External validity of randomized clinical trials in vascular surgery: systematic review of demographic factors of patients recruited to randomized clinical trials with comparison to the National Vascular Registry

Background: Evidence-based medicine relies on randomized clinical trials, which should represent the patients encountered in clinical practice. Characteristics of patients recruited to randomized clinical trials involving vascular index operations (carotid endarterectomy, abdominal aortic aneurysm repair, infrainguinal bypass and major lower limb amputations) were compared with those recorded in the National Vascular Registry across England and Wales. Methods: MEDLINE, Embase, Web of Science, CENTRAL, clinicaltrials.gov and World Health Organization International Trials Registry Platform (CRD42021247905) were searched for randomized clinical trials involving the index operations. Demographic (age, sex, ethnicity) and clinical (co-morbidities, medications, body mass index, smoking, alcohol, cognition) data were extracted, by operation. Characteristics of operated on patients were extracted from publicly available National Vascular Registry reports (2014–2020). All findings are reported according to PRISMA guidelines. Rayyan.AI, Excel and GraphPad Prism were used for screening and analysis. Results: A total of 307 randomized clinical trials (66 449 patients) were included and compared with National Vascular Registry data for 119 019 patients. Randomized clinical trial patients were younger across all operations; for carotid endarterectomy, bypass and major lower limb amputation randomized clinical trials, there were differences in female patient representation. Further comparisons were limited by the insufficient baseline data reporting across randomized clinical trials, though reporting improved over decades. National Vascular Registry reports lacked information on patient factors such as patient ethnicity or body mass index. Conclusions: There are significant differences in demographic and clinical factors between patients recruited to vascular surgery randomized clinical trials and the real-world National Vascular Registry vascular surgery patient population. Minimum reporting standards for baseline data should be defined to allow future randomized clinical trials to represent real-world patient populations and ensure the external validity of their results.