“…It has been reported that in patients with incomplete surgical ligation, 50% had spontaneous echo smoke or thrombus in the LAA, whereas 22% developed thromboembolic events 12,13 . In fact, thrombus formation after implantation has been associated with both PLAATO (ev3 Inc., Plymouth, MN, USA) and AMPLATZER (AGA Medical Corp., Minneapolis, MN, USA) device, 11,14 another 2 transcatheter LAA closure systems in addition to the WATCHMAN device. Theoretically a small communication between the LA and the LAA may (1) result in higher blood velocity at the LAA os, which might actually increase the risk of stroke 15 ; and (2) produce stagnation of low velocity blood flow within the LAA that would then be a milieu of thrombus formation and continue to serve as a potential source of embolization because a port of entry into the systemic circulation still exists 11 .…”