Mechanical Aortic Valve Replacement
Aortic valve stenosis is the most common type of valvular heart disease in the elderly. The incidence of aortic valve disease increases with age; one in eight people over the age of 75 have moderate to severe valvular heart disease. The natural history of aortic stenosis usually begins with an asymptomatic period with the development of symptoms once the valve is critically stenosed. The progression of stenotic valve and time of onset of symptoms varies from patient to patient. Symptomatic patients with severe stenosis have a poor prognosis. Ross first described the higher mortality rate after the onset of cardiac symptoms in 1968.
Aortic valve replacement (AVR) has shown to substantially improve survival in patients with symptomatic severe aortic stenosis, and this has formed the basis for recommending aortic valve replacement (AVR) in such circumstances. Currently, there are two techniques being used for aortic valve replacement; mechanical or bioprosthetic valve replacement via open-heart surgery and cardiopulmonary bypass and minimally invasive mechanical valve via a transcatheter (TAVR) approach.
The three main types of artificial heart valves are mechanical, bioprosthetic, and tissue-engineered valves. The mechanical heart valve is composed of strong, durable material, bioprosthetic valves are created from animal valves or part of animal tissue that is strong and flexible, and tissue-engineered valves are grown in-vitro using seeding human cells on to the scaffold. We will be discussing mechanical heart valves in this article.
There are three main types of mechanical valves that are used so far.
- Caged ball valve: First artificial heart valve that used a metal cage to house a silicone elastomer ball. When the heart contracts and the pressure in the chamber exceed more than the atrial, the ball inside raises to the top of the cage and prevents blood flow. When the heart finishes contracting and the pressure inside the chamber drops, the ball falls back to the base of the cage and allows blood flow. Caged ball valves have a high tendency to form blood clots and imposed higher hemodynamic consequences, and are no longer used.
- Tilting disc valve: This is a type of swing check valve, made by a metal ring, which holds the disc and is covered by the fabric where sutures are applied to place the valve. It opens when the chamber pressure drops to pump the blood out and closes to prevent the backflow of the blood. Medtronic-Hall model is the most common tilting-disc design in the US.
- Bi-leaflet heart valves: These are the most commonly used mechanical valve prostheses. This valve consists of two semicircular leaflets. They are considered the least thrombogenic of mechanical valves and are characterized by washing regurgitant blood jets.
The major advantage of the mechanical heart valve is its durability, as it can last for approximately 20 years, but it increases the risk of blood clot formation and can cause mechanical hemolytic anemia.
Anatomy and Physiology
Earn CME credit as you help guide your clinical decisions.
The heart consists of 4 valves separating four chambers of the heart and its outlets - aortic, pulmonic, mitral, and the tricuspid valve. Aorta is the largest artery in the body and originates from the left ventricle. The aortic valve lies between the left ventricle and the aorta. The aortic valve typically has three cusps and that are named after their attachment and vicinity to the other structures. Bicuspid valves are not uncommon with 1 to 2% of the population has congenital two leaflets.
Rarely, Valves with congenital four and single cusp have also been reported. The left coronary cusp covers the left coronary sinus and origin of the left main coronary artery, the right coronary cusp covers the right coronary sinus and origin of the right coronary artery, and the non-coronary cusp covers the non-coronary sinus towards the interatrial septum. In adults, the normal aortic valve area is 3.0 to 4.0 cm2. The three aortic valve leaflets open and close with each heartbeat for a one-way flow of blood from the left ventricle to the aorta.
Transthoracic and transesophageal echocardiography are the two best tools to evaluate the aortic valve morphology. There are strict criteria outlined by the American Society of Echocardiography for severe aortic stenosis and the need for aortic valve replacement. Severe aortic stenosis is described as follows:
- Aortic valve area of less than or equal to 1.0 cm2
- Mean transvalvular aortic gradient greater or equal to 40 mmHg
- The maximum aortic jet velocity of greater than equal to 4 m/s across the valve
- Severe high-gradient aortic stenosis with symptoms by either history or on exercise testing (stage D1).
- Asymptomatic patients with severe AS (stage C2) and left ventricular ejection fraction (LVEF) <50 %.
- Patients with severe AS (stage C or D) undergoing other cardiac surgery.
- Asymptomatic patients with severe AS and low surgical risk.
