Prevention of mechanical valve thrombosis with a combination of the factor Xa inhibitor edoxaban plus aspirin in swine: intermediate results from the EdoValves project
Authors: Castelli F M , Besola L , Fiocco A , Fanelli G N , Delle Donne M G , Carpentieri A , Recchia F , Colli A , Burchielli S , De Caterina R 
Published: October 2024

Abstract

Background
Patients with an implanted mechanical heart valve (MHV) currently have a contraindication to the use of non-vitamin K antagonist oral anticoagulants (NOACs) based on the unfavorable results of the RE-ALIGN trial with dabigatran. We hypothesized that the combination of a Factor Xa inhibitor, acting upstream of thrombin generation, plus aspirin, may effectively prevent valve thrombosis, providing a much more friendly and viable alternative to vitamin K antagonists for such patients. We tested this in a swine model with a recently implanted mechanical valve prosthesis in the mitral position, combining the most unfavorable conditions promoting mechanical valve thrombosis, based on (a) the implanting position; (b) recent surgery; (c) the high thrombogenicity of the animal model. The study was approved by the Animal Ethics Committee of the University of Pisa and the Italian Ministry of Health and conducted according to Good Clinical Practices for Animal Experiments.

Methods
17 farm male pigs, weighing ≈30 kg at the beginning, underwent cardiac surgery under general anesthesia and with extracorporeal circulation to receive a 25 mm or 27 mm bileaflet Corcym Bicarbon mechanical heart valve replacement in the mitral position. Pigs were given 1 mg/kg enoxaparin immediately after surgery and started with the oral daily administration of edoxaban 1 mg/kg (30 mg, then escalated to 60 mg with the animal growth) + aspirin 100 mg, both given as crushed tablets with a food pellet since the animal awakening from anesthesia. An initially planned warfarin control group was quickly abandoned because of the extreme difficulty of controlling warfarin activity. Animals were submitted to blood sampling and transthoracic echocardiography at least twice in the follow-up when uneventful for up to three months or in case of health deterioration. The autopsy was performed by a certified pathologist after each spontaneous death or procured sacrifice.
Results (Figure 1): Excluding 5 peri-operative deaths, 12 animals survived surgery. Of those, 6 died within the second month: pulmonary edema occurred in 3 cases, due to prosthesis-mismatch in the growing animals; pulmonary infection occurred in 1 subject; heart failure due to valve thrombosis occurred in 2 cases. Six swine were full-term survivors in good health status up to the 3-month planned observational time. No hemorrhagic events were ever documented.

Conclusion
The combination of edoxaban + aspirin effectively avoided valve thrombosis events in 10 out of 12 (83%) analyzable animals and was safe from bleeding complications. The study is ongoing up to a predicted sample size of ≥20 animals. If further confirmed, these data may open the possibility of an alternative to vitamin K antagonists in humans with the fixed-dose drug combination here used, without the need for continuous anticoagulation monitoring and with expected greater safety.Figure 1