Aortic valve replacement

Aortic valve replacement
ICD-9-CM	35.21-35.22V43.3

Aortic valve replacement is a procedure whereby the failing aortic valve of a patient's heart is replaced with an artificial heart valve. The aortic valve may need to be replaced because:

• The valve is leaky (aortic insufficiency, also known as aortic regurgitation),
• The valve is narrowed and doesn't open fully (aortic stenosis)

Current methods for aortic valve replacement include open heart surgery, minimally invasive cardiac surgery (MICS) and transcatheter aortic valve replacement (TAVR).

History

During the late 1940s and early 1950s, the first surgical approaches towards treating aortic valve stenosis had limited success. The first attempts were valvotomies, (i.e. cutting the valve while the heart is pumping). A ball valve prosthesis placed on the descending thoracic aorta (heterotopically) was developed by Hufnagel, Harvey and others to address aortic stenosis, but had disastrous complications. Later, with the innovation of cardiopulmonary bypass, the ball valve prosthesis was placed orthotopically (i.e. in same place as the original aortic valve). This first generation of prosthetic valves was durable, but needed intense anti-coagulation, and cardiac hemodynamics were compromised. During the mid-1950s, a single-leaflet prosthesis was developed by Bahnson et al. In early 1960, Ross and Barratt-Boyes used allografts. Tissue prosthetic valves were introduced in 1965 by Binet in Paris, but they degenerated quickly because of the tissue was insufficiently preserved. Carpentier solved this problem by introducing glutaraldehyde-preserved stent-mounted porcine valves.

Anatomy, physiology and pathophysiology

Classification of aortic stenosis severity

U/S findings	Mild	Moderate	Severe
Aortic valve area, cm2	>1.5	1.0-1.5	<1.0
Aortic valve area index, cm2/m2	-	-	0.6
Mean pressure gradient, mmHg	25	25-40	>40
Peak jet velocity, m/s	<3	3-4	>4

Classification of Aortic Regurgitation Severity

U/S findings	Mild	Moderate	Severe
Jet width of Left ventricular outflow tract	<25%	25%-65%	>65%
Vena contracta width cm	<0,3	0,3-0,6	0,6
Regurgitant volume mL per beat	<30	30-49	60
Regurgitant fraction (%)	30	30-49	>50
Regurgitant orifice area (cm2)	<0,10	0,10-0,30	>o,30

The aortic valve is semilunar with three cusps. It separates the heart from the aorta. Each cusp is attached to the aortic wall in such a manner to create a sinus, a Valsalva sinus. The origins of the two coronary arteries are sited in two valsalva sinuses, each one named after the coronary artery that is supplying. Leaflets are separated among them by commissures. The posterior leaflet is in continuation with the anterior leaflet of the mitral valve (the tissue is called aorto-mitral curtain). The aortic valve is opened during systole, the driving force for it to open is the difference in the pressure between the contracting Left Ventricle of the heart and the aorta. During cardiac diastole (when the heart chamber gets bigger) the aortic valve closes.

Aortic stenosis most commonly is the result of calcification of the cusps. Other reasons of stenosis is the bicuspid valve (instead of 3, some patients have only 2 cusps at the aortic valve) and rheumatic aortic stenosis (now rare in the West). In any case, the obstruction at the level of the Aortic Valve causes increased pressure within the left ventricle of the heart which leads to hypertrophy and ultimately dysfunction of the heart. While x-ray and ECG might give some subtle hints of Aortic Stenosis, echocardiography is the diagnostic procedure of choice. US findings also help in grading the severity of the disease. In cases of symptomatic Severe Aortic Stenosis, AVR is warranted. In cases of asymptomatic but severe Aortic Stenosis, more factors should be taken into consideration.

Aortic regurgitation, on the other hand, has many causes: Degeneration of the cusps, endocarditis, Bicuspid aortic valve, aortic root dilatation, trauma, connective tissue disorders such as Marfan syndrome or Ehlers-Danlos lead to imperfect closure of the valve during diastole, hence the blood is returning from the Aorta towards the left ventricle of the heart. Acute aortic regurgitation (caused by endocarditis, aortic dissection or trauma) ends up in pulmonary oedema, because of the acute increase in Left ventricle (LVEDP) that does not have time to adjust to the regurgitation. Chronic regurgitation, by contrast, gives time to heart to change shape, resulting in eccentric hypertrophy, which has disastrous effects on the myocardium. Ultrasound is here also the best diagnostic mobility, either it is transthoracic or transesophageal.

