What is the recommended antithrombotic regimen for a patient with a bioprosthesis after Aortic Valve Replacement (AVR) who is in sinus rhythm?

Antithrombotic Regimen Post-AVR with Bioprosthesis in Sinus Rhythm

For patients with a bioprosthetic aortic valve in sinus rhythm without other indications for anticoagulation, aspirin 75-100 mg daily is recommended over warfarin for the first 3 months, followed by lifelong aspirin therapy. 1

First 3 Months Post-Operative Period

Standard Surgical Bioprosthetic AVR

• Aspirin 50-100 mg daily is preferred over warfarin (Grade 2C recommendation) for patients in sinus rhythm with no other indication for vitamin K antagonist (VKA) therapy 1
• Warfarin with INR target 2.5 (range 2.0-3.0) may be reasonable as an alternative, though evidence shows no clear superiority over aspirin 1
• Both aspirin and warfarin groups should receive VTE prophylaxis-dose LMWH starting postoperative day 1 1

The evidence supporting aspirin over warfarin comes from randomized trials showing no significant difference in thromboembolic events (RR 0.89,95% CI 0.38-2.09) or bleeding (RR 0.50,95% CI 0.13-1.92) between the two strategies 1. The quality of this evidence is admittedly low due to small sample sizes and lack of blinding 1.

Transcatheter Aortic Valve Replacement (TAVR)

• Dual antiplatelet therapy with aspirin 75-100 mg plus clopidogrel 75 mg daily for 6 months is the standard approach, though based on clinical trial protocols rather than direct evidence 1, 2
• Warfarin for at least 3 months may be reasonable in patients at low bleeding risk, as subclinical valve thrombosis occurs in 7-40% of TAVR patients on antiplatelet therapy alone but not in those receiving warfarin 2
• After 6 months, transition to lifelong aspirin 75-100 mg daily alone 2

Long-Term Management (After 3 Months)

• Lifelong aspirin 75-100 mg daily is recommended for all patients with bioprosthetic aortic valves in sinus rhythm 1, 2, 3
• Long-term anticoagulation is NOT indicated unless other risk factors develop 1
• The long-term thromboembolic risk with bioprosthetic aortic valves is low (0.2%/year) in patients with sinus rhythm 1

Case series demonstrate excellent outcomes with aspirin alone: 145 patients in sinus rhythm on aspirin 75 mg daily had no major thromboembolic events and no major bleeding in 254 patient-years of follow-up 1.

High-Risk Subgroups Requiring Special Consideration

While the general recommendation favors aspirin alone, certain patient characteristics may warrant consideration of warfarin during the first 3 months:

• Female patients have higher thromboembolic risk (OR 2.23, p=0.005) but show reduction with either warfarin (OR 0.75, p=0.03) or aspirin (OR 0.66, p=0.02) 4
• Patients with 19-mm bioprosthetic valves have increased risk (OR 2.22, p=0.03) with significant benefit from warfarin (OR 0.65, p=0.02) or aspirin (OR 0.36, p=0.01) 4
• NYHA class III/IV patients show reduction in thromboembolism with warfarin (OR 0.73, p=0.04) 4
• Elderly patients (increasing age OR 1.03 per year, p=0.03) and those of short stature (OR 0.97, p=0.002) have elevated baseline risk 4

Indications for Chronic Anticoagulation

Warfarin with INR target 2.5 (range 2.0-3.0) is required long-term if any of the following develop:

• Atrial fibrillation (incidence as high as 16% at 31-36 months) 1, 2
• History of thromboembolism 1, 2
• Left ventricular dysfunction 1, 2
• Hypercoagulable conditions 1, 2
• Large left atrium 1

Contraindications

• Direct oral anticoagulants (DOACs) including dabigatran, apixaban, and rivaroxaban are contraindicated in patients with any prosthetic valve due to excessive thrombotic complications 1, 2, 5

Common Pitfalls and Caveats

• Do not extrapolate mitral bioprosthesis recommendations to aortic position: Mitral bioprostheses have much higher early thromboembolic risk (40 events per 100 patient-years in first month) and warrant warfarin for 3 months (Grade 2C) 1
• Inadequate anticoagulation in the early postoperative period may increase valve thrombosis risk, though this is primarily a concern for TAVR rather than surgical bioprostheses 3
• Subclinical leaflet thrombosis may not be detected by standard echocardiography, particularly relevant for TAVR patients 3
• Multiple observational studies show no benefit to early anticoagulation in low-risk surgical bioprosthetic AVR patients, with thromboembolic rates of 0.8-1.3% at 3 months regardless of aspirin use 4, 6
• Bleeding risk increases with warfarin without clear reduction in thromboembolic events in unselected populations 4, 7, 6