- Asymptomatic patients with severe AS and decreased exercise tolerance or fall in systemic blood pressure.
A mechanical valve is preferable over a bioprosthetic valve in the following patients:
- Surgical aortic valve replacement in patients age < 55 years old.
- No contraindication to anticoagulation with Vitamin K antagonist.
- An existing indication for anticoagulation like a prosthetic mechanical valve at a different location.
- High risk of morbidity and mortality with reintervention.
- Concomitant cardiac diseases can further compromise myocardial function such as poor left ventricular ejection fraction (LVEF), previous cardiac surgery, and associated coronary artery disease (CAD).
- Neurological dysfunction
- Chronic lung disease or terminal end-organ lung dysfunction
- Liver cirrhosis or terminal end-organ liver dysfunction
- Renal insufficiency
- Recent stroke within the last six months
- Severe pulmonary hypertension with right ventricular dysfunction
- Echocardiographic evidence of an intracardiac mass, thrombus, or vegetation
- Life expectancy less than 12 months owing to a noncardiac cause
- Myocardial infarction within the last 30 days
Mechanical aortic valve replacement requires open-heart surgery with cardiopulmonary bypass. Any contraindication to cardiopulmonary bypass and higher frailty index making the patient an unsuitable candidate for the cardiopulmonary bypass should be considered as a contraindication for mechanical aortic valve replacement. In this case, the patient should be evaluated for transcatheter valve replacement.
The following equipment is required for the procedure:
- Cardiopulmonary bypass machine
- The valve prosthesis of various sizes
- Transesophageal echocardiography
- Surgical instruments
The following staff is needed to carry out aortic valve replacement:
- Cardiothoracic Surgeon
- Cardiac Anesthesiologist
- Industry representative (for newer valves)
An interprofessional heart team evaluates and prepares the patient for the procedure.
The heart team:
- Cardiologist and interventional cardiologist
- Cardiothoracic surgeons
- Cardiac anesthesiologist
Technique or Treatment
There are two major types of replacement techniques: surgical aortic valve replacement (sAVR) and transcatheter aortic valve replacement (TAVR). TAVR is the minimally invasive surgical technique for aortic valve replacement for patients who are not a candidate for sAVR.
- Minimally Invasive Surgical Aortic Valve Replacement
- Right Anterior Mini Thoracotomy
- Mini sternotomy
- Conventional sternotomy and valve replacement
- Two FDA approved valves in the United States: SAPIEN valves (Edwards Lifesciences) and the CORE-valves (Medtronic)
- The newest generation Medtronic valve is the EVOLUTE-R. It has the ability to self expand and repositioning after deployment.
Mechanical aortic valves are more prone to thromboembolic complications compared to bioprosthetic valves (1% to 2% vs 0.7%) and bleeding complications due to the requirement of long-term anticoagulation to avoid thromboembolic events e.g. stroke, acute leg ischemia, or visceral embolization. If the INR is high, the patient is at risk of bleeding complications.
Endocarditis is a known complication of prosthetic heart valves and may occur early or late. The hallmark of prosthetic valve endocarditis with mechanical aortic valves is a ring abscess, which gradually leads to a perivalvular leak and valve dehiscence. If the abscess extends inferiorly, it can cause a conduction block.
The mechanical aortic valve has a finite life span of 15 to 20 years. Hence, these patients sometimes need a second aortic valve replacement, especially if done at a younger age.
Patients with malfunctioning mechanical valves may present with dyspnea, chest pain, syncope, or heart block.
Patients with acute valvular failure due to breakage of the components usually are hemodynamically unstable and need emergent replacement.
Aortic valve replacement is one of the most commonly performed procedures in patients with aortic stenosis. Mechanical aortic valves are the most durable and last long-term, thus reducing the need for re-operation. The mechanical aortic valve requires life-long anticoagulation. Initially, frequent follow-up with a cardiologist to adjust the INR is required, followed by interval follow-up to assess complications. To prevent thrombus formation, the INR should be maintained between 2 and 3. Patients with atrial fibrillation may need a higher INR. The ideal test to assess the function of a mechanical valve is an echocardiogram. Blood work usually reveals anemia in patients with mechanical aortic valves.
