PREVAIL Study of Boston Scientific's Watchman Published

July 8, 2014—In the Journal of the American College of Cardiology, David R. Holmes, MD, et al published the findings from the PREVAIL trial, a prospective, randomized evaluation of the Watchman left atrial appendage closure device (Boston Scientific Corporation) in patients with atrial fibrillation versus long-term warfarin therapy (2014;64:1–16).

The investigators noted that the background of the PREVAIL study is the findings of the PROTECT AF trial, which studied the Watchman left atrial appendage closure technology for embolic protection in patients with atrial fibrillation. This study evaluated patients with nonvalvular atrial fibrillation (NVAF) and found that left atrial appendage (LAA) occlusion was noninferior to warfarin for stroke prevention, but a periprocedural safety hazard was identified.

The goal of the PREVAIL study was to assess the safety and efficacy of LAA occlusion for stroke prevention in patients with NVAF compared with long-term warfarin therapy.

As summarized in JACC, this randomized trial further assessed the efficacy and safety of the Watchman device. Patients with NVAF who had a CHADS2 (congestive heart failure, hypertension, age > 75 years, diabetes mellitus, and previous stroke/transient ischemic attack) score ≥ 2 or 1 and another risk factor were eligible. Patients were randomly assigned (in a 2:1 ratio) to undergo LAA occlusion and subsequent discontinuation of warfarin (intervention group; n = 269) or receive chronic warfarin therapy (control group; n = 138). The investigators assessed one safety and two efficacy coprimary endpoints.

The PREVAIL investigators reported that at 18 months, the rate of the first coprimary efficacy endpoint (composite of stroke, systemic embolism [SE], and cardiovascular/unexplained death) was 0.064 in the device group versus 0.063 in the control group (rate ratio, 1.07 [95% credible interval (CrI), 0.57 to 1.89]) and did not achieve the prespecified criteria for noninferiority (upper boundary of 95% CrI ≥ 1.75). The rate for the second coprimary efficacy endpoint (stroke or SE > 7 days postrandomization) was 0.0253 versus 0.02 (risk difference, 0.0053 [95% CrI, –0.019 to 0.0273]), achieving noninferiority.

Early safety events occurred in 2.2% of the Watchman arm, significantly lower than in PROTECT AF, satisfying the prespecified safety performance goal. Using a broader, more inclusive definition of adverse effects, these still were lower in PREVAIL than in PROTECT AF (4.2% vs 8.7%; P = .004). Pericardial effusions requiring surgical repair decreased from 1.6% to 0.4% (P = .027), and those requiring pericardiocentesis decreased from 2.9% to 1.5% (P = .36), although the number of events was small, advised the investigators.

The investigators concluded that in the PREVAIL trial, LAA occlusion was noninferior to warfarin for ischemic stroke prevention or SE > 7 days postprocedure. Although noninferiority was not achieved for overall efficacy, event rates were low and numerically comparable in both arms. Procedural safety has significantly improved. This trial provides additional data that LAA occlusion is a reasonable alternative to warfarin therapy for stroke prevention in patients with NVAF who do not have an absolute contraindication to short-term warfarin therapy, stated the investigators in JACC.