Subtherapeutic INR Mechanical Valve — EECC MCQ

Correct answer: B — Subtherapeutic INR with a mechanical mitral valve carries a high risk of valve thrombosis (mitral > aortic position) — increase warfarin dose, consider short-term bridging with LMWH if INR is significantly below target, recheck INR within 2-3 days, and investigate the cause of the low INR

Subtherapeutic anticoagulation with a mechanical valve is dangerous — valve thrombosis can cause acute obstruction (haemodynamic emergency) or thromboembolism (stroke). The mitral position is higher risk than aortic because: (1) lower flow velocity across the mitral valve; (2) larger valve surface area; (3) proximity to the LA (where stasis occurs in AF). Management of subtherapeutic INR per ESC 2025 VHD Guidelines: (1) investigate cause: missed doses, drug interactions (enzyme inducers — rifampicin, carbamazepine), dietary changes (increased vitamin K intake), diarrhoea/malabsorption; (2) increase warfarin dose; (3) if INR is significantly below target (<1.5 for a 2.5-3.5 target): consider LMWH bridging until INR is therapeutic; (4) recheck INR within 2-3 days; (5) reinforce adherence counselling. The goal is to minimise the duration of subtherapeutic anticoagulation.

Reference: ESC/EACTS (2025): VHD Guidelines