When is aortic valve replacement the appropriate treatment?

Guidelines for aortic valve replacement

As long-term data on the survival and quality of life of people following valve replacement have become available, evidence-based guidelines for aortic valve replacement have been developed. These help healthcare professionals decide when aortic valve replacement is the best option for a patient. Two widely accepted sets of guidelines used by surgeons and cardiologists are the American Heart Association and American College of Cardiology Guidelines for the Management of Patients with Valvular Heart Disease, and the European Society of Cardiology and the European Association for Cardio‑Thoracic Surgery Guidelines for the management of valvular heart disease.

Aortic stenosis

Aortic stenosis is treated with aortic valve replacement in order to avoid angina, syncope, or congestive heart failure. Individuals with severe aortic stenosis are candidates for aortic valve replacement once they develop symptoms or when their heart function is impacted. Some people with asymptomatic aortic stenosis may also be candidates for aortic valve replacement, especially if symptoms appear during exercise testing. Patients with moderate aortic valve stenosis who need another type of cardiac surgery (i.e. coronary artery bypass surgery) should also have their valve addressed by the surgical team if echocardiography unveils significant heart problems.

Low gradient aortic stenosis with concomitant left ventricular dysfunction poses a significant question to the surgeon and the patient. Stress echocardiography (i.e. with dobutamine infusion) can help determine if the ventricle is dysfunctional because of aortic stenosis, or because the myocardium lost its ability to contract.

Aortic insufficiency

Many people with aortic insufficiency often don’t develop symptoms until they have had the condition for many years. Aortic valve replacement is indicated for symptoms such as shortness of breath, and in cases where the heart has begun to enlarge (dilate) from pumping the increased volume of blood that leaks back through the valve.

Types of valves

Main article: Artificial heart valve

There are two basic types of replacement heart valve: tissue (bioprosthetic) valves and mechanical valves.

Tissue valves

Tissue heart valves are usually made from animal tissue (heterografts) mounted on a metal or polymer support. Bovine (cow) tissue is most commonly used, but some are made from porcine (pig) tissue. The tissue is treated to prevent rejection and calcification (where calcium builds up on the replacement valve and stops it working properly).

Occasionally, alternatives to animal tissue valves are used: aortic homografts and pulmonary autografts. An aortic homograft is an aortic valve from a human donor, retrieved either after their death or from their heart if they are undergoing a heart transplant. A pulmonary autograft, also known as the Ross procedure is where the aortic valve is removed and replaced with the patient's own pulmonary valve. A pulmonary homograft (a pulmonary valve taken from a cadaver) is then used to replace the patient's own pulmonary valve. This procedure was first performed in 1967 and is used primarily in children, as it allows the patient's own pulmonary valve (now in the aortic position) to grow with the child.

Tissue valves can last 10–20 years. However, they tend to deteriorate more quickly in younger patients.

Tissue valves come as stented or stentless. Stented valves come in sizes from 19mm to 29mm. Stentless tissue are directly sutured at the aortic root. Their major advantage is that they create a better patient-prosthesis mismatch and can be helpful when dealing with small aortic root. Their disadvantage is that it more time-consuming to implant stentless valves while the patient is on the machine.

Mechanical valves

Mechanical valves are designed to outlast the patient, and have typically been stress-tested to last several hundred years. Although mechanical valves are long-lasting and generally present a one-surgery solution, there is an increased risk of blood clots forming with mechanical valves. As a result, mechanical valve recipients must take anticoagulant (blood thinning) drugs such as warfarin for the rest of their lives, making the patient more prone to bleeding.

Valve selection

Selecting the appropriate valve is greatly influenced by the age of the patient. Other factors that are taken into consideration are probable contra-indication to warfarin, the will of the female patient to give birth to a child in the future, life expectancy, the body size, lifestyle consideration and patient preference.Worth noting that in young patients and during pregnancy, tissue valves deteriorate rapidly. When a tissue valve wears out and needs replacement, the person must undergo another valve replacement surgery. For this reason, younger patients often receive mechanical valves to prevent the increased risk (and inconvenience) of another valve replacement. Generally, a patient under 60 years old gets a mechanical valve, above 70 gets a tissue valve and between 60 and 70 years old, other factors are taken into consideration.

