With the heart-lung machine, which allows the heart to be transiently bypassed while the surgeon works on the heart, open-heart surgery has become practical and has allowed the correction or replacement of defective or diseased heart valves.

Anatomy

• The heart is a muscular organ about the size of a clenched fist. It lies in the chest beneath the sternum or breast bone
• The function of the heart is to supply blood to the body. The heart is divided into four chambers, two upper chambers called the right and left atria and two lower chambers called the right and left ventricles (Figure 1)

Figure 1- Anatomy of the heart and heart valves. The black arrows indicate the direction of blood flow through each valve. © N. Gordon

• The valves control the direction of flow of blood through the heart
• The left ventricle of the heart pumps blood through the aortic valve into the aorta, the largest artery of the body, and then through a network of arteries to the whole body, After passing through the tissues of the body, the blood collects into the veins and returns to the right atrium
• From the right atrium, blood than passes through the tricuspid valve into the right ventricle
• The right ventricle pumps the blood through the pulmonary valve into the arteries of the lungs where the blood picks up oxygen and gives up carbon dioxide
• The oxygenated blood returns to the left atrium after which it passes through the mitral valve to the left ventricle and the cycle repeats
• The aortic and pulmonary valves are tri-leaflet (have three leaflets or cusps) and similar in design. They are attached to a fibrous ring imbedded in the cardiac tissues
• The mitral valve has two cusps and the tricuspid valve has three cusps and function in a parachute fashion. The cusps are anchored to the heart wall by chordae tendineae (fibrous cords) attached to papillary muscles, strong thin muscles that blend into the heart wall and function to support the valve apparatus. The edge of the valve at its attachment to the heart is called the annulus
• Like all tissues in the body, the heart requires oxygen filled blood in order to function. Blood nourishes the heart through the right and left coronary arteries. The left main coronary artery gives off two major branches, the circumflex and obtuse marginal arteries, before it continues as left anterior descending artery. The right coronary artery gives off the marginal artery before it continues as the posterior descending artery

Pathology

A valve that does not work properly can markedly impair the function of the heart.

• The etiologies (causes) of the dysfunctional valves may be
  1. congenital - exists from birth
  2. acquired - develops after birth
  3. infectious - due to infection of the valve
  4. degenerative - due to deterioration of the tissues
• They become dysfunctional when the valve becomes either stenotic (leaflets are closed down) or regurgitant (wide open leaflets). In either condition the valve may become calcified (crusted with calcium deposits) and blood flow from the pumping chamber is abnormal
• Aortic regurgitation (also called aortic insufficiency) exists when the leaflets of the aortic valve become incompetent and can no longer close adequately. The etiology of this may be due to a build up of calcium, degeneration or infection
• The same disease processes that affect the aortic and pulmonary valves can also affect the tricuspid and the mitral valves leading either to stenosis or regurgitation
• The most commonly affected valves are the aortic and the mitral
• Aortic stenosis: The etiology of acquired aortic stenosis has dramatically changed over the years. Rheumatic heart disease and bacterial infection of the inside of the heart were responsible for most cases of aortic stenosis until a few decades ago. Now most are due to calcific or degenerative changes in the valve producing thickening and the sticking together of the margins of the cusps. With progression, the opening in the valve becomes smaller and smaller
• Aortic regurgitation: This may occur due to rheumatic heart disease, syphilis, trauma and bacterial endocarditis (inflammation of the inside lining of the heart)
• Mitral stenosis: This is a condition in which a constriction of the mitral valve no longer allows blood to freely pass from the left atrium into the left ventricle causing subsequent heart failure. The cause is most commonly rheumatic in nature, however, it may also be seen with progressive degenerative calcification
• Mitral regurgitation (insufficiency): In this condition the cusps of the mitral valve can no longer close properly. This may be seen with inflammatory or rheumatic causes, but now it is more commonly degenerative
• Most frequent causes of mitral insufficiency are
  1. Myxomatous (mucous-like) degeneration of the mitral valve is associated with lengthening and rupture of the chordae tendineae and an increased risk of endocarditis
  2. Poor function of the papillary muscle due to decreased blood supply such that the muscle can no longer contract properly
  3. Functional regurgitation in which the leaflets of the valve fall to close properly
  4. Enlargement of the left ventricle causing overstretching of the mitral annulus
• Less common disorders include
  1. infectious endocarditis
  2. rheumatic heart disease
  3. calcifications of the mitral annulus
• Tricuspid Stenosis: This is usually seen with rheumatic heart disease. Calcification is not usually seen with tricuspid stenosis. It is almost always seen along with mitral stenosis
• Tricuspid Regurgitation occurs most frequently as a result of heart dilatation and failure. Rheumatic fever and bacterial endocarditis (frequently as the result of intravenous drug abuse)
• Pulmonary Stenosis: This is a congenital (seen at birth) heart defect

