
- 39
- Countries
- United States, Europe
Primary Outcome
Definition: Severity of global disability at 90 days, as assessed by means of the modified Rankin scale (scores 0 [no symptoms] to 6 [death]). Both overall distribution shift and proportion of patients with functional independence (mRS 0-2) were used as simultaneous success criteria.
| Control | Intervention | HR/OR | P-value |
|---|---|---|---|
| Median mRS: 3 (IQR 2-5) | Median mRS: 2 (IQR 1-4) | - (Common OR 2.63 (1.57–4.40)) | <0.001 |
Limitations & Criticisms
- Mandatory IV tPA in both arms — excludes patients ineligible for thrombolysis (late presenters, anticoagulated, recent surgery), limiting generalizability to the direct thrombectomy population.
- Stopped early at 196/833 patients (24%) — the most extreme early termination among the 2015 trials, potentially overestimating treatment effect.
- Industry-sponsored (Covidien/Medtronic) — the only 2015 thrombectomy trial with full industry sponsorship, raising potential conflict of interest concerns.
- Imaging eligibility changed mid-trial from perfusion-based target mismatch to ASPECTS-based core strategy — introduces heterogeneity in patient selection.
- All sites were tertiary centers with experienced neurointerventionalists and a continuous quality-improvement program — workflow times may not be achievable in community settings.
- Excluded M2 and posterior circulation occlusions — later addressed by trials like ASTER 2 and BASICS.
- No comparison with aspiration-first technique (ADAPT) — only Solitaire stent retriever evaluated.
- 6-hour time window — does not address late-presenting patients, who were later shown to benefit in DAWN and DEFUSE 3.
Citation
N Engl J Med 2015;372:2285-95.