Clinical Context

Acute ischemic stroke occurs when the blood supply to part of the brain is reduced or interrupted, resulting in the death of brain cells in that area. Treatment varies depending on time from stroke onset and indications from brain imaging, but it can include medication to dissolve the blocking blood clot, also called intravenous tissue plasminogen activator (IV t-PA). Endovascular procedures, like a thrombectomy to remove the blood clot, can also treat the blocked vessel. There are limited treatment options for acute ischemic stroke patients with wake-up or late presenting strokes.

Device Description

The Trevo Retriever family (510(k) clearance K173352), including the Trevo ProVue and Trevo XP ProVue Retriever, are Class II medical devices cleared in February 2018. They are neurovascular mechanical thrombectomy devices for acute ischemic stroke treatment that consist of a flexible, tapered core wire with a shaped section at the distal end; see Substantial Equivalence Clearance K173352 (PDF).

Indications for Use

A clinical study was used to support an expanded indication for use of the Trevo Retriever to include the following:

The Trevo Retriever is indicated for use to restore blood flow in the neurovasculature by removing thrombus for the treatment of acute ischemic stroke to reduce disability in patients with a persistent, proximal anterior circulation, large vessel occlusion of the internal carotid artery (ICA) or middle cerebral artery (MCA)-M1 segments with smaller core infarcts (0-50 cc for age < 80 years, 0-20 cc for age ≥ 80 years). Endovascular therapy with the device should start within 6-24 hours of time last seen well in patients who are ineligible for intravenous tissue plasminogen activator (IV t-PA) or who fail IV t-PA therapy.

Context of Clinical Outcome Assessment (COA) Use

In the clinical study used to support the expanded indications for use, the co-primary effectiveness endpoint included:

• A new utility weighted modified Rankin Scale (UW-mRS) 
• The more traditional dichotomous mRS (0-2 vs. 3-6) to claim study success and compare the treatment arm to the control arm of best medical therapy.

The mRS (a clinician-reported outcome, or ClinRO) reflects a clinician’s rating of a patient’s disability on a scale from 0-6. The UW-mRS (ClinRO) assigns weights to each of the 7 individual mRS scores. Study success could only be claimed if both clinical outcome assessments showed superiority of the treatment arm compared to the control arm.

Additionally, the National Institutes of Health Stroke Scale (NIHSS), another ClinRO, was used to determine a patient’s study eligibility. The incidence of neurological deterioration from baseline NIHSS score was used to inform the secondary safety endpoint.

Lessons Learned

The use of the UW-mRS along with a more traditional ClinRO like the dichotomized mRS can be used to validate this new ClinRO as it is used more in clinical studies of acute ischemic stroke therapies. One benefit of the new UW-mRS is that it incorporates what may be clinically meaningful for patients and their caregivers into a ClinRO to determine the functional disability following a stroke. As this UW-mRS is used more in clinical studies, it may provide a more meaningful assessment of the safety and benefit of new therapies from both a clinical and patient-level perspective in comparison to the more traditional dichotomized or ordinal mRS.