Although the mechanism of thromboembolism in AF is multifactorial, the LAA appears to be the major source of thrombus and is a target for transcatheter interventional therapy with device occlusion or ligation. The WATCHMAN has the largest data set for clinical end points, having been evaluated in 2 randomized trials and an FDA-monitored continuing-access registry in warfarin-eligible patients. In total, these studies support the clinical efficacy of the WATCHMAN in preventing thromboembolic events in the absence of anticoagulation and, in turn, provide mechanistic support for the concept of LAA closure for stroke prevention in at-risk patients. However, extrapolating these findings to other LAA devices is perilous because there are limited safety data and a paucity of robust clinical outcomes data for alternative approaches to LAA closure. Patient selection for the WATCHMAN device should be guided by an assessment of thromboembolic and bleeding risk, in addition to patient preference.
The report also cites a smaller trial which failed to establish non-inferiority of the device over anticoagulation, but noted a remarkably low event rate in the anticoagulation group.