PREVAIL was conducted to assess a patient population with a higher stroke risk than the PROTECT AF patients as well as to assess for peri-procedure safety events (principally pericardial effusion) associated with Watchman implantation, which were observed in PROTECT AF. PREVAIL was a multicenter, 2:1-randomized controlled trial that enrolled 282 patients with non-valvular atrial fibrillation and a CHADS2 score ≥2. Subjects were randomized to treatment with the Watchman device (Boston Scientific, Marlborough, MA) or continued warfarin.
Patients treated with Watchman also received aspirin and warfarin until 45 days post-implant followed by aspirin and clopidogrel until 6 months post-implant. At 18 months, Watchman did not meet a pre-specified non-inferiority endpoint for stroke, systemic embolism, and cardiovascular death. This was attributed to a very low event rate in the warfarin group. The rate of pericardial effusion requiring intervention was much lower than in PROTECT AF.