BACKGROUND: Heart failure (HF) is a risk factor for stroke among people with atrial fibrillation (AF). Prognosis following an HF diagnosis is often poor, but this is not accounted for in existing stroke risk scores. AIM: To examine stroke incidence in people with HF and AF compared with AF alone, considering the competing risk of death. DESIGN AND SETTING: A population-based retrospective cohort study in English primary care, linked to secondary care Hospital Episode Statistics data. METHOD: In total, 2 381 941 people aged ≥45 years were identified in the Clinical Practice Research Datalink from 2000 to 2018. HF and AF were included as time-varying covariates
69 575 had HF and AF, 141 562 had AF alone, and 91 852 had HF alone. Hazard ratios (HRs) for first stroke are reported using the Cox model and the Fine-Gray model. RESULTS: Over median follow-up of 6.62 years, 93 665 people (3.9%) had a first stroke and 314 042 (13.2%) died. Over half (51.3%) of those with HF, with or without AF, died. In the fully adjusted Cox model, relative stroke risk was highest among people with AF alone (HR 2.43, 95% confidence interval [CI] = 2.38 to 2.48), followed by HF and AF (HR 2.20, 95% CI = 2.14 to 2.26). The cumulative incidence function of stroke was also highest among those with AF only once accounting for the competing risk of all-cause mortality. In a Fine-Gray model, the relative risk of stroke was similar for people with AF alone (HR 2.38, 95% CI = 2.33 to 2.43), but there was significant attenuation among those with HF and AF (HR 1.48, 95% CI = 1.44 to 1.53). CONCLUSION: HF is an aetiological risk factor for stroke, yet its prognostic significance is reduced by the high incidence of death. Use of the CHA