Ilyas K. Colombowala, MD, FACC, FHRS
Cardiac Electrophysiology · Houston, TX · colombowala.com
EP Staff Education Clinical Staff Ilyas Colombowala, MD, FACC, FHRS →
Patient library → ← Main site

Device

WATCHMAN FLX Overview

The Boston Scientific WATCHMAN FLX is a left atrial appendage closure device deployed via transseptal catheter under TEE guidance. Covers device design, sizing, deployment criteria, the post-implant antithrombotic bridge, and the 45-day seal confirmation.

Common issues / troubleshooting

  • ▸Peri-device leak >5 mm on 45-day TEE — delays transition off anticoagulation and may need additional closure.
  • ▸Device-related thrombus on the LA-facing surface — surveillance TEE finding; usually managed with reinstated anticoagulation.
  • ▸Pericardial effusion during deployment from over-aggressive transseptal puncture or shoulder over-extension.
  • ▸Inadequate LAA ostium sizing — under-sized device embolises, over-sized device fails to seal.
  • ▸Air embolism during sheath exchange — pay attention to deairing and sheath positioning.

The WATCHMAN FLX is a left atrial appendage closure device used to occlude the LAA in non-valvular AF patients who want to come off long-term oral anticoagulation. It mechanically excludes the appendage from the systemic circulation; once endothelialised, the device removes the dominant source of cardioembolic stroke in AF.

How the system works

  • A self-expanding nitinol frame with anchoring barbs around the shoulder, covered on the LA-facing side by a permeable PET fabric.
  • Deployed through a 14F sheath via transseptal puncture into the LAA ostium.
  • The shoulder barbs engage the LAA wall just distal to the ostium; the fabric face sits flush with the LA endocardium.
  • Over 45-90 days, endothelial tissue covers the LA face, sealing the appendage permanently.

Types / Variants

The current US platform is WATCHMAN FLX (replacing the original WATCHMAN 2.5). Available in five sizes (20, 24, 27, 31, 35 mm) covering ostia from roughly 14 to 31 mm.

The next-generation WATCHMAN FLX Pro with HDD (high-density device) and a thromboresistant fluorinated polymer coating expands the platform further on more recent rollouts.

Indications & candidate selection

Standard indication: non-valvular AF with elevated stroke risk (CHA2DS2-VASc >=2 in men, >=3 in women) and an appropriate reason to discontinue long-term anticoagulation:

  • Major bleeding on anticoagulation (GI, intracranial).
  • High bleeding risk profile (HAS-BLED >=3).
  • Occupational or activity-related fall risk.
  • Patient preference after thorough counselling.

Not for:

  • Valvular AF (mechanical valves, moderate-severe MS).
  • LAA thrombus on pre-procedure TEE.
  • LAA anatomy that doesn’t accommodate the device range (very small, very ostial, multi-lobed with shallow depth).

Key procedural considerations

Sizing

  • Pre-procedure TEE / cardiac CT defines LAA ostium diameter and depth.
  • Choose a device 10-20% oversized to the ostial diameter.
  • Confirm sizing on intra-procedural TEE in all four standard views (0, 45, 90, 135 degrees).

Release criteria (PASS)

  • Position — distal shoulder distal to the ostium.
  • Anchor — gentle tug test confirms barb engagement.
  • Size — device compression 10-30%.
  • Seal — no peri-device leak >5 mm.

If any criterion fails, recapture (FLX is recapturable up to the shoulder marker), reposition, or upsize/downsize.

Trial context

  • PROTECT-AF and PREVAIL established WATCHMAN’s non-inferiority to warfarin for stroke prevention with a tradeoff of early procedural risk for long-term bleeding reduction.
  • PINNACLE FLX validated the FLX iteration on safety and seal endpoints.
  • Current US trials extend evidence into DOAC-comparison and very-high-bleeding-risk subgroups.

What to know in the lab

  • Transseptal puncture site matters: inferior and posterior to facilitate LAA access; high-anterior punctures fight the LAA orientation.
  • Maintain ACT >250 throughout the case.
  • Deair the delivery sheath meticulously — air embolism into the LA goes systemic.
  • TEE operator and EP operator must communicate at each deployment step; ICE is an alternative when TEE access is limited.
  • Confirm PASS criteria with both fluoroscopy and TEE before final release.

Post-implant management

  • 0-45 days: DAPT (aspirin + clopidogrel) or DOAC bridge per institutional protocol.
  • 45-day TEE: confirm no peri-device leak >5 mm and no device-related thrombus.
  • If sealed: transition to single antiplatelet (typically aspirin) long term.
  • If leak >5 mm or thrombus: continue anticoagulation, repeat imaging, consider additional closure if persistent.

Common issues & troubleshooting

  • Peri-device leak >5 mm — continue anticoagulation; consider vascular plug or coil for closure of persistent leak.
  • Device-related thrombus — reinstate anticoagulation; reimage at 4-8 weeks; usually resolves.
  • Pericardial effusion — most often from over-aggressive transseptal or shoulder protrusion. Immediate echo and pericardiocentesis setup ready.
  • Embolisation — extremely rare with proper sizing and PASS confirmation; surgical retrieval if it occurs.
  • Failed access — abandoned cases happen; document anatomy and reconsider device choice (Amulet may suit some anatomies better).

Manufacturer reference

Watch

Short videos to help illustrate this topic. Embedded from the original channels — content belongs to them.

WATCHMAN FLX implant · Boston Scientific EP

Last reviewed by Dr. Colombowala on May 22, 2026.

Not medical advice. This page is educational. Your situation may differ — discuss it with Dr. Colombowala or your treating physician before making decisions.

Source: