Heparin Resistance in SARS-CoV-2 Infected Patients with Venous Thromboembolism

Effectiveness of different anticoagulation regimens in critically ill patients - experience from COVID 19 patients

This study compared the efficacy of therapeutic anticoagulation guided by anti-Xa levels vs. a D-dimer-based protocol in ICU patients with COVID-19. Given the heightened risk of thrombosis despite anticoagulation therapy in some cases, we hypothesised that anti-Xa measurement improves anticoagulation effectiveness and clinical outcomes in this population. We retrospectively analysed data from ICU patients at COVID Hospital Karaburma between April 2020 and December 2021. The primary outcome was the incidence of failed noninvasive ventilation necessitating intubation. Secondary endpoints included mortality rates, thromboembolic and bleeding complications, and anticoagulation effectiveness assessed by antifactor Xa activity. The analysis included 395 patients - 137 in the anti-Xa group and 258 in the D-dimer group. The D-dimer group showed a higher rate of failed noninvasive ventilation requiring intubation (65.7% vs. 50%, P  = 0.009). The overall mortality was 48.3%, significantly higher in the D-dimer group (52.7%) compared to the anti-Xa group (40.1%, P  = 0.02). Thromboembolic complications were lower in the anti-Xa group (2.9%) than in the D-dimer group (9.7%, P  = 0.014), with no significant difference in bleeding. Following the first LMWH administration, 70.8% of patients had anti-Xa levels below the therapeutic and 11.7% below the prophylactic range. Anti-Xa-guided anticoagulation improves survival and reduces thromboembolic complications compared to D-dimer-based treatment without increasing bleeding risk. This study highlights the potential of the anti-Xa assay in managing anticoagulation in critically ill COVID-19 patients. Our findings provide a foundation for future research on using anti-Xa measurements as a guiding tool to optimise anticoagulation therapy in other critically ill populations.

Troubleshooting heparin resistance

The term heparin resistance is likely best defined as the failure of an appropriate dose of unfractionated heparin (UFH) to achieve a predetermined level of anticoagulation. Unfortunately, and despite many prior reports, there is no established consensus as to what either the appropriate dose or the predetermined level should be. Traditionally, assays used to monitor anticoagulation with UFH have been clot based, including the activated partial thromboplastin time, used for patients on the ward or intensive care unit, and the activated clotting time, used for patients undergoing vascular interventions and cardiopulmonary bypass. Unfortunately, these tests may be highly influenced by other factors occurring in many patients, especially those with inflammation or acute infection, as noted during the COVID-19 pandemic. Many hospitals have thus moved to anti-Xa testing for heparin monitoring. Another important factor in defining heparin resistance includes dosing, whether weight-based or total daily dosing is used, as initial reports of heparin resistance described daily doses independent of body weight. Multiple causes of apparent heparin resistance include hypercoagulability, antithrombin deficiency, andexanet alfa used for direct oral anticoagulant reversal, thrombocytosis, and antiphospholipid antibody syndromes. Treatment options for managing patients with heparin resistance include weight-based dosing and administration of additional UFH, antithrombin supplementation, or the use of an alternative anticoagulant such as the direct thrombin inhibitors bivalirudin or argatroban.

Inhibition of sulfated glycans on the binding of dengue virus envelope protein to heparin

Dengue viruses (DENV) are transmitted to humans through mosquito bites and infect millions globally. DENV uses heparan sulfate (HS) for attachment and cell entry by binding the envelope protein to highly sulfated HS on target cells. Therefore, inhibiting the binding between DENV and HS could be a promising strategy for preventing DENV infection. In the current study, the interactions between DENV envelope protein (from Type 2 DENV) and heparin (a surrogate for HS) were analyzed using competition solution SPR. Results demonstrate that heparin binds to DENV envelope protein with high affinity (KD = 8.83 nM). Competitive Solution SPR assays using surface-immobilized heparin and a series of naturally-sourced and semi-synthetic sulfated glycans demonstrated significant inhibitory activity against the binding of DENV envelope proteins to heparin. This study of molecular interactions could provide insights into the development of therapeutics for DENV infection.

Defining heparin resistance: communication from the ISTH SSC Subcommittee of Perioperative and Critical Care Thrombosis and Hemostasis

The term heparin resistance (HR) is used by clinicians without specific criteria. We performed a literature search and surveyed our SSC membership to better define the term when applied to medical and intensive care unit patients. The most common heparin dosing strategy reported in the literature (53%) and by survey respondents (80.4%) was the use of weight-based dosing. Heparin monitoring results were similar based on the proportion of publications and respondents that reported the use of anti-Xa and activated partial thromboplastin time. The most common literature definition of HR was >35 000 U/d, but no consensus was reported among survey respondents regarding weight-based and the total dose of heparin when determining resistance. Respondent consensus on treating HR included antithrombin supplementation, direct thrombin inhibitors, or administering more heparin as the strategies available for treating HR. A range of definitions for HR exist. Given the common use of heparin weight-based dosing, future publications employing the term HR should include weight-based definitions, monitoring assay, and target level used. Further work is needed to develop a consensus for defining HR.