Artificial heart valves: types

An artificial (prosthetic) valve is a device that replaces a damaged heart valve and restores one-way blood flow. Classically, a distinction is made between mechanical and biological (bioprosthetic) valves. Mechanical valves are made of ultra-strong materials (carbon, titanium) and last for decades, but require lifelong anticoagulation. Bioprosthetic valves are created from processed tissue (usually bovine/porcine pericardium or xenovascular valves); they are quieter and do not always require long-term anticoagulation, but they wear out over time (structural degeneration) and more often require repeat interventions. The choice is always a balance between durability and the need to thin the blood. [1]

Prostheses operate according to the same hydrodynamic principles as native valves: the leaflets open under the pressure of blood flow and close completely when the pressure gradient reverses. In mechanical valves, this cycle is achieved by two half-disks (bileaflets) or a rotating disc; in bioprostheses, flexible leaflets, either with or without a stent, are used. An important parameter is the effective orifice area: the larger it is, the lower the pressure gradient and the lower the risk of patient-prosthesis mismatch. In practice, this is taken into account when selecting the size and model for a specific anatomy. [2]

Over the past 15 years, a revolution has occurred with the advent of catheter-based valves (TAVI/TAVR for the aortic position and a growing line of transmitral/transtricuspid solutions). These are inserted through the femoral artery without major surgery or cardiopulmonary bypass. For elderly and high-risk patients, this has become the standard, and for those under 75, the choice between catheter-based and surgical replacement is individualized based on anatomy, expected longevity, and the likelihood of repeat procedures. [3]

Finally, a prosthesis is more than just a piece of hardware or tissue. It's a part of a lifelong journey: after implantation, the patient lives with a monitoring plan (echocardiography, anticoagulation monitoring during mechanical procedures, endocarditis prophylaxis) and pre-discussed "what-ifs" (pregnancy, dentistry/surgery, sports, repeat interventions). Current recommendations emphasize: the decision is made jointly with the patient ("shared decision-making"), taking into account their values and plans. [4]

Types of valves: materials, form factors, where appropriate

Mechanical valves (bicuspid carbon) are the benchmark for durability: in young patients, they are practically "lifelong." The price is strict anticoagulation with warfarin (usually a target INR of 2.5-3.5, depending on the position and risk factors). An exception is the On-X valve in the aortic position: the PROACT study demonstrated a safe, lower INR of 1.5-2.0 in combination with aspirin in carefully selected patients. This reduces bleeding without increasing thrombosis, but requires discipline and proper selection. Direct oral anticoagulants (DOACs) are contraindicated for mechanical valves, following the RE-ALIGN study. [5]

Bioprosthetic valves—pericardial or xenovascular valves—are more convenient in terms of drug load: 3 months after surgical implantation, an antiplatelet agent is sufficient for most patients (unless there are other indications for anticoagulation). They are quieter, better tolerated psychoemotionally, and are preferable when planning pregnancy, but they deteriorate more often in young patients (calcification, leaflet ruptures). For the aortic position, transfemoral TAVI valves are increasingly used in the elderly (usually ≥75 years) and in high/moderate-risk patients; durability in younger patients remains a matter of debate, but 8-10-year data are encouraging and comparable to surgery in a number of studies/registries. [6]

Based on fixation, bioprostheses are classified as stent-based or stentless, rapid-deployment/sutureless to reduce ischemia and cardiopulmonary bypass, and, in the catheter world, self-expanding and balloon-expandable designs. Valve-in-valve is increasingly being used to "repair" degraded bioprostheses: a new catheter-based valve is installed in the worn-out valve without a repeat "major" operation. This has expanded the horizons for patients who chose a bioprosthesis in their youth, but it is important to consider the size and future compatibility in advance. [7]

A separate branch is tricuspid and mitral catheter therapy: in addition to complete replacement (TMVR/TTVR), repair methods (clips, rings, chordal solutions) are now routinely used. These are particularly useful for functional regurgitation and in patients at high risk for open surgery. The choice of technology is determined by the "heart team" after a multi-imaging assessment. [8]

Table 1. Mechanical vs. bioprosthesis: what is important at the start

Criterion	Mechanical	Bioprosthesis
Durability	Maximum (decades)	Limited (wears out faster in young people)
Anticoagulation	Lifelong warfarin (On-X: reduced INR as indicated)	Often only short-term; then antiplatelet agent
Noise/quality of life	The clicking of the shutters is possible	Quiet
Repeated interventions	Rarely, but more difficult	Most likely; "valve-in-valve" as an option

