Are you or a loved one considering a prosthetic heart valve? It’s essential to understand the differences between mechanical and bioprosthetic valves, as well as what to consider when choosing one. This article breaks down the construction, function, and factors that influence a long-term treatment plan.

Understanding Prosthetic Heart Valves

A prosthetic heart valve aims to:

• Replicate the hemodynamics of natural valve functionality
• Minimize side effects such as thrombogenicity
• Optimize hemodynamics
• Ensure mechanical/biological durability
• Reduce biological response
• Provide an effective delivery system.

There are three main categories of prosthetic heart valves: mechanical, bioprosthetic, and homografts. These valves are used to replace damaged or malfunctioning natural heart valves. Each type of valve offers unique advantages and challenges, and the choice between them often depends on individual patient factors and preferences.

We will now examine the unique characteristics of the first two categories, mechanical and bioprosthetic valves.

Mechanical Valves

Mechanical valves, as their name suggests, are designed to mimic the function of natural heart valves, such as mitral valves, using mechanical parts. They come in three designs: caged ball, tilting disc (single leaflet), and bileaflet. These designs are part of the mechanical valve group.

The caged-ball design was the first type of mechanical valve, consisting of a silicone elastomer ball housed within a metal cage. The Starr-Edwards valve is the only FDA-approved example of this design. On the other hand, tilting disc valves include designs like the Medtronic Hall valve, which has a single circular occluder controlled by a metal strut. Other examples of tilting disc valves include the Omnicarbon and the discontinued Bjork-Shiley valves.

Introduced in 1979, bileaflet valves are the latest addition to the mechanical valve family. The St. Jude valve is the most commonly implanted mechanical valve in the United States. Other models include the CarboMedics and On-X valves. The unique advantages of each type of mechanical valve influence the selection, which is typically based on the patient’s specific needs and circumstances.

Bioprosthetic Valves

In contrast to mechanical valves, tissue valves, also known as bioprosthetic valves, are fashioned from biological tissue, such as porcine valves or bovine pericardium. These valves offer the advantage of being more “biocompatible,” reducing the risk of clot formation and the need for lifelong anticoagulation therapy.

Bioprosthetic valves come in two types: stented bioprosthetic valves and stentless models. Stented models are made from porcine aortic valves or bovine pericardial tissue, while stentless models offer improved hemodynamics over older stented models, although their long-term durability is uncertain.

Examples of porcine bioprosthetic valves include the Carpentier-Edwards, Hancock II, and Mosaic valves. On the other hand, examples of pericardial bioprosthetic valves include the Perimount series, Edwards Prima Plus, Medtronic Freestyle, and Toronto SPV valve. Patient’s specific needs and circumstances often dictate the choice between stented and stentless models.

Transcatheter Aortic Valve Replacement (TAVR)

Transcatheter Aortic Valve Replacement, or TAVR, also known as transcatheter aortic valve implantation (TAVI), is a minimally invasive procedure used to treat aortic stenosis. Since its first performance in 2002, TAVI has become a staple procedure in managing aortic stenosis and represents a considerable advancement in heart valve therapy, especially for younger patients.

The TAVR method involves less intrusive techniques. The procedure can be performed by guiding a catheter through the femoral artery or via a small incision in the chest wall. The new valve’s placement can be executed by expanding with a balloon or may involve a self-expanding valve, depending on the specific situation.

Compared to conventional open-heart surgery, TAVR generally results in a shorter hospital stay and quicker recovery. As a result, it has become an increasingly popular choice for aortic valve replacement, particularly in patients who are at high risk for traditional open-heart surgery.

Aortic Valve-in-Valve TAVR

The valve-in-valve TAVR procedure offers a minimally invasive option for patients whose bioprosthetic heart valves have failed, providing a necessary treatment typically 10 to 15 years after initial implantation. For high-risk patients who have already had open-heart surgery for surgical valve replacement, valve-in-valve TAVR is beneficial as it drastically reduces recovery time compared to another open-heart surgery.

The availability of transcatheter valve-in-valve implantation for failed bioprosthetic valves is an important consideration during initial valve selection, and is now included in Heart Team discussions for long-term planning. Potential adverse events following valve-in-valve implantation, such as suboptimal hemodynamics and limited coronary artery access, must be taken into account when selecting an initial prosthetic valve.

