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Research and Projects

PenCHORD - Maximising access to thrombectomy services for stroke in England

Who is involved?

Theme: PenCHORD
Status: Complete


Endovascular thrombectomy is a ground-breaking new treatment for severe stroke which requires specialist expertise and equipment. PenCHORD have collaborated with the Stroke Association, the National Institute for Health Research (NIHR) and NHS England in order to identify where and how this new service could be provided to maximise access to patients, and how it should interact with existing acute stroke services.

Results showed that it is not possible for all current acute stroke units to provide and sustain the number of thrombectomy procedures required (at least 150 per year) to maintain an expert service. The maximum number of centres providing thrombectomy would be 40. It is therefore likely that a significant proportion of patients would require transfer from a local acute stroke unit to a comprehensive stroke unit providing thrombectomy, if they were judged suitable.

Modelling indicated that if ambulance crews started transferring patients directly to comprehensive stroke centres, local acute stroke services may be destabilised and comprehensive stroke centres may become overwhelmed. It was concluded that clear rules for ambulance crews will be required for effective roll-out of thrombectomy services.


The project aimed to determine:

  • How many stroke units could provide a sustainable thrombectomy service, assuming that at least 150 procedures per year need to be carried out

  • Where should these centres be located?

  • Should patients be transferred directly to a comprehensive stroke centre providing thrombectomy if there was minimal effect on travel time (e.g. no more than 15 minutes extra travel time)?

Project activity

Modelling was based on the home location of 238,887 acute stroke patients admitted to hospital in England between 2013 and 2015. A bespoke ‘genetic algorithm’ was used to explore and optimise the number and choice of location of units potentially providing thrombectomy. 

Feasibility of a mothership model where all patients attend their closest comprehensive stroke centre providing thrombectomy.

The panels show the relationship between the number of centres and best identified results for:

  • (left panel) average and maximum travel time to centre

  • (centre panel) greatest and fewest admissions per year to any single centre

  • (right panel) the proportion of patients attending a centre within 45 minutes and providing at least 150 ET procedures per year


Modelling results have been provided to the Stroke Association (who jointly funded the project with PenCLAHRC), NHS England, and the NIHR's Promoting Effective and Rapid Stroke Care (PEARS) Project (which is looking at how best to implement thrombectomy services). This is now informing the review of roll-out of thrombectomy services in England.

Professor Tony Rudd, National Clinical Director for Stroke, NHS England, notes that:

‘The modelling work undertaken by PenCHORD has been invaluable in helping the NHS decide how and where services for thrombectomy for stroke should be organised. It has also raised critical questions about the organisation of the whole of acute stroke care in way that will influence the new National Stroke Plan for England'  


Allen M, Pearn K, James M, Ford GA, White P, Rudd AG, McMeekin P, Stein K. Maximising access to thrombectomy services for stroke in England: A modelling study. European Stroke Journal 2018; DOI: 10.1177/2396987318785421

Allen M, Pearn K, Monks T, Bray BD, Everson R, Salmon A, James M, Stein K. Can clinical audits be enhanced by pathway simulation and machine learning? An example from the acute stroke pathway BMJ Open 2019;9:e028296.


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Next Steps

PenCHORD are working with NHS England to define the next steps, likely to be more regional analysis of provision of thrombectomy services.