Early device-related thrombosis after WATCHMAN™ FLX Pro implantation requiring surgical excision in essential thrombocythemia.

Left atrial appendage occlusion is an alternative therapy to oral anticoagulation for patients with non-valvular atrial fibrillation. Despite design refinements, device-related thrombus (DRT) remains a clinical concern, even with the latest WATCHMAN FLX Pro device (Boston Scientific, Marlborough, MA, USA). We report a case of surgical removal of the WATCHMAN FLX Pro device due to DRT. Despite appropriate antithrombotic therapy, a 77-year-old patient developed DRT leading to cardioembolic cerebral infarction. The thrombus was initially small and nonmobile but rapidly progressed over 45 days to a large, pedunculated, highly mobile thrombus with minimum attachment to the device, necessitating urgent surgical intervention. Subsequent hematologic evaluation revealed previously unrecognized essential thrombocythemia as the underlying prothrombotic condition. This case demonstrates that DRT can occur in patients with unrecognized prothrombotic conditions. Preprocedural thrombophilia screening should be considered in patients with suggestive clinical or laboratory findings, such as unexplained thrombocytosis, along with careful post implantation monitoring. Learning objectives: •Preprocedural evaluation for underlying prothrombotic disorders, including essential thrombocythemia, should be considered in patients with suggestive clinical or laboratory findings, such as ischemic stroke despite adequate anticoagulation or unexplained thrombocytosis.•Careful post-procedural monitoring is essential, as initially low-risk device-related thrombus may progress rapidly to high-risk forms requiring surgical intervention.