Prosthetic Heart Valves and Anticoagulation
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Direct answer
Prosthetic heart valves are artificial valves, either mechanical or bioprosthetic, and mechanical valves need lifelong warfarin to prevent valve thrombosis and embolism. The usual INR target is 2.5 for a mechanical aortic valve without risk factors and 3.0 for a mechanical mitral valve or when additional thromboembolic risk is present, while bioprosthetic valves need shorter anticoagulation. Warfarin is embryopathic, so pregnant women with mechanical valves are commonly switched to low molecular weight heparin in early pregnancy.
What you must remember
- Mechanical valves: durable but need lifelong anticoagulation, with bileaflet designs the most common.
- Bioprosthetic valves: less thrombogenic, and usually need anticoagulation only for a short period after surgery unless another indication is present.
- Aortic INR target: 2.5, with a range of 2.0 to 3.0, for a mechanical aortic valve without risk factors.
- Mitral INR target: 3.0, with a range of 2.5 to 3.5, for a mechanical mitral valve or when risk factors such as atrial fibrillation are present.
- DOACs: not used with mechanical valves, since trial evidence showed excess thromboembolism and bleeding.
- Valve thrombosis: presents with a muffled or absent valve click, new obstruction or embolism, and needs urgent imaging.
- Pregnancy: warfarin is embryopathic, so early pregnancy is managed with heparin, with warfarin often resumed later.
- Infection risk: prosthetic valve endocarditis is a serious complication, which is why dental prophylaxis matters for these patients.
Anticoagulating a woman with a mechanical valve who plans pregnancy
A 32-year-old woman with a mechanical mitral valve takes warfarin and wants to conceive. Her echocardiogram is stable and her valve function is normal.
- Plan before conception: Early counselling allows a planned switch of anticoagulant, since warfarin exposure in early pregnancy carries a risk of embryopathy.
- Switch in early pregnancy: Warfarin is replaced by weight-adjusted low molecular weight heparin or unfractionated heparin, with anti-Xa monitoring in some centres.
- Reassess later in pregnancy: Many centres resume warfarin in mid-pregnancy and switch back to heparin before delivery, following current guidance.
- Plan delivery: Anticoagulation around labour is planned in advance, because neuraxial anaesthesia needs timing adjustments when heparin is used.
- Restart after delivery: Warfarin is resumed postpartum, with an INR target matched to the valve position.
- Monitor valve function: Regular echocardiography checks the valve gradients and looks for thrombosis throughout pregnancy.
Anticoagulation must be balanced against bleeding, because the pregnancy plan changes the risk of both valve thrombosis and haemorrhage. Lifelong follow-up in an anticoagulation clinic keeps the INR within target between pregnancies.
Where the exam tries to catch you
Valve questions test INR targets and anticoagulant choice in special situations.
- Trap: Prescribing a DOAC for a mechanical valve. Correct: DOACs are not used with mechanical valves, and warfarin is the standard.
- Trap: Using an INR target of 2.5 for a mechanical mitral valve. Correct: The mitral mechanical target is 3.0, with a range of 2.5 to 3.5, which is higher than the aortic target.
- Trap: Continuing warfarin unchanged in early pregnancy. Correct: Warfarin is embryopathic, so heparin is used in early pregnancy.
- Trap: Treating a muffled valve click as a normal finding. Correct: Muffled clicks suggest valve thrombosis and require urgent imaging.
Frequently asked questions
What INR target is used for a mechanical aortic valve?
A mechanical aortic valve without additional risk factors is usually targeted at an INR of 2.5, with a range of 2.0 to 3.0. Risk factors such as atrial fibrillation or previous thromboembolism may call for a higher target.
Why are DOACs not used with mechanical heart valves?
Direct oral anticoagulants are not used with mechanical heart valves because trial evidence showed excess thromboembolism and bleeding with a DOAC in this setting. Warfarin remains the standard anticoagulant for mechanical valves.
How does valve thrombosis usually present?
Valve thrombosis usually presents with a muffled or absent mechanical click, new breathlessness or signs of embolism. Fluoroscopy and echocardiography, including transoesophageal echo, help confirm the diagnosis and guide urgent treatment.
Which anticoagulant is used in pregnancy for a woman with a mechanical valve?
Low molecular weight heparin or unfractionated heparin replaces warfarin in early pregnancy, because warfarin carries a risk of embryopathy. The regimen is adjusted through pregnancy and planned around delivery and neuraxial anaesthesia.