Enhancing Healthcare Team Outcomes
Aortic stenosis is a potentially serious condition affecting blood flow from the heart to the rest of the body. Calcification and atherosclerosis of the valve is the most common cause of aortic stenosis. It is well recognized that medical treatment has poor outcomes in patients with symptomatic AS with a mortality rate of 25% and 50% at 1 year and 2 years, respectively. Symptoms associated with severe aortic stenosis are angina, exertional dyspnea, dizziness or presyncope, and syncope. Over the past 6 decades, surgical aortic valve replacement was a gold standard for high-risk patients. Indications for aortic valve replacement has changed tremendously. Series of landmark clinical trials have shown a beneficial effect in intermediate to low-risk patients.
Mechanical and bioprosthetic valves are the most commonly used valves. Indications for different types of valves vary based on multiple factors. The choice of a prosthetic heart valve and the type of surgical approach should be based on shared decision-making between interprofessional teams, including cardiologists and surgeons. The factors such as long-term anticoagulation, the potential need for reoperation in the future, and the patient’s preference should be considered in the choice of prosthesis. The Interprofessional team should also consider the patient’s age, medical comorbidities, valve durability, risk of thromboembolic and bleeding complication, and risk of mortality.
Bouma BJ,van Den Brink RB,van Der Meulen JH,Verheul HA,Cheriex EC,Hamer HP,Dekker E,Lie KI,Tijssen JG, To operate or not on elderly patients with aortic stenosis: the decision and its consequences. Heart (British Cardiac Society). 1999 Aug; [PubMed PMID: 10409526]
Nishimura RA,Otto CM,Bonow RO,Carabello BA,Erwin JP 3rd,Guyton RA,O'Gara PT,Ruiz CE,Skubas NJ,Sorajja P,Sundt TM 3rd,Thomas JD, 2014 AHA/ACC guideline for the management of patients with valvular heart disease: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. Journal of the American College of Cardiology. 2014 Jun 10; [PubMed PMID: 24603191]Level 1 (high-level) evidence
Lim WY,Lloyd G,Bhattacharyya S, Mechanical and surgical bioprosthetic valve thrombosis. Heart (British Cardiac Society). 2017 Dec; [PubMed PMID: 28780576]
Eltchaninoff H,Durand E,Barbanti M,Abdel-Wahab M, TAVI and valve performance: update on definitions, durability, transcatheter heart valve failure modes and management. EuroIntervention : journal of EuroPCR in collaboration with the Working Group on Interventional Cardiology of the European Society of Cardiology. 2018 Aug 31; [PubMed PMID: 30158097]
Williams DS, Bicuspid aortic valve. Journal of insurance medicine (New York, N.Y.). 2006; [PubMed PMID: 16642647]
Kunihara T, Anatomy of the aortic root: implications for aortic root reconstruction. General thoracic and cardiovascular surgery. 2017 Sep; [PubMed PMID: 28656518]
Baumgartner H Chair,Hung J Co-Chair,Bermejo J,Chambers JB,Edvardsen T,Goldstein S,Lancellotti P,LeFevre M,Miller F Jr,Otto CM, Recommendations on the echocardiographic assessment of aortic valve stenosis: a focused update from the European Association of Cardiovascular Imaging and the American Society of Echocardiography. European heart journal cardiovascular Imaging. 2017 Mar 1; [PubMed PMID: 28363204]
Nishimura RA,Otto CM,Bonow RO,Carabello BA,Erwin JP 3rd,Guyton RA,O'Gara PT,Ruiz CE,Skubas NJ,Sorajja P,Sundt TM 3rd,Thomas JD,Anderson JL,Halperin JL,Albert NM,Bozkurt B,Brindis RG,Creager MA,Curtis LH,DeMets D,Guyton RA,Hochman JS,Kovacs RJ,Ohman EM,Pressler SJ,Sellke FW,Shen WK,Stevenson WG,Yancy CW, 2014 AHA/ACC guideline for the management of patients with valvular heart disease: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. The Journal of thoracic and cardiovascular surgery. 2014 Jul; [PubMed PMID: 24939033]Level 1 (high-level) evidence