Valve Repair and Replacement Techniques

When it comes to treating heart valve diseases, there are two main surgical approaches: valve repair and valve replacement. Mitral valve repair is generally preferred over mitral valve replacement when a durable repair is possible. This is especially true in cases of degenerative mitral regurgitation due to its benefits of lower mortality, better left ventricular function preservation, and fewer valve-related complications.

The choice between repair and replacement is influenced by the etiology of the mitral valve disease, such as degenerative, ischemic, and rheumatic causes, and the patient’s specific condition. Mitral valve repair techniques may include leaflet repair, annuloplasty, and artificial chordae implantation, varying according to the underlying pathological changes of the valve.

On the other hand, mitral valve replacement entails the removal of the diseased valve and implantation of a mechanical or biologic prosthesis. The surgical approach chosen is based on the patient’s condition and available expertise. Various surgical approaches such as open-heart surgery, minimally invasive surgery, or robot-assisted surgery are options for MVR, with considerations for patient recovery and hospital stay.

Mitral Valve Repair

Mitral valve repair is the preferred surgical procedure for all types of mitral valve dysfunction, especially degenerative mitral regurgitation. Mitral valve repair is recommended (class IIa) for patients with chronic severe secondary mitral regurgitation who are undergoing coronary artery bypass grafting (CABG) or aortic valve replacement (AVR).

Techniques like leaflet repair with quadrangular resection and annuloplasty offer long-term durability and help reduce the likelihood of future reoperations. The patient’s specific needs and circumstances, along with the expertise and equipment available at the healthcare facility, often guide the decision to repair the mitral valve.

Mitral Valve Replacement

While mitral valve repair is often the preferred choice, there are situations when mitral valve replacement is indicated. This can be the case when mitral valve repair is not feasible or when the mitral valve is too damaged to repair, often due to calcification or rheumatic disease.

Conditions such as severe mitral regurgitation caused by papillary muscle rupture, degenerative and ischemic MR, or a failed repair undergoing reoperation can lead to the consideration of mitral valve replacement. The choice between mechanical and biologic prostheses for mitral valve replacement should be based on patient-specific factors like age, comorbidity, and the necessity of anticoagulation.

The surgical technique for mitral valve replacement involves an incision in the left atrium, followed by careful placement of the new valve to ensure proper function and avoid leaks. After mitral valve surgery, patients may be monitored in the ICU, require management of tubes for drainage, and need a specific care plan for incision sites.

Clinical Considerations for Prosthetic Valve Selection

Selecting the right prosthetic heart valve is a critical decision that needs to take into account a range of patient-specific factors. Patient age is a significant factor, reflecting a trade-off between bleeding risks and the need for reoperation. Mechanical valves are often recommended for younger patients, while bioprostheses are typically favored for older individuals or those contraindicated for anticoagulation.

Patient preference, alongside specific anatomic considerations like minimizing prosthesis-patient mismatch, also play a critical role in prosthetic valve choice. In some cases, annular enlargement may be necessary to ensure optimal prosthetic fit and function. In developing countries, factors extending beyond patient age, such as socioeconomic status, education, and geographic accessibility, are vital in selecting an appropriate prosthetic heart valve due to their influence on life expectancy and healthcare access.

Comorbid conditions including left ventricular dysfunction, pulmonary arterial hypertension, and atrial fibrillation reduce life expectancy and should be factored into the decision-making process for prosthetic valve selection. Remember, the selection of a prosthetic heart valve is a complex process that involves a wide range of factors. It should always be made in consultation with a healthcare professional.

Complications and Management of Prosthetic Valves

While prosthetic heart valves have revolutionized the treatment of heart valve disease, they are not without their complications. Prosthetic heart valve complications encompass:

• Primary valve failure
• Prosthetic valve endocarditis
• Thrombosis
• Mechanical hemolytic anemia
• Issues related to anticoagulation.

Clinical presentations of valve dysfunction can range from acute volume overload and pulmonary edema due to mitral valve prosthetic failure to dyspnea and heart failure symptoms from aortic valve failure, depending on the complication and type of valve. Prosthetic valve endocarditis is associated with high mortality, variable clinical symptoms, and specific complications, with mortality rates ranging from 25-40% in staphylococcal infections up to a staggering 93% in fungal etiologies.

