Evaluation of the Hemocompatibility of the Direct Oral Anti-Coagulant Apixaban in Left Ventricular Assist Devices

Inclusion Criteria: 1. Patients implanted with a HeartMate 3 LVAD 2. Age 18 or greater and able to provide written informed consent 3. Females of childbearing age must agree to adequate contraception Exclusion Criteria: 1. History of post-LVAD device thrombosis, stroke, or gastrointestinal bleeding 2. Patients who are bridge to transplant and a current UNOS status 1-3 3. Ongoing inotrope therapy after LVAD (e.g., milrinone, dobutamine, epinephrine) 4. Permanent right ventricular assist device at the time of LVAD implant 5. Patients with a mechanical heart valve 6. Patients with end-stage renal disease on dialysis 7. Pregnant patients 8. Known history of ischemic stroke, intracranial bleed, or neurosurgery within 3 months 9. Known history of intracerebral arteriovenous malformation, cerebral aneurysm or mass lesions of the central nervous system. 10. Recent (\<48 hours) or planned spinal or epidural anesthesia or puncture 11. Prior history of known thrombophilia (e.g., factor V Leiden, prothrombin gene mutation, protein C or S deficiency, antithrombin 3 deficiency, hyperhomocysteinemia, antiphospholipid antibody syndrome) or indication for higher INR goal (\>2.5) with warfarin. 12. Thrombolysis within the previous 7 days 13. Patients with an allergy or contraindication to aspirin, warfarin, or apixaban 14. Patients on antiplatelet therapy other than aspirin (e.g., clopidogrel, prasugrel, ticagrelor, dipyridamole, or pentoxifylline) 15. Patients on combined P-glycoprotein and strong CPY3A4 inhibitors or inducers (e.g., fluconazole, posaconazole, rifampin) 16. Known bleeding within the last 30 days requiring emergency room presentation or hospitalization 17. Known history of an inherited bleeding disorder (e.g., hemophilia, von Willebrand disease) 18. Patients with active bleeding or a hemoglobin \< 8.0 g/dl 19. Total bilirubin \> 2.0 mg/dl, shock liver, hepatic encephalopathy, or biopsy proven liver cirrhosis 20. INR \> 2.0 not due to anticoagulation therapy 21. Platelet count \<100,000 cells/mm3