In the rivaroxaban group there were 7 thromboembolic events (4 ischaemic strokes and 3 MIs) and 4 major bleeding events. In the warfarin group there were 2 major bleeding events (no thromboembolic events). The authors conclude that rivaroxaban apparently does not protect high-risk patients from arterial events; reasons for this remain elusive. Possible explanations may be related to insufficient drug concentration; animal models have suggested higher anti-Xa activity and plasma rivaroxaban levels are required for the prevention of arterial vs venous events. Differences in the mechanisms of action of rivaroxaban and warfarin may also, in part, explain the findings.
The study included only high-risk patients with triple-positive antiphospholipid syndrome (lupus anticoagulant, anticardiolipin, and beta-2-glycoprotein positive). The authors say the therapeutic strategy in patients with a laboratory profile different from that of this study should be considered on a case-by-case basis, taking into account the presence of additional risk factors for venous and arterial thrombosis, the nature of venous thromboembolism (provoked or unprovoked), and the risk for bleeding.