Thromboembolic events related to prosthetic valves can present with varied symptoms such as sudden onset dyspnea to systemic embolization, with an occurrence rate of approximately 4.8% per patient year for mechanical valves. Management strategies for prosthetic valve complications include medical, surgical, and interventional therapies, addressing issues from periprosthetic regurgitation to major hemorrhage, with a focus on the reversal of anticoagulation and emergency valve replacement when necessary.

Bioprosthetic Valve Durability and Longevity

While bioprosthetic valves are increasingly favored due to their superior hemodynamics and reduced risk of thrombosis, their longevity is typically less than that of mechanical valves. However, recent improvements in bioprosthetic valve technology, such as the use of genetically modified porcine tissue, aim to enhance longevity and reduce the incidence of reoperation.

Younger patients, specifically those under 40 years old, are more prone to bioprosthetic valve degeneration with higher failure rates compared to older populations. Dealing with structural valve degeneration, calcification, and immune responses are pivotal factors that contribute to the longevity and durability of bioprosthetic valves.

Looking ahead, the Foldax Tria valve shows promise with minimal structural damage in accelerated wear testing, hinting at future directions for bioprosthetic valve development. Despite these advancements, bioprosthetic valves are still estimated to have a shorter functional lifespan, approximately 10-15 years, compared to over 30 years for mechanical valves. Note that mitral valve bioprostheses degenerate at a quicker rate compared to bioprosthetic aortic valves. This is a significant factor when evaluating durability and patient outcomes.

Anticoagulation Therapy for Mechanical Valves

While mechanical heart valves offer long-term durability and operational stability, they require lifelong anticoagulation therapy due to their increased thrombogenicity. The incidence of thrombosis with mechanical valves varies from 0.1-5.7% per patient-year, while the risk of anticoagulation-related hemorrhagic events is approximately 4.5% per patient year, with an incidence of major hemorrhagic complications of 1-3% per year.

The challenges in anticoagulation therapy include maintaining the therapeutic range of INR, managing drug interactions, and ensuring patient adherence to the treatment plan to minimize the risk of thromboembolic and hemorrhagic complications. For patients with mechanical heart valves, the target INR is set within 1.5-2.0 for aortic valve replacements (AVR) and 2.5-3.0 for mitral valve replacements (MVR) and double valve replacements (DVR).

Innovations and Future Developments in Prosthetic Heart Valves

The field of prosthetic heart valves is not static and is constantly evolving as scientists and engineers strive to overcome the limitations presented by mechanical and bioprosthetic valves. Polymeric heart valves are being developed to offer potential benefits in reduced thrombogenicity and the elimination of lifelong anticoagulation.

Advanced polymer compositions like polycarbonate urethanes and nanocomposite materials are being utilized for heart valves to optimize hemocompatibility, reduce thrombotic risks, and enhance durability. Materials such as Hastalex and other polymeric compounds have demonstrated significant biostability and biocompatibility, resisting calcification and potentially reducing immune responses.

The only FDA-approved Total Artificial Heart, the SynCardia™, exemplifies innovation with its capacity to replace biventricular heart function and sustain substantial blood flows for end-stage heart failure patients. Despite these advancements, there is an ongoing need to make bioprosthetic heart valve surgery not only more durable for a variety of patient populations but also more affordable and accessible.

Frequently Asked Questions

What is the life expectancy of a prosthetic heart valve?

The life expectancy of a prosthetic mechanical heart valve is typically 20 years or more, as they tend not to wear out quickly.

What is the difference between mechanical and prosthetic heart valve?

The main difference between a mechanical and prosthetic heart valve lies in their durability and the need for long-term blood-thinning medication. Mechanical valves last longer but require lifelong anticoagulation with warfarin, while bioprosthetic valves are less durable but do not carry the same risk of blood clots.

Is there an artificial heart valve?

Yes, an artificial heart valve can be implanted using a less invasive transcatheter approach, depending on the valve that needs replacement.

What are the main types of prosthetic heart valves?

The main types of prosthetic heart valves are mechanical and bioprosthetic valves, with mechanical valves being made from durable materials and bioprosthetic valves being made from biological tissues. Choose the type that suits your needs best.

What is Transcatheter Aortic Valve Replacement (TAVR)?

TAVR is a minimally invasive procedure that replaces a narrowed aortic valve to treat aortic stenosis. It doesn't require open-heart surgery.