6th May 2025

Prosthetic valves

The term prosthetic valve refers to non-native valves inserted in the place (or indeed inside) of a defective valve. These valves are typically divided up into the following:

• Mechanical
• Bioprosthetic
• Transcatheter

Mechanical and bioprosthetic valves can be implanted in any location, while transcatheter valves are typically reserved for the aortic and pulmonary positions, though mitral valves have also been attempted. Bioprosethetic valves can also be called xenografts given they contain biological material from another species.

A side note are homografts and autografts – homografts are valves taken from deceased donors, while autografts are the patients’ own valves, excised and reimplanted in an alternative location. 

Homografts are not commonly used due to their lack of availability, though they have at least equal outcomes in comparison to xenografts. Autografts are most commonly used in the Ross procedure – use of the pulmonary valve transposed into the aortic position with an aortic homograft.

Mechanical valves

Mechanical valves are synthetic, typically a mix of carbon and metal, and come in a variety of designs and sizes. In the absence of complications, their lifespan can outlast that of the patient but they require lifelong anticoagulation with a vitamin K antagonist such as warfarin as DOACs have been shown to be less effective. The INR target range is dependent upon patient and anatomical factors, with valves in the mitral position typically requiring higher INR targets (typically 3-4) due to the lower flow velocity compared to the aortic position (typically 2.5-3.5). Complications of mechanical valves include bleeding, infection of prosthetic material, dehiscence of the valve and obstruction of the valve due to clot. 

Bleeding can occur in the setting of excess anticoagulation, while any prosthetic material in the body serves as a nidus for infection, thus all patients with prosthetic material are advised to be rigorous in their dental hygiene and to avoid tattoos and piercings where possible to avoid a potential route for the seeding of bacteria. Dehiscence (or displacement) of the valve can occur in the context of endocarditis, or less commonly due to ineffective suturing coming loose. Obstruction of the valve due to clot is an emergency as it will lead to haemodynamic collapse if it significantly impedes flow and will need treatment with either lysis via heparinisation or thrombolytics, or emergency valve surgery. This is typically demonstrated by evidence of higher velocity flow through the valve with evidence of reduced or arrested valve leaflet motion on imaging tests.

Bioprosthetic valves

Bioprosthetic valves are typically made of bovine or porcine pericardium. Their lifespan typically sits in the range of between 10-20 years, with certain factors such as hypertension, hyperparathyroidism, end stage renal disease and diabetes mellitus reducing durability and valve lifespan. Unlike mechanical valve replacement there is a lack of clear evidence on the need for anticoagulation. European guidelines suggest that in the absence of other reasons for anticoagulation, either aspirin or a VKA can be considered for the first 3 months after a biological prosthesis is inserted in the aortic position, while VKA should be considered for the first three months for those with a biological prosthesis in the mitral or tricuspid positions. 

Complications are as above for mechanical prosthesis, though thrombosis is less commonly encountered. They remain a nidus for infection given the prosthetic material and lack of good blood flow to the valves.

Transcatheter valves

Transcatheter valves are those implanted through a catheter, most commonly in the aortic position. The benefit of these valves compared to those above is that they don’t require open cardiac surgery. As such, they can be considered in patients who have contraindications to surgery, including those with significant comorbidities and frailty. 

For the aortic TAVI there are a number of approaches, but transfemoral is overwhelmingly the most common. In this approach, a catheter is inserted into the femoral artery under local anaesthetic and sedation and fed retrogradely into the aortic position. Balloon valvuloplasty is performed, then under rapid pacing (to stop LV systolic flow displacing the new valve) a new valve is deployed in the aortic position and the catheter is removed. Newer versions of these valves are typically self-expandable. 

Given that they are performed under local anaesthetic and sedation, patients can typically be considered for discharge within 48 hours if there are no immediate complications. Common complications of TAVI can include conduction system abnormalities requiring need for pacing, alongside wound site issues with bleeding or infection. 

Subsequent to transcatheter aortic valve implantation, patients will typically be given a low dose single antiplatelet drug lifelong, commonly aspirin.

Choosing between valve types

Transcatheter valves are used less commonly, and typically only in the aortic and occasionally in the pulmonary position. In the aortic position TAVR is typically preferred if patients are >75 years or unsuitable for SAVR due to comorbidities or surgical risk, while SAVR is preferred if <75 years or low surgical risk.

Within surgical replacement, guidelines recommend mechanical prostheses if:

• According to patient preference
• Risk of accelerated valve dysfunction – young patients <40, hyperparathyroidism, dialysis patients
• <60 years for prosthesis in the aortic position, <65 years in the mitral position
• Patients for whom redo surgery or future TAVI would be high risk

Bioprosthetic valves are recommended if:

• According to patient preference
• Anticoagulation adherence is likely to be poor or contraindicated – typically due to high bleeding risk
• Young women considering pregnancy due to the teratogenic nature of vitamin k antagonists
• Life expectancy is lower than the presumed durability of the bioprosthesis
• In case of re-operation for mechanical valve thrombosis despite good anticoagulant adherence
• >65 years in the aortic position or >70 in the mitral position