Abstract IntroductionAtrial fibrillation (AF) is the most common sustained cardiac arrhythmia and is associated with serious morbidity. Public Health England (PHE) has used age/sex specific rates of AF obtained from a Swedish population register study to estimates the prevalence of AF in England at 2.4%, however they acknowledge that there may be limits to the generalisablity of the Swedish population to England. We aim to validate the use of this method in the English population by comparing age and gender specific rates of AF in an English nationally representative population sample.MethodsAn ontological approach was used to define a code list for AF. Age/sex specific rates of AF were calculated and compared to the estimates from the Swedish study. The prevalence of AF in the RCGP RSC cohort was also compared to that presented in the Quality and Outcomes Framework (QOF).ResultsThere were few significant differences in the age/sex specific prevalence of AF demonstrated in the RCGP RSC cohort by comparison to the Swedish study. The overall prevalence of AF in the RCGP RSC cohort was 2.73% (2.70-2.76), which was slightly lower than the prevalence (3.00%) demonstrated in the Swedish study, p=<0.001, and was higher in men, 3.18% (3.14-3.22), than in women, 2.29% (2.26-2.33). We demonstrate a prevalence of AF which is significantly higher than that estimated by QOF (1.85%), p=<0.001.DiscussionOur study demonstrates that the age/sex specific prevalence of atrial fibrillation is similar to that demonstrated in the Swedish study and validates the method used by PHE to estimate prevalence. Furthermore we estimate a prevalence of AF significantly higher than that identified through QOF registers. We demonstrate the use of an ontological approach to interrogating a nationally representative population sample to accurately estimate the burden of a chronic disease. Funding No funding to declare.