How do we manage thrombogenicity and thrombosis in the Fontan? New Horizons...

Fontan circulation is a profoundly prothrombotic state and thrombosis is a major cause of death in patients with Fontan circulation.

Many thrombotic events in Fontan patients are subclinical but clinically significant.

The cumulative hazard risk of thrombotic events in Fontan patients increases over time, with Fontan circulation becoming essentially a freight train of thrombogenicity.

Fontan circulation's thrombotic risk is comparable to paroxysmal nocturnal hemoglobinuria (30-40% risk over 5 years), antiphospholipid antibody syndrome, and unprovoked venous thromboembolism (20-30% recurrence rate).

Relative hypoxia and loss of pulsatile flow in the venous system is very thrombogenic for endothelial cells.

Hypoxia and loss of pulsatile flow result in upregulation of tissue factor expression (the primary initiator of the clotting cascade), upregulation of adhesion molecules that activate inflammatory cells, and increased secretion of factor VIII and von Willebrand factor.

Protein-losing enteropathy (PLE) results in increased inflammatory system activation in Fontan patients.

Liver synthetic dysfunction can develop over time in Fontan patients and worsen hemostatic system activation.

Overall data supports that warfarin is better thromboprophylaxis than aspirin in Fontan patients.

Excellent time-in-therapeutic-range above 80% with warfarin is achievable using a paternalistic approach with aggressive monitoring and phone follow-up.

Even with well-managed anticoagulation, the bleeding risk is around 2% per year.

Warfarin is very problematic from a pharmacokinetic standpoint and poorly managed warfarin may actually increase thrombotic risk.

Direct oral anticoagulants (DOACs) such as rivaroxaban and apixaban seem superior to warfarin in many ways but are completely unproven in Fontan patients.

The honeymoon phase duration can vary and may be predictable using biomarkers.

Elevated factor VIII is a strong marker of increased thrombotic risk and can be elevated due to genetic factors, endothelial cell activation, or as an acute phase reactant indicating inflammation.

Fontan circulation, even in the context of liver dysfunction, shifts the hemostatic balance toward a thrombophilic state.

Monitoring D-dimer, factor VIII, liver function tests, and albumin every 6 months can predict when the honeymoon period of relatively low thrombotic risk is ending.

Aspirin VerifyNow is an extremely reliable and reproducible test that confirms patients are taking aspirin and having an antiplatelet response.

DOACs need to be studied in the Fontan population before determining how good or bad they are.

To use DOACs routinely in Fontan patients, reliable monitoring methods are needed because organ function can change rapidly in these patients.

DOACs are most likely better than poorly controlled warfarin, but high time-in-therapeutic-range is achievable with warfarin in most patients.