The PREVAIL trial compared the WATCHMAN LAA closure device to warfarin for stroke prevention in patients with atrial fibrillation. The trial randomized 407 patients across 41 US centers to receive either the device or warfarin therapy. The primary endpoints were acute safety events within 7 days, and rates of stroke, systemic embolism, and cardiovascular death out to 18 months. The goal was to confirm the safety results from prior trials and demonstrate the safety of the device when implanted by new operators.