How to Choose a Valve: Age, Plans, Risks, and Plan B

Recommendations discourage chasing after a "perfect fit for all" option. Age is an important, but not the only, factor: the younger the patient, the stronger the arguments for mechanical (durability); the older the patient, the greater the comfort and lower drug load of a bioprosthesis. However, it's not the years in the patient's passport that decide the outcome, but the patient's profile: life expectancy, comorbidities, readiness and ability to manage INR, bleeding risk, pregnancy plans, lifestyle, and availability of repeat procedures. [9]

In the aortic position, in patients over 75 years of age and/or with a high surgical risk, TAVI is the preferred route; for those aged 65-75 years, the choice is individual; in those under 65, surgery (SAVR) is more often preferred, with an eye on durability and the calculation of the "ladder" of repeat interventions. In the mitral position, surgery still predominates in younger patients, with repair (if repair is possible) prioritized over replacement; if replacement is necessary, the choice between a mechanical or bioprosthetic valve again comes down to lifestyle and anticoagulation. [10]

For patients of reproductive age planning pregnancy, a bioprosthesis is more often recommended (to avoid warfarin, which is teratogenic in the first trimester), with a frank discussion about the likelihood of earlier degradation and the potential for valve-in-valve failure. For patients with absolute indications for lifelong anticoagulation (e.g., AF with a high risk of stroke), a mechanical valve may be more logical, as warfarin is still needed. [11]

Finally, a roadmap for revision procedures is important. If a bioprosthesis is chosen at age 50-60, the team checks in advance whether a valve-in-valve can be safely placed (the diameter of the "inner ring," the risk of coronary obstruction, and access to the coronaries), and what to do if a valve-in-valve-in-valve is needed. This "B/V plan" makes the decision informed and reduces surprises 10-15 years later. [12]

How valves are installed: surgery and catheter approaches

Surgical replacement (SAVR/MVR) is performed open-heart surgery with short-term artificial circulation. The surgeon removes the leaflets, sutures the prosthesis to the fibrous ring, checks for leaks and gradients, and closes the access site. The advent of rapid-deployment/sutureless replacement has reduced ischemia and CPB time—useful for complex surgeries and in fragile patients. Quality control is achieved by intraoperative transesophageal echocardiography. [13]

TAVI/TAVR is performed through the femoral artery under X-ray and echo guidance: a catheter with a valve is advanced into the narrowed aortic position and expanded (using a balloon or self-inflating). In elderly patients, this is most often an outpatient or short-term hospital stay. Limitations include anatomy (narrow "exit ring," high risk of coronary obstruction, bilaterian valves, etc.). With good anatomy and preparation, TAVI demonstrates excellent 1-5-year outcomes; the question of 10-year longevity in younger patients remains unclear, although early data and observations (e.g., NOTION) are encouraging. [14]

For the mitral/tricuspid position, the range of catheter solutions is growing: from repair (clips, annuloplasty) to complete replacement (TMVR/TTVR) in high-risk patients requiring open surgery. Preoperative planning relies on multi-imaging: CT planimetry, TEE/3D-Echo to assess the annulus, chords, risk of LVOT obstruction, and coronary access. [15]

An important detail is the center's infrastructure and "heart team": where cardiac surgeons, interventional cardiologists, anesthesiologists, and imaging experts work together, complications are lower and long-term outcomes are better. This is one of the hidden quality factors, rarely visible to the patient but very noticeable in the long run. [16]

Life with a prosthesis: medications, monitoring, everyday life

If you have a mechanical valve, the basic rule is warfarin forever (DOACs are contraindicated for mechanical valves). The target INR depends on the valve position and risk factors (usually 2.5-3.5; for aortic On-X, 1.5-2.0 is acceptable in selected patients, plus aspirin according to protocol). Regular INR checks, nutrition education (vitamin K), an "anticoagulation passport," and discussion of "bridges" for surgery/dental procedures are required. [17]

With a bioprosthesis, short-term anticoagulation (for the first 3 months after surgical implantation) or immediate antiplatelet therapy is usually sufficient—the details depend on the position and accompanying indications (e.g., atrial fibrillation). After TAVI, the antithrombotic therapy strategy is individualized: for many, aspirin monotherapy is sufficient, while for other indications, an anticoagulant is added, according to the center's current protocols. All these decisions are documented in writing to ensure that the patient and family physician are not left with ambiguous interpretations. [18]