Procedure

Surgical Procedure

Diagram of the opened heart, viewed from the front. The aortic valve separates the left ventricle from the aorta.

Heart viewed from above, with atria removed to expose the valves.

Aortic valve replacement is most frequently done through a median sternotomy, meaning the incision is made by cutting through the sternum. Once the pericardium has been opened, the patient is canulated (aortic cannulation by a cannula placed on the Aorta and a venous canulation by a single atrial venous cannula inserted through the right atrium. The patient is put on a cardiopulmonary bypass machine, also known as the heart-lung machine. This machine takes over the task of breathing for the patient and pumping their blood around while the surgeon replaces the heart valve. A Y-type cardioplegic infusion catheter is also placed on the Aorta, de-aired and connected to the CP machine. One more route for delivering cardioplegia could be utilized, by the retrograde cardioplegic cannula inserted at the Coronary Sinus. Some surgeons also opt to place a vent in the Left Ventricle through Right Superior Pulmonary Vein,- it helps preventing of left ventricular distention before and after the cardiac arrest. When the setup is ready, a crossclamp is applied at distal ascending Aorta, cardioplegia is infused and the aorta is incised milometers above the Sino-Tubular Junction (a little above the origin of the ostia)- it is called aortotomy. Once aortotomy is made, cardioplegia is delivered directly through the ostia.

The heart is now still and the surgeon removes the patient's diseased aortic valve. The cusps of the Aortic Valve are excised and the aortic anulus is debrided from calcium. Sutures are place in the annulus, most commonly braided 2-0 with plegets, although various techniques have been described. A decision is made on what kind of valve (prosthetic, allograft or autograft) will be inserted. A prosthetic valve is the most common choice, by far. Surgeon measures the diameter of the aortic ring, so a mechanical or tissue of an appropriate size is put in its place. Sutures are then are passed through the prosthetic valve, the prosthetic is slowly seated to the aortic ring and sutures are secured. Sometimes, when aortic root is very small, in order to gain some extra space the sutures are not place at the annulus but outside of the aortic root. Once the valve is in place and the aorta has been closed, patient is placed in a Trendelenburg position and the heart is de-aired. Then the patient is taken off the heart-lung machine. Transesophageal echocardiogram (TEE, an ultra-sound of the heart done through the esophagus) can be used to verify that the new valve is functioning properly. Pacing wires are usually put in place, so that the heart can be manually paced should any complications arise after surgery. Drainage tubes are also inserted to drain fluids from the chest and pericardium following surgery. These are usually removed within 36 hours while the pacing wires are generally left in place until right before the patient is discharged from the hospital.

Transcatheter therapy

At transcatheter therapy, the new artificial valve is placed on the tip of a catheter, around a balloon. When the catheter reaches the anatomical position of the aortic valve, the balloon is inflated, the new valve is anchored on the calcified aortic root. Two are the main roots for the catheter to access the arterial system is through the femoral artery (transfemoral root) or through the apex of the heart (transapical approach). Fluoroscopy and TTE are utilisted for the positioning of the valve.

Outcomes

Symptoms of the aortic disease that led the patient to the operating room, are usually relieved after the surgery. The survival curve of patients that undergo aortic valve replacements is slightly inferior of the curve of their corresponding healthy same-aged same sex population. (Pre-operative) Severe left ventricular hypertrophy was identified as a contributing factor to morbidity.

The risk of death or serious complications from aortic valve replacement is typically quoted as being between 2-5%, depending on the health and age of the patient. Older patients, as well as those who are frail and/or have multiple comorbidities (i.e. other health problems), may face significantly higher surgical risk. Common causes for adverse early outcomes are cardiac infraction/failure, arrhythmia or heart block (typically requires the permanent insertion of a cardiac pacemaker), mediastinal bleeding, stroke or infection. Late complications are endocarditis, thromboembolic event, prosthetic valve dysfunction and paravalvural leak.

The Society of Thoracic Surgeons in the USA, cites the mortality rate of isolated AVR at 2,6%. If AVR is combined with Coronary Artery Bypass, the mortality rises to 6,8%.

Patient-Prosthesis mismatch

When dealing with a small aortic annulus, the surgeon might be forced to insert a small prosthetic aortic valve, with an orifice less of what the body of the patient needs. Various techniques or stentless valves have been utilised in order to avoid this phenomenon.

