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Management and Outcomes of Subtherapeutic Warfarin Anticoagulation in Patients with Antiphospholipid Syndrome and Mechanical Mitral Valves Sara R Vazquez1, 2, Stephen Short2, Spencer Gilbert1, 2, Daniel M Witt1, 2. 1University of Utah Health Thrombosis Service, Murray, UT, USA.2University of Utah College of Pharmacy, Salt Lake City, UT, USA

Abstract

Background: High thrombotic-risk patients taking warfarin [specifically, antiphospholipid syndrome (APS) and/or a mechanical mitral valve replacement (mMVR)] may experience periods of subtherapeutic anticoagulation (intentional or unintentional). In these scenarios, a bridging strategy with low molecular weight heparin (LMWH), may be used with the goal of preventing recurrent thrombosis, despite uncertain net clinical benefit. Objectives: The objective of this study is to describe the management practices and outcomes in a single academic medical center in these perceived high thrombotic risk patients who experience periods of subtherapeutic anticoagulation. Methods: Patients enrolled in the University of Utah Health Thrombosis Service with a validated diagnosis of APS or a mMVR and a laboratory-confirmed outpatient subtherapeutic International Normalized Ratio (INR) <1.7 between October 1, 2023, to October 31, 2024 were included. The indication for anticoagulation, concomitant conditions, reason for subtherapeutic INR (periprocedural hold or unexpected subtherapeutic INR), bridging strategy utilized, and 30-day clinical outcomes were obtained via manual review of the electronic medical record. Clinical outcomes in the 30 days after the index subtherapeutic INR included thromboembolism and clinically relevant bleeding (major or clinically relevant nonmajor bleeding). Results: During the study period there were 87 patients with APS (n=42), a mMVR (n=41 patients), or both (n= 4) who had 243 subtherapeutic INRs <1.7. The mean subtherapeutic INR in all patients was 1.39 (standard deviation [SD] 0.18). The majority of those subtherapeutic scenarios were unexpected subtherapeutic INRs (n=199, 81.9%), followed by intentional periprocedural warfarin holds (n=38, 15.6%), and intentional warfarin hold for bleeding symptoms (n=6, 2.5%). The majority of periprocedural INR scenarios used bridging (n=29 bridging, 76.3%), while the majority of unexpected subtherapeutic INR scenarios did not use bridging (n=40 bridging, 20.1%). The median time to re-achieve INR >2.0 was 7 days in the bridged group (interquartile range [IQR] 7) and 14 days in the non-bridged group (IQR 20). There were 10 adverse events among 6 patients in the 30 days after the bridging episode (3 thromboembolism, 7 clinically relevant bleeding), with 8 events occurring in the first 14 days. Two of these 10 adverse event scenarios included bridging. Three (n=2 thromboembolism) of these 10 adverse events occurred in the periprocedural group, and 7 (n=6 bleeding events) occurred in the unexpected subtherapeutic INR group. Conclusions: In a single academic medical center, high-thrombotic risk patients with antiphospholipid syndrome and/or mechanical mitral valve replacement taking warfarin were mostly bridged for periprocedural scenarios requiring warfarin reversal but not bridged for unexpected subtherapeutic INRs of <1.7. Adverse event rates were not correlated with the decision to either utilize or forego a bridging strategy. Future studies should investigate the net clinical benefit of bridging in these high-thrombotic risk populations.

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