Prevention of infective endocarditis remains important, as dental procedures are a risk factor. Current guidelines identify patients who require antibiotic prophylaxis before invasive dentistry; oral and skin care guidelines are discussed at discharge. Annual echocardiography is standard for all prostheses, and if new symptoms (shortness of breath, fever, or murmur) develop, it is performed unscheduled. [19]

In everyday life, most restrictions are common sense: regular aerobic exercise, strength training—by agreement (especially in the first months), traveling with a "valve passport" and a list of medications, a reminder about MRI compatibility (modern valves are MRI-compatible; metal "clips" and valve frames are not a contraindication). The "clicking" sound of a mechanical valve is normal; if it suddenly disappears or changes, this is a reason to contact the center. [20]

Table 2. Antithrombotic therapy after valve replacement (essence)

Situation	Basic strategy
Mechanical valve	Warfarin for life (INR by position/risk); DOAC - no
On-X aortic (selected)	INR 1.5-2.0 + aspirin according to the center's protocol (after the starting period)
Surgical bioprosthesis	3 months of anticoagulation or antiplatelet agent → then antiplatelet agent (unless otherwise indicated)
TAVI	Often monoaspirin; if OAC is indicated - OAC in monotherapy

Potential problems and how to solve them

Mechanical valve thrombosis or thromboembolism are rare but critical events. Prevention consists of appropriate INR and adherence. If thrombosis does occur, the strategy depends on the thrombus's position, size, hemodynamics, and risk: surgery or ultraslow low-dose thrombolysis in patients at high surgical risk (gathering evidence and discussed in recent publications). After the event, target INRs and risk factors are reassessed. [21]

With bioprostheses, the main long-term problem is structural degeneration: calcification, thickening/rupture of the leaflets, gradient increase, or regurgitation after 8-15 years (faster in young people, slower in the elderly). The modern "plan B" is valve-in-valve (catheter implantation of a new valve into the old one) with a short rehabilitation period; sometimes special techniques are required (for example, dissection of the "fracture" framework) for an optimal opening. [22]

Infective endocarditis of prosthetic valves remains a serious risk: it requires early diagnosis (blood cultures + TEE/PET-CT as indicated), a combination of antibiotics, and often reoperation. Prevention (dental, skin, "clean" procedures) is more effective than any "retroactive" therapy. [23]

Finally, prosthesis-patient misfit (PPM) and conduction system damage (more common after TAVI – requiring permanent pacing) are common applied issues. Their incidence is reduced by careful CT planning, proper size/model selection, and careful implantation technique. All these details are part of the "center's quality." [24]

Table 3. What can go wrong - and what to do

Problem	What is visible	What are they doing?
Thrombosis of mechanics	Gradient increase/“sticking” of valves, shortness of breath	Surgery or ultraslow thrombolysis in high-risk patients
Degeneration of a bioprosthesis	Gradient↑/regurgitation↑	Valve-in-valve or surgery
Endocarditis	Fever, bacteremia, vegetations	Antibiotics + often reoperation
Block after TAVI	Bradycardia, pauses	Permanent pacemaker

What's Next: Innovations and Horizons

The longevity of TAVI is extending beyond the 10-year horizon: the first randomized data (NOTION et al.) showed a comparable or even better rate of severe structural degeneration compared to surgery at the 10-year mark in the elderly; attention is now shifting to younger patients and "multi-stage" approaches (SAVR → TAVI-in-SAVR, TAVI → TAVI-in-TAVI). The decision is still individual and depends on anatomy and life expectancy. [25]

Work is underway on polymer and tissue-engineered valves designed for mechanical durability without the need for warfarin, as well as on "rejuvenating" bioprostheses (anti-calcification treatments, modified crosslinkers). While this is still in research phase, the first clinical signals are already emerging. [26]

In the mitral and tricuspid catheter areas, there is an explosive growth in devices: combined "repair and replacement" strategies, new methods for preventing LVOT obstruction (LAMPOON-like techniques), and improved anchor systems. All of this will expand access to minimally invasive care for patients previously considered "inoperable." [27]

Finally, antithrombotic strategies are improving: warfarin is still the gold standard for mechanical therapy (and this is unlikely to change anytime soon), but ultraslow thrombolysis protocols for thrombosis and refined target INRs for individual models (such as On-X) are making therapy safer. For TAVI, the consensus is shifting toward minimally sufficient therapy (often monoaspirin) to reduce bleeding without increasing thrombosis. [28]