Nishimura RA,Otto CM,Bonow RO,Carabello BA,Erwin JP 3rd,Fleisher LA,Jneid H,Mack MJ,McLeod CJ,O'Gara PT,Rigolin VH,Sundt TM 3rd,Thompson A, 2017 AHA/ACC Focused Update of the 2014 AHA/ACC Guideline for the Management of Patients With Valvular Heart Disease: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines. Journal of the American College of Cardiology. 2017 Jul 11; [PubMed PMID: 28315732]Level 1 (high-level) evidence
Baumgartner H,Falk V,Bax JJ,De Bonis M,Hamm C,Holm PJ,Iung B,Lancellotti P,Lansac E,Rodriguez Muñoz D,Rosenhek R,Sjögren J,Tornos Mas P,Vahanian A,Walther T,Wendler O,Windecker S,Zamorano JL, 2017 ESC/EACTS Guidelines for the management of valvular heart disease. European heart journal. 2017 Sep 21; [PubMed PMID: 28886619]
Lund O,Bland M, Risk-corrected impact of mechanical versus bioprosthetic valves on long-term mortality after aortic valve replacement. The Journal of thoracic and cardiovascular surgery. 2006 Jul; [PubMed PMID: 16798297]
Ashikhmina EA,Schaff HV,Dearani JA,Sundt TM 3rd,Suri RM,Park SJ,Burkhart HM,Li Z,Daly RC, Aortic valve replacement in the elderly: determinants of late outcome. Circulation. 2011 Aug 30; [PubMed PMID: 21824918]
Fatehi Hassanabad A,Vasanthan V,Kent WDT, Minimally Invasive Surgical Aortic Valve Replacement: An Overview of Recent Advances. The Canadian journal of cardiology. 2019 Feb; [PubMed PMID: 30760431]Level 3 (low-level) evidence
D'Onofrio A,Rizzoli G,Messina A,Alfieri O,Lorusso R,Salizzoni S,Glauber M,Di Bartolomeo R,Besola L,Rinaldi M,Troise G,Gerosa G, Conventional surgery, sutureless valves, and transapical aortic valve replacement: what is the best option for patients with aortic valve stenosis? A multicenter, propensity-matched analysis. The Journal of thoracic and cardiovascular surgery. 2013 Nov; [PubMed PMID: 24021955]
Tarride JE,Luong T,Goodall G,Burke N,Blackhouse G, A Canadian cost-effectiveness analysis of SAPIEN 3 transcatheter aortic valve implantation compared with surgery, in intermediate and high-risk severe aortic stenosis patients. ClinicoEconomics and outcomes research : CEOR. 2019; [PubMed PMID: 31551658]
Wang Y,Chen S,Shi J,Li G,Dong N, Mid- to long-term outcome comparison of the Medtronic Hancock II and bi-leaflet mechanical aortic valve replacement in patients younger than 60 years of age: a propensity-matched analysis. Interactive cardiovascular and thoracic surgery. 2016 Mar [PubMed PMID: 26675564]
Thaden JJ,Nkomo VT,Enriquez-Sarano M, The global burden of aortic stenosis. Progress in cardiovascular diseases. 2014 May-Jun; [PubMed PMID: 24838132]
Leon MB,Smith CR,Mack M,Miller DC,Moses JW,Svensson LG,Tuzcu EM,Webb JG,Fontana GP,Makkar RR,Brown DL,Block PC,Guyton RA,Pichard AD,Bavaria JE,Herrmann HC,Douglas PS,Petersen JL,Akin JJ,Anderson WN,Wang D,Pocock S, Transcatheter aortic-valve implantation for aortic stenosis in patients who cannot undergo surgery. The New England journal of medicine. 2010 Oct 21; [PubMed PMID: 20961243]
Thourani VH,Forcillo J,Szeto WY,Kodali SK,Blackstone EH,Lowry AM,Semple M,Rajeswaran J,Makkar RR,Williams MR,Bavaria JE,Herrmann HC,Maniar HS,Babaliaros VC,Smith CR,Trento A,Corso PJ,Pichard AD,Miller DC,Svensson LG,Kapadia S,Ailawadi G,Suri RM,Greason KL,Hahn RT,Jaber WA,Alu MC,Leon MB,Mack MJ, Outcomes in 937 Intermediate-Risk Patients Undergoing Surgical Aortic Valve Replacement in PARTNER-2A. The Annals of thoracic surgery. 2018 May; [PubMed PMID: 29253463]