Aortic valve replacement

Definition

Aortic valve replacement is the insertion of a mechanical or tissue valve in place of the diseased biological aortic valve.

Purpose

Aortic valve replacement is necessary when the aortic valve has become diseased. The aortic valve can suffer from insufficiency (inability to perform adequately) or stenosis (narrowing). An insufficient valve is leaky and allows blood to flow backward from the aorta to the left ventricle during diastole, which occurs when the ventricles fill with blood.


A stenotic valve prevents the forward-moving flow of blood from the left ventricle to the aorta, during systole, which is the time period when the heart is contracting.

Either situation can result in heart failure and an enlarged left ventricle. With aortic stenosis, the symptoms of angina pectoris, fainting, and congestive heart failure will develop with the severity of the narrowing. There is an increased rate of sudden death of patients with aortic stenosis. Dyspnea (labored breathing), fatigue, and palpitations are late symptoms of aortic insufficiency. Angina pectoris is associated with the latest stages of aortic insufficiency.


Demographics

Congenital birth defects involving a bicuspid aortic valve can develop stenosis. These patients may become symptomatic in mid-teen years through age 65. Patients with a history of rheumatic fever have a disposition for aortic stenosis, but may live symptom free for more than four decades. Calcification of the aortic valve tends to effect an older population with 30% of patients over age 85 having stenosis at autopsy.

Patients with aortic stenosis who have angina, dyspnea, or fainting are candidates for aortic valve replacement. Asymptomatic patients undergoing coronary artery bypass grafting should be treated with aortic valve replacement, but otherwise are not candidates for preventive aortic valve replacement.

Patients with a history of rheumatic fever or syphilitic aortitis (inflammation of the aorta) face the possibility of developing aortic insufficiency. Successful treatment has decreased this causative relationship. Primary causes of aortic valve disease include bacterial endocarditis, trauma, aortic dissection, and congenital diseases.

Patients showing acute symptoms, including pulmonary edema, heart rhythm problems, or circulatory collapse, are candidates for aortic valve replacement. Chronic pathologies are recommended for surgery when patients appear symptomatic, demonstrating angina and dyspnea. Asymptomatic patients also must be monitored for heart dysfunction. Left ventricular dimensions greater than 2 in (50 mm) at diastole or 3 in (70 mm) at systole are indications for replacement when aortic insufficiency is diagnosed.



Description

While receiving general anesthesia in preparation for the surgery, the patient's cardiac function will be monitored. A sternotomy (incision into the sternum) or thoracotomy may be used to expose the heart, with the thoracotomy providing a smaller incision through the ribs. Minimally invasive techniques may also be used, utilizing a partial sternotomy or a lateral minithoracotomy. These approaches seem to decrease patient recovery time, as well as decreasing potential complications. Anticoagulant is administered in preparation for cardiopulmonary bypass. Cardiopulmonary bypass is instituted by exposing and cannulating (putting tubes into) the great blood vessels of the heart, or by cannulating the femoral artery and vein. A combination of cannulation sites may also be used. The heart is stopped after the aorta is clamped. The base of the aorta root is opened, and the diseased valve is removed. Sutures are placed in the aortic rim and into the replacement valve. The replacement valve can be either mechanical or biological tissue. The replacement valve will be sized prior to implant to ensure that it fits the patient based on the size of the aortic valve annulus. Once seated, the valve is secured by tying the individual sutures. The heart is then deaired. The cross clamp is removed and the heart is allowed to beat as deairing continues by manipulation of the left ventricle. Cardiopulmonary bypass is terminated, the tubes are removed, and drugs to reverse anticoagulation are administered.

A heart valve prevents the flow of blood backward during heartbeats. Replacement heart valves can be mechanical or biological tissue valves. For patients younger than 65 years of age, the mechanical valve offers superior longevity. Anticoagulant medication is required for the life of the patient implanted with a mechanical valve. The biological tissue valve does not require anticoagulation but suffers from deterioration, leading to reoperation, particularly in those under age 50. Women considering bearing children should be treated with biological tissue valves because the anticoagulant of choice with mechanical valves, warfarin, is associated with developmental effects in the fetus. Aspirin can be substituted in certain circumstances.

Diagnosis/Preparation

Initial diagnosis by auscultation (listening) is done with a stethoscope. Additional procedures associated with diagnosis to judge severity of the lesion include chest x ray, echocardiography, and angiography with cardiac catheterization. In the absence of angiography, magnetic resonance imaging (MRI) or computed tomographic (CT) imaging may be used.

Aftercare

The patient will have continuous cardiac monitoring performed in the intensive care unit (ICU) postoperatively. Medications or mechanical circulatory assist may be instituted during the surgery or postoperatively to help the heart provide the necessary cardiac output to sustain the pulmonary and systemic circulations. These will be discontinued as cardiac function improves. As the patient is able to breathe without assistance, ventilatory support will be discontinued. Drainage tubes allow blood to be collected from the chest cavity during healing and are removed as blood flow decreases. Prophylactic antibiotics are given. Anticoagulation (warfarin, aspirin, or a combination) therapy is instituted and continued for patients who have received a mechanical valve. The ICU stay is approximately three days with a final hospital discharge occurring within a week after the procedure.

The patient receive wound care instructions prior to leaving the hospital. The instructions include how to recognize such adverse conditions as infection or valve malfunction, contact information for the surgeon, and guidelines on when to return to the emergency room.

Risks

There are unassociated risks with general anesthetic and cardiopulmonary bypass. Risks associated with aortic valve replacement include embolism, bleeding, and operative valvular endocarditis. Hemolysis is associated with certain types of mechanical valves, but is not a contraindication for implantation.

Normal results

Myocardial function typically improves rapidly, with decrease in left ventricle enlargement and size of the inner chamber over several months, allowing the heart to return to normal dimensions. Anticoagulation therapy will be continued, depending on the type of mechanical valve implanted. Implantation of biological tissue valves are associated with the formation of blood clots. If non-cardiac surgery or dental care is needed, the anticoagulant medication will be adjusted to prevent bleeding complications.

Morbidity and mortality rates

There is a 3-5% hospital mortality associated with aortic valve replacement. The average survival rate after five years is 85% for patients suffering from aortic stenosis who undergo aortic valve replacement. Structural valve deterioration can occur and is higher in mechanical valves during the first five years; however, biological tissue and mechanical valves have the same failure incidence at 10 years, with a 60% probability of death at 11 years as a result of valverelated complications. Patients with a mechanical valve are more likely to experience bleeding complications. Reoperation is more likely for patients treated with a biological tissue valve, but not significantly different when compared to their mechanical valve counterparts. This combines to an average rate of significant complications of 2-3% per year, with death rate of approximately 1% per year associated directly with the prosthesis.


Alternatives

Balloon valvotomy may provide short-term relief of aortic stenosis, but is considered a temporary treatment until valve replacement can be accomplished. Aortic valve repair by direct commissurotomy may also be successful for some cases of aortic stenosis. Medical treatment for inoperable patients with severe aortic stenosis is used to relieve pulmonary congestion and prevent atrial fibrillation.

Severe aortic insufficiency can be treated with medical therapy. Pharmaceuticals to decrease blood pressure, along with diuretics and vasodilators, are helpful in patients with aortic insufficiency.