BackgroundRecent randomised clinical trials have suggested prognostic benefits of catheter ablation in highly selected patients with atrial fibrillation (AF) and heart failure (HF).ObjectivesThis study sought to identify the treatment effect associated with catheter ablation in a broad population of patients with AF and HF.MethodsThrough nationwide administrative registers in Denmark, we estimated the 2-year average treatment effect (ATE) of catheter ablation for AF on a composite endpoint of HF readmission, stroke and all-cause mortality at 1-year and 5-year landmark analyses. The primary cohort was patients with AF before HF, and the second cohort of patients with HF before AF.ResultsA total of 13 756 patients were included with 9904 patients in the primary cohort, and 3852 in the secondary. An ATE (95% CI) reduction of the composite endpoint of 7.0% (4.5% to 9.5%) was observed in the primary cohort and 11.8% (6.0% to 17.6%) in the secondary in the 1-year landmark analysis with a reduction in all-cause mortality of 5.8% (3.7%–7.8%) and 6.3% (0.9%–11.7%), respectively. At the 5-year landmark, catheter ablation was associated with reductions in the composite endpoint and all-cause mortality in the primary (4.7% (2.3% to 7.2%), and 3.6% (1.0% to 6.3%), respectively), but not in the secondary cohort.ConclusionsAblation was associated with decreased risk of HF readmission, stroke and all-cause mortality in patients with AF and HF. The effect is most substantial in patients with AF before HF and with catheter ablation after 1 year from the diagnosis of both conditions.