In this service review of over 500 patients treated with mechanical thrombectomy we have demonstrated that a 24/7 mechanical thrombectomy service can be delivered safely and effectively in this comprehensive stroke centre in a UK NHS hospital, with no significant difference in short- or long-term outcomes for patients admitted in-hours versus out-of-hours. This includes rates of functional independence and death at 90 days, early post-procedural complications, and symptomatic intracerebral haemorrhage. However, patients admitted out-of-hours had significantly longer door-to-groin times, with delays at all points of the treatment pathway contributing to this effect. Procedure times were, however, shorter for out-of-hours patients.
A previous service review conducted at RSUH of 106 stroke patients treated between 2009 and 2013 demonstrated that endovascular therapy could be delivered safely and effectively within this UK setting . Since this was published many changes have occurred in mechanical thrombectomy, with the publication of the landmark positive randomized controlled trials in 2015  and the use of CT perfusion software in assessing the extent of the viable penumbra in late presenters [3, 4]. This has greatly expanded the demand for mechanical thrombectomy at our unit, with 86 mechanical thrombectomies performed in 2018 compared to 18 in 2010.
In trials establishing mechanical thrombectomy as a viable treatment for acute ischaemic stroke, there was little impact on rate of death in comparison to best medical therapy . Our study reported an overall mortality of 19% at 90 days, which is higher than the 15% reported in our previous service review , with similar rates of functional independence at 90 days: 48% then versus 47% now. The difference in mortality is likely due to changes in patient selection (mean age 64 years then and 66.8 years now), with increasing age being significantly associated with mortality at 90 days in our multiple logistic regression analysis.
There are no published national data for 90-day outcomes after thrombectomy, making it difficult to gauge how our hospital’s performance compares with others in the UK. A recent service review from the Walton Centre in Liverpool showed a 33% mortality after thrombectomy; however, this review only analysed 48 patients in total . Data from the mechanical thrombectomy service at the Royal Victoria Hospital Belfast showed an overall mortality rate of 22%, of 214 patients treated between 2014 and 2017 . A meta-analysis of 8 thrombectomy RCTs in 2015 showed a mortality of 16% , and in the more recent 5 large RCTs using modern devices mortality ranged from 9 to 21% . Mortality in the 33 patients in the thrombectomy group in the UK PISTE RCT was 21%. Only 147 patients treated at our centre over the 10-year time period would be eligible for thrombectomy under SWIFT PRIME criteria. Those who did undergo thrombectomy had a similar mortality rate to those in the original trial (11% vs 9%) . Because of these more stringent inclusion criteria, mortality in RCTs tends to be lower than in unselected clinical cases.
A recent whole-country review of thrombectomy services in Germany between 2015 and 2018 found a mortality rate of 29% and a functional independence rate of 37% at 90 days . These findings are most likely a result of inclusion of high-risk patients – such as those with basilar artery occlusions, significant co-morbidities, or higher initial mRS scores –combined with an increase in treatment of patients with more borderline inclusion criteria.
Ischaemic stroke occurrence shows a diurnal variation, with the majority of strokes occurring in the morning between 9:00 am and noon . However, a recent study from the USA showed that the most common time for mechanical thrombectomy to be performed was in the evening between 21:00 and 22:00, with 58.7% of mechanical thrombectomies performed outside of normal working hours . This was similar to our data, where the majority of mechanical thrombectomies were performed out-of-hours. Currently in the UK, few centres offer a 24/7 service for mechanical thrombectomy, potentially excluding a large number of eligible patients who may benefit from this procedure.
Despite the possibility of treating patients up to 24 h post stroke onset with CT perfusion, the adage ‘time is brain’ still remains true. This makes minimizing door-to-groin times essential for improving long-term functional outcomes. Additionally, this metric acts as a surrogate marker of effective service delivery. In our previous service review only door-to-procedure-end time was recorded; on this composite metric we have significantly improved with a median reduction of over 60 min. Our median door-to-groin times are, at 124 min, better than the UK national average (149 min) in the 2018/19 data cut of the UK National Sentinel Stroke Audit , but considerably slower than the 64 min in a national audit of stroke care in the Netherlands . Long door-to-groin times out-of-hours have been reported at other centres. Two recent studies of in-hours and out-of-hours thrombectomy from the United States  and Germany  reported similar delays in door-to-groin times (21 min and 20 min respectively), but also found worse early  and late  outcomes in patients treated out-of-hours. In contrast, another study from Germany, with no delay in door-to-groin time out-of-hours, found no difference in early or late outcomes following mechanical thrombectomy . Outcomes were no different in- and out-of-hours in our hospital. This may be because delays in the early part of the pathway (door-to-groin) were compensated by more rapid procedure times at night.
On reviewing the exploratory analyses, differences in pathway timings were identified on comparison between day versus night; and weekend versus weekday, suggesting pathway delays were not limited to a specific time period. These pathway delays did not lead to major differences in long or short term outcomes.
This is the largest report of thrombectomy outcomes from a single centre in the UK, with a well-established service dating back to 2010 . Our database demonstrated a high rate of follow-up and differences in baseline demographic and clinical characteristics were controlled for in the statistical analysis, thereby removing potential biasing of the in-hours versus out-of-hours comparisons. Limitations are that there were changes in the thrombectomy pathway in our hospital and in eligibility criteria for thrombectomy over the time period, with the development of a hub and spoke model with more remote transfers over time, and more extensive use of advanced imaging and inclusion of patients up to 24 h after onset during the final 2 years.