In patients with atrial fibrillation, which scenario requires warfarin therapy instead of DOACs?

• A. Valvular AF with a mechanical valve
• B. Nonvalvular AF with no valve disease
• C. Atrial fibrillation after valve repair that is not mechanical
• D. All AF patients can use DOACs

Answer: (A)

The key idea is that the type of valve determines which anticoagulant is appropriate. Mechanical prosthetic valves create a very high risk of thrombus formation because their artificial surface strongly activates clotting. For patients with atrial fibrillation who have a mechanical valve, the safest and most effective long-term option is warfarin with careful INR monitoring to keep the anticoagulation in the therapeutic range. DOACs, while convenient for many patients with nonvalvular AF, have not been proven safe or effective in those with mechanical valves; a major trial with a DOAC in this setting showed worse outcomes, so guidelines exclude DOACs here.

In contrast, DOACs are approved and commonly used for atrial fibrillation without mechanical valve disease and may be used after bioprosthetic valve implantation or valve repair, though the specifics can vary. The scenario that requires warfarin rather than a DOAC is AF with a mechanical valve.