Hospital stay and recovery time

After aortic valve replacement, the patient will frequently stay in an intensive care unit for 12–36 hours. The patient is often able to go home after this, in about four to seven days, unless complications arise.

Recovery from aortic valve replacement will take about three months, if the patient is in good health. Patients are advised not to lift anything heavier than 10 lbs for several weeks, and not to do any heavy lifting for 4–6 months after surgery to avoid damage to the sternum (the breast bone). Often patients will be referred to participate in Cardiopulmonary rehabilitation, which deals with optimizing recovery and physical function in patients with recent cardiac surgeries. This is often done in an outpatient setting.

Less invasive procedures

More recently, some cardiac surgeons have been performing aortic valve replacement procedures using an approach referred to as minimally invasive cardiac surgery (MICS), in which the surgeon replaces the valve through small incisions between two and four inches in length using specialized surgical instruments rather than by cutting a six to ten-inch incision down the center of the sternum. Other minimally invasive techniques include transapical approach to the aortic valve or approaching the valve through a groin incision.

Another promising alternative for many high risk and older patients is transcatheter aortic valve replacement (TAVR, also known as TAVI, transcatheter aortic valve implantation), which delivers a new valve to the site of the diseased valve through a catheter, without removing the diseased valve.The replacement valve is collapsed and packaged in a way similar to a stent. Once in place it is expanded, pushing the old valve’s leaflets out of the way, and functions in place of the old valve. The catheter may be inserted through the femoral artery or through a small incision in the chest and then through a large artery or the tip of the left ventricle. TAVR is suggested for patients with severe Aortic Stenosis who are at high risk for surgical Aortic Valve Replacement because of comorbidities or advanced age.

Robotic aortic valve replacement has been performed by a Surgeon in 2010 but its use has not spread.

See also

• Aortic valve repair
• Artificial heart valve
• Valvular heart disease
• Minimally invasive cardiac surgery
• Pericardial heart valves
• Open aortic surgery

Sources

• Brzezinski, Anna (28 August 2017). "Pathophysiology of Aortic Valve Disease". In Lawrence H. Cohn; David H. Adams (eds.). Cardiac Surgery in the Adult Fifth Edition. McGraw-Hill Education. ISBN 978-0-07-184487-1. {{cite book}}: Invalid |ref=harv (help)
• Emery, Robert W. (28 August 2017). "Aortic Valve Replacement with a Mechanical Cardiac Valve Prosthesis". In Lawrence H. Cohn; David H. Adams (eds.). Cardiac Surgery in the Adult Fifth Edition. McGraw-Hill Education. ISBN 978-0-07-184487-1. {{cite book}}: Invalid |ref=harv (help)
• Fullerton, David A (2014). "Aortic Valve Replacement". In Larry Kaiser; Irving L. Kron; Thomas L. Spray (eds.). Mastery of Cardiothoracic Surgery. Lippincott Williams & Wilkins. ISBN 978-1-4511-1315-0. {{cite book}}: Invalid |ref=harv (help)
• Gao, Changqing (2014). Robotic Cardiac Surgery. Springer Netherlands. ISBN 978-94-007-7659-3. {{cite book}}: Invalid |ref=harv (help)
• Kouchoukos, Nicholas T. (27 September 2012). Kirklin/Barratt-Boyes Cardiac Surgery E-Book. Elsevier Health Sciences. ISBN 1-4557-4605-3. {{cite book}}: Invalid |ref=harv (help)
• Pibarot, Philippe; Dumesnil, Jean G. (2009-02-24). "Prosthetic Heart Valves". Circulation. 119 (7). Ovid Technologies (Wolters Kluwer Health): 1034–1048. doi:10.1161/circulationaha.108.778886. ISSN 0009-7322. {{cite journal}}: Invalid |ref=harv (help)
• Sabiston (16 December 2010). Sabiston and Spencer's Surgery of the Chest E-Book. Elsevier Health Sciences. ISBN 1-4557-0009-6. {{cite book}}: Invalid |ref=harv (help)
• Yanagawa, Bobby (28 August 2017). "Stented Bioprosthetic Aortic Valve Replacement". In Lawrence H. Cohn; David H. Adams (eds.). Cardiac Surgery in the Adult Fifth Edition. McGraw-Hill Education. ISBN 978-0-07-184487-1. {{cite book}}: Invalid |ref=harv (help)

External links

• Information on Aortic Valve Replacement
• Animation of Aortic Valve Replacement