So, DAWN and DEFUSE-3 show it is reasonable to use tissue-based criteria to guide intervention, rather than the quaint, but anachronistic, concept of “time is brain.” However, in expanding this window, what is the yield of screening? How many CT cerebral angiograms with specialized perfusion imaging will need to be performed to identify a patient for intervention?
This single-center report 2014 through 2017 at a DAWN trial-participating center found:
- 2,667 patients with acute ischemic stroke.
- 792 arrived between 6 and 24 hours of last known to be normal.
- 298 of those were NIHSS ≥10.
- 155 of those had proximal anterior large vessel occlusion.
- 45 of those were non-disabled at baseline and met clinical and imaging mismatch criteria.
The authors also did an analysis for DEFUSE-3 eligibility, and ended up with similar numbers, although there were 15 DAWN-eligible patients who did not meet DEFUSE-3 criteria and 28 DEFUSE-3 patients who did not meet DAWN criteria, so there’s some fuzziness at the bottom of the pyramid, in addition to the limitations of their retrospective review.
So, effectively, a little more than a third of patients presenting between 6 and 24 hours probably meet criteria for screening for large-vessel occlusion, with about half of those identifying an occlusion, and then another third of those having imaging findings with sufficient viable tissue for intervention.
There are almost certainly opportunities to use clinical evaluation – not just a NIHSS cut-off – to improve yield, but there will inevitably be a balance between sensitivity and specificity with respect to resource utilization.
“Eligibility for Endovascular Trial Enrollment in the 6- to 24-Hour Time Window”
http://stroke.ahajournals.org/content/early/2018/03/15/STROKEAHA.117.020273
Roughly 1-2% of all CVA patients were eligible for thrombectomy between 6-24hrs. However, not all of them will benefit from the treatment. In the DAWN trial it was 33% adjusted absolute difference. This means less than 1% of people in that window will benefit from this therapy. What will be the benefit and harm when the treatment is offered outside the very controlled environment of a research study?
That’s essentially the question to address when organizing a stroke triage system for a region – most strokes aren’t eligible, and even of those eligible, what’s the value in expending resources to activate a specialized center? Pre-hospital evaluation/telemedicine becomes much more useful.