History and Examination

• Aortic Stenosis:
  1. Aortic stenosis has become a disease of the elderly
  2. The classic finding is a short, harsh murmur (abnormal heart sound)
  3. There is generally a lengthy period from initial discovery of a murmur and the first onset of symptoms at which time there is a fairly rapid downhill course. Once symptoms develop the outcome of patients with aortic stenosis is quite poor. Early studies predicted a mortality of 50% at five years
  4. Earliest symptoms are easy fatigue and difficulty in breathing with any kind of exertion
  5. As the stenosis progresses, the patient may develop congestion of the lungs and occasionally edema (fluid in the tissues) in the legs
  6. With severe stenosis, symptoms of a decrease in blood to the brain such as faintness, dizziness, or syncope (passing out) may occur and these patients may be subject to sudden death
  7. Calcification of the valve may be seen on X-ray
  8. Left ventricular failure patients are most likely to have critical outflow obstruction from the heart. Catheterization of the left side of the heart (see cardiac catheterization) allows direct measurement of the loss of pressure across the aortic valve
• Aortic Regurgitation
  1. The characteristic murmur is a soft high pitched sound that is heard near the left border of the breast bone
  2. The left ventricle of the heart is enlarged on examination
  3. The diastolic blood pressure (the lower number) is lowered resulting in a wide pulse pressure (difference between the systolic, upper number, and the diastolic pressure) - the water hammer pulse 4. A pistol-shot sound heard over the artery to the leg in the groin
• Mitral Stenosis
  1. There is usually a history of gradually increasing difficulty
  2. By the time a patient feels tired and short of breath, the mitral stenosis has already become severe
  3. There is shortness of breath at night or with any exertion
  4. There may be rupture of the lung capillaries with coughing up of blood
  5. The most common murmur is coarse, rumbling and low pitched heard near the lower part of the heart
  6. Chest X-ray shows enlargement of the left atrium and right ventricle along with dilatation of the pulmonary (lung) arteries
  7. Calcification of the valve may be seen on X-ray
  8. The electrocardiogram (EKG, tracing of the electrical activity of the heart) may be normal or may show an irregular heartbeat and evidence of enlargement of the right ventricle
  9. Catheterization of the heart allows direct measurement of the increased right ventricular and left auricular pressure
• Mitral Insufficiency
  1. With mitral insufficiency there can be a vicious cycle produced. To compensate the insufficiency, the ventricle dilates, which stretches the annulus and causes more insufficiency
  2. The patient may complain of shortness of breath and fatigue
  3. The characteristic 'blowing' murmur is heard near the apex (tip of the left ventricle) of the heart
  4. The enlarged left ventricle can at times be felt over the chest
  5. Chest X-ray shows a large heart
  6. There are changes on the EKG
• Tricuspid Stenosis
  1. The diagnosis may be difficult because the effects of the usually associated mitral stenosis overshadow those of the tricuspid stenosis
  2. Because blood entering the heart backs up at the stenotic tricuspid valve, there may be distention of the veins in the liver resulting in ascites (the seepage of fluid into the abdomen)
• Tricuspid Insufficiency
  1. The characteristic murmur is heard at the lower of the breastbone
  2. Large right side if the heart seen on X-ray
  3. Pulsatile veins in the neck (veins expand with each heart pulse)
  4. Able to feel a pulsatile liver
• Pulmonary Stenosis
  1. This is found in infants
  2. The infant may be cyanotic (bluish discoloration of the skin)
  3. There is a harsh murmur heard over the upper part of the heart
  4. X-ray shows an enlarged right ventricle
  5. Cardiac catheterization shows a characteristic difference between the right ventricle and pulmonary artery

