Left atrial appendage closure: prevalence and risk of device-associated thrombus formation

There remains no doubt that atrial fibrillation (AF) is associated with an increased stroke risk (1). It is also clear that the vast majority of thrombi in patients with non-valvar AF are located in the left atrial appendage (LAA) (2). Multiple randomized trials have demonstrated a mortality and stroke rate reduction with anticoagulation using a vitamin K antagonist (3). More recently, the superiority of LAA closure using a nitinol cage (Watchman device) over anticoagulation with a vitamin K antagonist has been shown regarding all-cause mortality (driven by a lower rate of intracranial hemorrhage), disabling strokes and long-term bleeding (disregarding the up-front rate of pericardial bleeding) (4). Therefore, in most countries, LAA closure has established itself as the treatment of choice in patients with a high or prohibitive bleeding risk, despite the fact that its utility has been shown in a different patient population, those with a low bleeding risk who are able to tolerate anticoagulation. Optimally, a LAA closure device would seal the LAA completely leaving no potentially thrombogenic LAA tissue behind and not cause thrombus formation both of which may diminish and, perhaps, off-set the (stroke prevention) benefits of the procedure. The reality is that neither applies to the current technology. In fact, regardless of the device or trial, device-associated thrombus formation (DTF) has been reported. It has been less clear if and to what degree the discovery of this finding increases the stroke risk. Previously, based on the observed device-associated thrombus rate of 20/478 patients (4.2%) in PROTECT-AF of whom 3 had a stroke prior to detection, the device-thrombus associated stroke risk has been estimated to be 0.3% per 100 patient years. In other words, it has been assumed that the risk of stroke caused by DTF per year is only 0.3% (5). From a different perspective, however, one could assume that the risk of a stroke in the presence of DTF is at least 3/20 (=15%) not taking into account that some of the other reported strokes at follow-up may have been related to unknown DTF (or thrombi no longer seen on the device as they have embolized). Hence, the DTF rate has not received as much attention as it, perhaps, should. Therefore, the findings of the recently published manuscript by Fauchier et al. in the Journal of the American College of Cardiology are very important (6). Data from 469 consecutive patients who underwent LAA closure, in the overwhelming majority with the Watchman device, Amplatzer Cardiac Plug or Amulet, were retrospectively