External Validity of Randomised Controlled Trials on Carotid Revascularisation: Trial Populations May Not Always Reflect Patients in Clinical Practice

Abstract

The external validity of randomised controlled trials (RCTs) and their transferability to clinical practice is under investigated. This study aimed to analyse the exclusion criteria of recent carotid RCTs comparing carotid endarterectomy (CEA) and carotid artery stenting, and to assess the eligibility of consecutive clinical practice cohorts to those RCTs. An analysis of the clinical and anatomical exclusion criteria of RCTs for asymptomatic (SPACE-2, ACST-2, CREST-1, and CREST-2) and symptomatic carotid stenosis (SPACE-1, CREST-1, ICSS, and EVA-3S) was performed. Two hundred consecutive asymptomatic and 200 consecutive symptomatic patients, treated by CEA, or transfemoral or transcarotid artery stenting at a tertiary referral university centre were assessed for their potential eligibility for each corresponding RCT. RCT patient data were pooled and differences from the clinical practice cohort analysed. Statistics were descriptive and comparative using Fisher's exact and t tests. The number of clinical and anatomical exclusion criteria differed widely between RCTs. Potential eligibility rates of the clinical practice cohort for RCTs with regard to asymptomatic carotid stenosis were 80.5% (ACST-2), 79.5% (SPACE-2), 47% (CREST-1), and 20% (CREST-2). For RCTs on symptomatic carotid stenosis the eligibility rates were 89% (ICSS), 86.5% (EVA-3S), 64% (SPACE-1), and 39% (CREST-1). Both clinical practice cohorts were older by about three years and patients were more often male vs. the RCTs. Furthermore, a history of smoking (asymptomatic patients), hypertension (symptomatic patients), and atrial fibrillation was diagnosed more often, whereas hypercholesterolaemia and coronary heart disease (asymptomatic patients) were less prevalent. More clinical practice patients were on antiplatelets, anticoagulants, and lipid lowering drugs. Symptomatic clinical practice patients presented more often with retinal ischaemia and less often with minor hemispheric strokes than patients in the RCTs. The external validity of contemporary carotid RCTs varies considerably. Patients in routine clinical practice differ from RCT populations with respect to age, comorbidities, and medication. These data are of interest for clinicians and guideline authors and may be relevant for the design of future comparative trials.