Catastrophic In-Stent Thrombosis with Antiphospholipid Syndrome: A case report

Background In-stent thrombosis despite morphologically optimal stents remains a diagnostic challenge. Antiphospholipid syndrome is a rare cause that drives thrombosis via tissue factor– mediated coagulation—a pathway not addressed by dual antiplatelet therapy. Case summary A 51-year-old male with cardiovascular risk factors underwent primary percutaneous coronary intervention for anterior ST-elevation myocardial infarction. Ten days later he developed refractory ventricular fibrillation requiring extracorporeal cardiopulmonary resuscitation with veno-arterial extracorporeal membrane oxygenation and intra-aortic balloon pump support. Emergency angiography confirmed complete in-stent thrombosis; intravascular ultrasound excluded a mechanical cause. The intensive care course revealed a triad of red flags: unexplained in-stent thrombosis, recurrent extracorporeal circuit clotting despite stepwise heparin escalation, and arterial and venous thrombosis on full anticoagulation. This prompted antiphospholipid antibody testing, which showed persistent moderate-to-high titre anti-cardiolipin IgM—a profile within the “controversial” zone of the 2023 ACR/EULAR classification criteria. The patient was managed as APS with intensified triple therapy, later transitioning from heparin to a vitamin K antagonist, and was discharged on day 27 with no events at 3-month follow-up. Conclusion APS should be considered in unexplained in-stent thrombosis even when laboratory criteria are not strictly met. The triad of unexplained in-stent thrombosis, anticoagulationrefractory circuit clotting, and incident venous thrombosis is a clinically actionable pattern warranting empiric APS-directed management.