What is the recommended duration of aspirin (acetylsalicylic acid) therapy after mechanical valve replacement?

Aspirin Therapy After Mechanical Valve Replacement

For patients with mechanical heart valve prostheses, aspirin 75-100 mg daily is recommended lifelong in addition to anticoagulation with a vitamin K antagonist (VKA). 1

Antithrombotic Regimen for Mechanical Valves

Primary Anticoagulation

• All patients with mechanical valves require lifelong anticoagulation with a VKA (warfarin) 1
• INR targets depend on valve type and position:
  • Mechanical bileaflet or current-generation single-tilting disk aortic valve with no risk factors: INR 2.5 (range 2.0-3.0) 1
  • Mechanical aortic valve with risk factors (AF, previous thromboembolism, LV dysfunction, hypercoagulable state) or older-generation prosthesis: INR 3.0 (range 2.5-3.5) 1
  • Mechanical mitral valve replacement: INR 3.0 (range 2.5-3.5) 1

Aspirin Addition

• Aspirin 75-100 mg daily is recommended in addition to VKA therapy for all patients with mechanical valve prostheses 1
• This combination therapy provides superior protection against thromboembolic events compared to VKA alone 2
• The addition of aspirin to VKA has been shown to reduce mortality, particularly from vascular causes, and major systemic embolism 2

Special Considerations

Bleeding Risk

• When adding aspirin to VKA therapy, there is a modest increase in bleeding risk (primarily minor bleeding) 2
• However, the benefit of reduced thromboembolic events outweighs this bleeding risk 2
• For patients with high bleeding risk, careful monitoring is essential, but aspirin should still be continued if possible 3

Specific Valve Types

• For patients with the On-X mechanical aortic valve replacement and no thromboembolic risk factors:
  • Standard anticoagulation (INR 2.5, range 2.0-3.0) plus aspirin for the first 3 months after surgery
  • After 3 months, a lower INR target (1.5-2.0) with continued aspirin 75-100 mg daily may be reasonable 1, 4

Dual Antiplatelet Therapy

• Dual antiplatelet therapy (DAPT) without anticoagulation is NOT recommended for mechanical valves
• A clinical trial testing DAPT (aspirin plus clopidogrel) without warfarin was terminated early due to excess cerebral thromboembolic events 5

Important Warnings and Pitfalls

• Direct oral anticoagulants (DOACs) should NOT be used in patients with mechanical valve prostheses 1
• Never discontinue anticoagulation in patients with mechanical valves, as this significantly increases thrombotic risk 3
• For minor procedures (dental extractions, cataract removal), VKA should be continued at therapeutic levels 1
• If a patient with a mechanical valve experiences a stroke or systemic embolic event while on therapeutic VKA:
  • For aortic valve: Consider increasing INR target from 2.5 to 3.0
  • For mitral valve: Consider increasing INR target from 3.0 to 4.0 1

In summary, lifelong aspirin therapy at 75-100 mg daily is recommended for all patients with mechanical heart valve prostheses, in addition to appropriate VKA anticoagulation with target INR based on valve type, position, and patient risk factors.