Special Diagnostic Tests

• X-ray of the chest may show an enlarged heart
• Electrocardiogram (EKG) may show an abnormal tracing
• Echocardiography- Sound waves are sent out from the transducer (part of the apparatus that sends and receives the sound waves), reflected off of the heart and returned to the transducer. A 'sound' picture of the heart is then created on the monitor (Figure 2A, 2B)
  1. transthoracic - through the chest wall
  2. transesophageal - through the esophagus
• Treadmill testing with and without the use of low level radioactive isotopes
• Cardiac catheterization- A catheter is placed into the right heart from the femoral vein or left heart from the femoral artery in the groin. Pressure measurements are taken from in the various chambers of the heart. A special dye visible on X-ray is also injected to outline the heart abnormalities

Figure 2a - Ultrasound picture of aortic valve regurgitation. Note that there is a flow of blood (in red) back into the left ventricle. Courtesy S. Sadiq, MD	Figure 2b - Ultrasound picture of a stenotic aortic valve due to calcification of the valve. Courtesy S. Sadiq, MD

Indications for surgery

• Aortic stenosis: Current thoughts on the management of aortic stenosis would dictate an earlier intervention to improve mortality figures. In the patient with totally asymptomatic mild aortic stenosis the valve replacement should be deferred. In those patients with minimal to moderate symptoms consideration should be given to aortic valve replacement
• Aortic regurgitation: Patients with aortic regurgitation that have symptoms should have the valve replaced
• Mitral stenosis: Most patients with mitral stenosis will develop symptoms indicating progressive failure of the heart. These patients should have surgery as soon as the problem is determined
• Mitral insufficiency: Patients with no or only mild symptoms may be treated with medication and watched. Once the patient starts developing more severe symptoms, surgery is indicated
• Tricuspid stenosis: Although rare, tricuspid stenosis should be corrected when symptoms are present
• Tricuspid insufficiency: This problem is usually associated with other valve problems such as mitral stenosis or regurgitation or aortic stenosis or regurgitation. Once the patient develops symptoms, tricuspid insufficiency should be corrected
• Pulmonary stenosis: Although rare, pulmonary stenosis with symptoms should be corrected when found

Surgical Procedures

• The operation takes approximately three to six hours depending on its complexity. The anesthesiology team first inserts intravenous lines and lines for monitoring. General anesthesia is administered so the patient will be completely pain free during the procedure
• An incision along the midline of the chest through the breast bone is used
• During the operation a heart-lung machine (cardiopulmonary bypass machine) is used to mix the patient's blood with oxygen and nutrients outside the body and return it to the patient's circulation through tubes going into the large vein
• The current surgical therapy for most diseased valves is replacement of the valve with either a bioprosthetic device or a mechanical device
  1. Bioprosthetic devices are valves from other animals - porcine (pig) valve with or without a supporting stent, bovine (cow) pericardial valve, and homograph (human) valve. Bioprosthetic devices often require only a short time of anticoagulation, but do not last as long and, therefore, are usually used in an older patient
  2. Most mechanical valves are bileaflet in nature and function on a hinge type mechanism. These valves require lifelong anticoagulation (blood thinning) but last a long time and are thus usually used in the younger patient
• Aortic valve- the surgery for aortic stenosis usually is the replacement of the diseased valve with either a bioprosthetic or mechanical valve. Only occasionally is the valve directly repaired. In general, aortic valve repair has been only moderately successful (Figure 3)

Figure 3a - Aortic bioprosthesis A. After the patient is placed on the heart-lung machine and the aorta clamped, the aorta is partially cut across to gain access to the aortic valve. The abnormal valve is then cut out with scissors. © N. Gordon	Figure 3b - The pig aortic valve in a holder is sutured to the annulus after the aortic valve has been removed. © N. Gordon

