Endovascular thrombectomy for mild strokes: How low should we go?

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Amrou Sarraj shares his research on the use of thrombectomy for mild strokes and thrombectomy as an appropriate treatment.

Recent trials have established that endovascular thrombectomy (EVT) is the standard of care for patients with acute ischaemic stroke (AIS) with large vessel occlusion (LVO) in the anterior circulation. However, these trials only included patients with a National Institute of Health (NIH) Stroke Scale (NIHSS) score of 6 and more. There are many AIS patients with LVO presenting with NIHSS<6 who can end up with disabling strokes. Physicians face uncertainty on how best to manage these patients, since milder deficits may not justify EVT risk-benefit ratio. While these patients are perceived to have good outcomes irrespective of intervention, many may worsen leading to poor outcomes. Furthermore, the belief that patients with mild strokes should be protected from the complications of invasive procedures dissuades clinicians from pursuing aggressive interventions such as EVT. Therefore, we conducted a study to shed light on the ef fectiveness and safety of EVT in this important subpopulation and to provide evidence for treating physicians in a lar ge scale, multicentre dataset that reflects worldwide daily practice.

We [Sarraj and colleagues] conducted a retrospective cohort from eight US and Spainish centres of AIS, enrolling patients with anterior circulation LVO with NIHSS≤6 presenting within 24 hours from January 2012 to March 2017. Patients were divided into two groups: EVT or medical management (MM). The primary outcome was excellent 90–day modified Rankin Scale (mRS) defined as scores 0–1. The secondary outcome was good 90 day mRS defined as scores 0–2.

This study included 277 patients, 170 received thrombectomy and 107 were treated with medical management only. Our results showed while there was no benefit in very mild strokes (NIHSS 0–3), there was a statistically significant signal towards benefit starting at NIHSS 4. Patients with NIHSS 4–5 treated with EVT had higher mRS 0–1, compared with the MM group (56.5% EVT vs. 22.2% MM) (aOR 3.90, 95%, CI 1.98–7.70, p<0.001). Similar results were seen for mRS=0–2. Our results also showed a higher incidence of symptomatic haemorrhage (sICH) in this group of patients, though it was within previously reported sICH rates (5.4% EVT vs. 0% MM; p=0.01). Mortality rates were also higher with EVT but without statistical significance in patients with NIHSS 4–5.

This study provides evidence that the arbitrary cut offs of NIHSS should not 100% dictate patients’ treatment. Some patients may benefit from further intervention, especially those with NIHSS scores of 4 and 5. Patients with eloquent areas and disabling strokes should be considered for thrombectomy, especially if advanced imaging showed potential extension of their infarct, should they not be treated. It is advised that treating physicians use the evidence and personalise treatment for the patients they are examining.

The finding that MM patients with very mild stroke (NIHSS 0–3) had better 90 – day mRS outcome came as a surprise as we were used to thrombectomy being a very effective procedure in multiple clinical trials. However, this should serve as a reminder that the benefits of thrombectomy are mainly gained in larger strokes and there are still risks with the intervention. Therefore, when approaching these patients, weighing the associated risks and benefits is crucial.

The strength of our data is that they are derived from real-world daily practice from large centers across the USA and Spain, along with the large sample and a concurrent MM comparison group. While a randomised trial would provide the highest level of evidence, it is unlikely that one will be completed for this population in the near future given the significant feasibility challenges. A randomised control trial in this population would be difficult to power: since including all patients with low NIHSS 0–5 would result in no treatment effect. It would be difficult to enroll: a limited number of patients would meet the eligibility criteria if it was restricted to NIHSS of 4–5 and difficult to execute: given the difficulty differentiating patients with one or two points differences in NIHSS.

In summary:

Patients with large vessel occlusion and mild but disabling deficits present a challenge to the treating physicians given the risk-benefit tradeoffs when considering endovascular thrombectomy.

This subpopulation was not represented in the recent trials assessing the safety and efficacy of thrombectomy thus the evidence on how to manage them remains very limited resulting in an arbitrary cutoff of NIHSS 6 as a thrombectomy criteria.

This is a large scale real world cohort from the USA and Spain that evaluated the potential treatment effect and risks associated with thrombectomy in patients with large vessel occlusion and NIHSS<6.

There was no benefit when examining the whole cohort of NIHSS 0–5. But with a deeper look into different NIHSS cutoffs there were some more findings that may shed light on how to manage this group.

In patients with NIHSS 0–3, medical management patients had better functional outcomes and safety profiles.

There was a signal towards a potential treatment effect in patients with NIHSS of 4–5.

Treating physicians should utilise this evidence when assessing their patients. While patients with lower NIHSS scales, namely 0–3, should be approached with caution, those with higher scales of NIHSS 4–5 should be considered for the procedure when deemed appropriate by the treating physicians.

The arbitrary NIHSS cutoff for thrombectomy indication at 6 is worth reconsidering.

Amrou Sarraj is associate professor in the Department of Neurology and director of the Vascular Neurology Fellowship Program at The University of Texas Health Center, USA

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