Risk of bleeding and arterial thromboembolism in patients with non-valvular atrial fibrillation either maintained on a vitamin K antagonist or switched to a non-vitamin K-antagonist oral anticoagulant: a retrospective, matched-cohort study - Bouillon, K; Bertrand, M; Maura, G; Blotière, P O; Ricordeau, P; Zureik, M (Lancet Haematol, 2015)