Figure 3c - Operative photograph of pig valve sutured in place. (H-L, heart-lung machine). Courtesy W. Gordon, MD	Figure 3d - Close-up photograph of pig valve in place. Courtesy W. Gordon, MD

• Mitral valve- in comparison to aortic valve disease, reparative procedures and techniques utilized with the mitral valve have been extremely popular and successful over the past 10-20 years. When the mitral valve cannot be repaired, the options of a mechanical or bioprosthetic valve becomes necessary (Figures 4 and 5)

Figure 4a - Two methods of correcting mitral insufficiency due to stretching of the annulus	Figure 4b - A cloth ring is sutured to the annulus to restore it to the proper size. © N. Gordon

Figure 4c - A quadrangular (four angled) section of tissue is removed from the annulus. © N. Gordon	Figure 4d - The annulus is then sutured thus reducing the size of the stretched annulus. © N. Gordon

Figure 5a - Mitral bioprosthesis After the patient is placed on the heart-lung machine, the left auricle is opened to expose the mitral valve. The diseased mitral valve is cut out. © N. Gordon	Figure 5b - The pig valve held in a holder is sutured to the mitral annulus. Note the small pieces of cloth that reinforce the annulus so that the sutures do not tear through. © N. Gordon

Figure 5c - Operative photograph of a mitral pig bioprosthesis in place. Courtesy W. Gordon, MD

• Tricuspid valve- the tricuspid valve is less involved than the mitral or the aortic valve. The solution for significant tricuspid regurgitation falls into either repair or replacement with a bioprosthetic or mechanical device
• Pulmonary valve- the pulmonary valve is the least affected of the four heart valves
• Minimally invasive techniques- another form of treatment occasionally used in stenotic valve disease is a minimally-invasive technique using a catheter placed in the femoral artery in the groin and passed up through the aorta. A special balloon attached to the catheter is then expanded to correct such lesions as aortic stenosis and mitral stenosis in certain select patients. This procedure is carried out with the combined cooperation of an interventional cardiologist and cardiac surgeon to provide optimal results. The aortic valve balloon dilatation has had less success than the mitral valve balloon dilatation
• An infected valve is treated in much the same way as an non-infected valve with the exception that an attempt is made to initially sterilize the infected valve with antibiotics and to remove the cause of the infection. If sterilization can be accomplished without deterioration of heart function and the valve has returned to normal function, then the patient may be monitored closely. If the patient does not return to normal cardiac function and remains with symptoms, it may be necessary to replace the infected valve. Particularly with infections of the aortic valve, a homograph bioprosthesis has been a successful and recently recommended as the solution to this problem. In the mitral valve, homographs are being developed for selected cases

Complications

• As with any surgery, complications of heart valve surgery exist and include
• Wound infection
• Postoperative bleeding can be life threatening and may result in a return to the operating room
• Thromboembolism occurs when a clot develops in the pelvic or leg veins. The clot breaks off and travels through the veins to the right side of the heart and into the lungs where obstruction of a pulmonary artery may lead to death
• Stroke may occur soon after surgery or may occur years later due to a clot developing on the new valve
• Irregular heart rhythm (arrhythmias)
• Areas of collapsed lung (atelectasis)
• Possible death

Postoperative Recovery

• Deep breathing exercises and coughing are encouraged to help speed recovery. Coughing reduces the chance of pneumonia and fever and will not disturb the incision
• Wound care is achieved by cleansing with mild soap and water. Later, lotion may be used to prevent dryness of the skin
• It is also important to maintain an appropriate weight and avoid smoking
• Weakness is a common feeling on returning home due to lack of use of big muscles. Exercise, such as walking, is a good way to regain muscle strength. Sedentary workers may have to wait four to six weeks before returning to work
• Heart rehabilitation programs are particularly helpful in getting a patient back to a normal, healthy routine. The cardiac rehabilitation program usually begins between the third and sixth week after surgery