Mechanical thrombectomy devices for acute ischaemic stroke

Level of innovation

The specialists thought that the devices were highly innovative and a novel concept, with 1 describing the technologies as a 'paradigm shift' in the treatment of acute ischaemic stroke. Two others highlighted that mechanical thrombectomy (MT) was partly a redevelopment of existing technologies used in neuro-intervention, but acknowledged that the concept was highly novel.

One specialist stated that the technique is arguably now the standard care for intracranial large-vessel occlusion; however, another suggested that uptake of MT techniques in the UK had been slow, and that the devices were still relatively new in this setting. One specialist commentator disagreed with this statement, and said that although the numbers of procedures are low compared with international standards (because of delays in commissioning of services), there has been a higher level of uptake of these techniques in centres with the right resources.

One specialist noted that stent retriever type devices are used most commonly in the UK, while a further 2 specialists highlighted that the current evidence base favours stent retrievers.

Potential patient impact

The specialists remarked that using the technology could lead to substantial patient benefits, particularly in post-stroke morbidity and disability. Improvements in functional outcomes, including functional independence; short- and long-term disability; recovery times and length of hospital stay; complications; and carer burden were all cited as potential benefits of MT. One specialist added that the likelihood of functional recovery for patients having the treatment was 50% to 70%, compared with about 10% for conventional medical treatment. Another specialist noted this level of functional recovery will only happen when an excellent technical thrombectomy result is achieved within 4.5 hours of the stroke onset.

The specialists stated that MT devices could be particularly beneficial in: patients with confirmed large proximal acute ischaemic stroke or large-vessel occlusion (who make up around 10% of all stroke patients); patients with no significant established infarct; people presenting 4 to 6 hours after the onset of symptoms; patients on warfarin or a direct-acting oral anticoagulant; patients who cannot have intravenous thrombolysis; patients who have already had intravenous thrombolysis; and those presenting past 4.5 hours, with or without perfusion scanning.

The figure of about 10% of stroke patients having large-vessel occlusion was disputed by 1 specialist who suggested the figure, based on prospective studies and RCTs, was between 39 and 56% of acute ischaemic stroke. The specialist suggested that 10% represents those patients with large-vessel occlusions presenting in time for MT with no additional contraindications.

Potential system impact

Specialists proposed that the devices could have a positive effect on NHS and social services by reducing length of hospital stay and longer-term care costs post-stroke. One specialist remarked that it is anticipated that care for stroke patients treated with MT would move from a long inpatient stay to a short stay with subsequent outpatient follow-up.

The specialists commented that there would be a large upfront cost to the healthcare system associated with uptake of the devices. But they felt that this would be off-set by long-term savings because of the reduced long-term care burden for patients with stroke, as shown in published cost-effectiveness studies. The costs of purchasing the devices, training large numbers of interventional neuroradiologists and other clinical and support staff, and providing additional staffing and facilities for 24-hour services were all cited as sources of additional costs to the NHS.

Several specialists thought that more widespread use of MT devices would need substantial changes to facilities and infrastructure. One suggested that stroke services would need to be centralised into fewer larger units that can deliver MT. The specialist thought that this could lead to destabilisation of smaller stroke units and those that were unable to provide thrombectomy. Specialists also suggested that the effect on ambulance services would be significant because more inter-hospital transfers would be needed. One noted that transport may be a problem in areas that are far from existing neuroscience centres, but noted that 85% of the population is within 1 hour of a centre. Two specialists noted that access to neuro-optimised angiographic facilities would be needed to offer a complete thrombectomy service, and 1 added that a back-up angiography machine on site would also be needed. One commentator noted that having a back-up angiography machine is in line with NHS England service specifications.

Specialists identified problems with staffing (providing and training staff to offer 24-hour thrombectomy services) as the most likely problem that could prevent the technology from being adopted in the NHS. For instance, 2 specialists referred to the British Society of Neuroradiologists' training guidance for mechanical thrombectomy, which noted that the numbers of fully trained interventional neuroradiologists in the UK would have to double to meet the demands of a 24/7 MT service. One specialist noted that to provide efficient care in hyperacute stroke units and comprehensive stroke centres care, further centralisation of stroke services would be needed. One specialist commented (and another agreed) that imaging protocols at hyperacute stroke units would also need to be upgraded to enable rapid access to CT or magnetic resonance (MR) angiography. If this didn't happen, the thrombectomy pathway would not be activated early enough for clinical benefit to be realised in many patients.

General comments

A number of specialists emphasised that MT is a complex and technical intervention. Because of this it is important that clinicians doing the procedure are highly trained to avoid substantial patient morbidity and mortality. One specialist added that training plans would need to ensure that clinicians were sufficiently skilled to achieve the same efficacy and safety profile when delivering the procedure in practice as had been seen in clinical trials. Without this measure, the benefits of MT would likely to be lost. Another stated that adopting the procedure in non-neuroscience centres, without ensuring that operators had the right credentials and adequate training, would likely to be unsafe. One specialist also stated the procedure should be completed as early as possible to improve outcomes.

Specialists also remarked that only 1 or 2 stroke centres in the UK currently operate 24 hours a day, 7 days a week. They thought that 24‑hour services would be needed at all centres in order to deliver a complete thrombectomy service. Specialists stated that the devices are currently used in the NHS in commissioned neuroscience centres and that about 500 procedures are performed annually. This need is expected to increase in future years, with current forecasts suggesting that up to 8,000 patients per year could be eligible for the procedure. One specialist suggested that, once 24‑hour services are provided across England, a large thrombectomy centre would expect to perform about 5 or 6 MT procedures per week.

A number of specialists thought that further research was needed in the field of MT with the following topics highlighted: head-to-head comparisons of stent retriever and aspiration type devices; the benefits of using MT for more distal occlusions (such as M2 segment occlusions); the relative risks of using general anaesthesia or conscious sedation for the procedure; comparing MT alone against MT with tissue plasminogen activator; and comparing direct transfer of patients to thrombectomy centres compared with a model in which patients are transferred from local hyperacute stroke units.