Boston Scientific Corporation (NYSE:BSX) issued a press release on November 2, 2026, announcing positive six-month primary endpoint results from the SIMPLAAFY randomized controlled trial of the WATCHMAN FLX Pro Left Atrial Appendage Closure Device.

Key Highlights

  • Trial size: The SIMPLAAFY trial randomized 1,857 patients across 86 clinical study sites in the U.S.
  • Non-inferiority achieved: Both aspirin alone and reduced-dose NOAC alone regimens each achieved noninferiority to dual anti-platelet therapy (DAPT) at six months.
  • Equivalent ischemic stroke rates: Patients on the single-drug regimens experienced equivalent ischemic stroke rates to DAPT, reported at 0.7%.
  • Device-related thrombus rate: At 45 days, device-related thrombus was lowest in the reduced-dose NOAC group compared to DAPT (0.9% vs. 3.4%; P=0.01).
  • Publication: Results were presented at TCT 2026 and simultaneously published in JAMA.
  • Investigational status: Aspirin alone or reduced-dose NOAC alone following implantation with the WATCHMAN FLX Pro device is described as an investigational post-implant drug regimen.

SIMPLAAFY Six-Month Results: Single-Drug Regimens and WATCHMAN FLX Pro

According to the filing, the SIMPLAAFY trial assessed whether two single-drug post-implant regimens could serve as alternatives to DAPT following implantation of the WATCHMAN FLX Pro Left Atrial Appendage Closure Device in patients with non-valvular atrial fibrillation (NVAF). The trial compared an aspirin-alone regimen, a reduced-dose non-vitamin K antagonist oral anticoagulant (NOAC) for the first three months followed by aspirin only, and a DAPT regimen of aspirin and clopidogrel for the first six months followed by aspirin only. The study will follow patients through 12 months, the company disclosed.

At the six-month mark, the filing states that both single-drug regimens achieved noninferiority to DAPT, with patients on those regimens experiencing less bleeding and equivalent ischemic stroke rates of 0.7%. At the 45-day imaging assessment, the rate of device-related thrombus was reported as lowest in the reduced-dose NOAC group at 0.9%, compared to 3.4% in the DAPT group (P=0.01), according to the filing. The WATCHMAN FLX Pro device includes HEMOCOAT Technology, which the company describes as "designed to enable more controlled, faster healing following implantation."

Boston Scientific noted that the WATCHMAN FLX Pro received U.S. Food and Drug Administration approval in 2023, and that the WATCHMAN implant has helped reduce stroke risk for more than 800,000 patients worldwide over more than two decades of clinical evidence, according to the filing. The company also disclosed that enrollment in the Elite AF trial, evaluating the next-generation WATCHMAN Elite LAAC Device, commenced in 2026. The filing notes that the investigational drug regimens disclosed in this trial are not currently approved post-implant protocols.

What Was Disclosed

Boston Scientific disclosed six-month primary endpoint results from the SIMPLAAFY randomized controlled trial, showing that two single-drug post-implant regimens each achieved noninferiority to DAPT in 1,857 patients implanted with the WATCHMAN FLX Pro device across 86 U.S. sites.