Abstract Body (Do not enter title and authors here): Background: Studies related to the Watchman device generally report data at the 45-day, 6-month, 1-year, and 2-year intervals, with outcomes supportive of Watchman closure. The imaging of the device at 45 days is believed to coincide with substantial completion of device endothelization and the end of the high risk period for device related thrombus (DRT). Thus, prophylactic systemic anticoagulation (SA) is often discontinued at this time.

Objective: To report the incidence of delayed DRT in patients following the 45 day post-implant imaging and the cessation of SA.

Methods: In this single center retrospective study, we assessed patients undergoing Watchman device placement between April 16, 2016, and June 30, 2022. Patient data was retrieved from our institutional Cardiovascular Data Registry database. Following Watchman device implantation, all patients underwent a 45-day surveillance TEE or CT. Our primary interest was assessing the incidence and timing of delayed DRT and determining the anti-platelet and/or SA regimen at the time of DRT.

Results: A total of 861 patients who underwent Watchman device placement were included in the study. The 45-day surveillance imaging revealed that 2.2% (19/861) of patients exhibited a DRT during the initial follow up imaging while on SA and aspirin (ASA). These patients continued on SA/ASA until the 6-month imaging, at which point 84% (16/19) patients showed DRT resolution. Among the 2 with persistent thrombus, one was on ASA/warfarin, while the other was on DAPT. The 3rd patient did not complete subsequent imaging after 45 days.

The patients without DRT at 45-day imaging had a 0.83% (7/842) incidence of DRT with 42.9% (3/7) revealed at 6 month, 42.9% (3/7) revealed at 12 months and the remaining 14.3% (1/7) at 24 month imaging. SAPT/SA protection was in place in 57.1% (4/7) of these cases, while the remainder were on SAPT 28.5% (2/7), or nothing at all 14.3% (1/7). Alarmingly, 2/7 of these cases resulted in an ischemic stroke in the absence of SA. In 85% of cases, DRT was associated with peridevice leak.

Conclusion: These findings underscore the importance of ongoing surveillance in patients with Watchman devices and do not suggest a clear association between continued anticoagulation therapy and reduced risk of delayed DRT formation. Further investigations are warranted to determine whether there are predictive patient or implant characteristics and elucidate optimal management strategies for this patient population.