How did we get where we are as regards left atrial appendage occlusion (LAAO) and antithrombotics? The study by Shah and colleagues helps us chart the route [1].

The original ground-breaking trial published in 2009 randomised patients to receive LAAO or warfarin. LAAO patients were required to take warfarin for 45 days after left atrial appendage occlusion (LAAO) [2]. But in the end LAAO was approved by the FDA for patients who could take warfarin for a short duration only, despite the evidence having been accumulated in patients who could take an oral anticoagulant (OAC) long-term; just one of the idiosyncrasies of evidence-based medicine in practice!

Patients who could not take OAC were a group who might intuitively be expected to benefit from LAAO (despite the lack of evidence) and for these patients, having to take OAC for 45 days post-procedure was associated with quite a significant bleeding risk, and was a definite deterrent, for both patient and physician. As a result, doctors began to use dual antiplatelet therapy (DAPT) instead of OAC for six months after LAAO, using experience drawn from the coronary and septal closure arenas [3]. They assumed that DAPT would help prevent device thrombus formation and reduce overall bleeding risk. But really this was just conjecture and no trial firmly clarified that this was indeed the case. In fact, given that most patients presenting for LAAO are at high bleeding risk, dual antiplatelet therapy was associated with a 5–10 % chance of major bleeding in the first six months [[3], [4], [5]]. As a result, operators tried to refine device placement characteristics such that use of a single antiplatelet agent would be enough to prevent device-related thrombus while also limiting bleeding risk [6]. This is likely to be particularly relevant for the Amplatzer Amulet device, the lid of which presents a flat surface to the left atrium, effectively excluding the left atrial appendage from the circulation.