Aortic valve replacement
Aortic valve replacement is the insertion of a mechanical or tissue valve in place of the diseased native aortic valve.
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. An insufficient valve is leaky and allows blood flow retrograde from the aorta to the left ventricle during diastole. A stenotic valve prevents the flow of blood antegrade from the left ventricle to the aorta, during systole.
Either situation can result in heart failure and an enlarged left ventricle. With aortic stenosis (narrowing), 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.
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 rheumatic fever have a disposition for aortic stenosis, but may live symptom free for more then 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 disease commonly 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 must be monitored for heart dysfunction. Left ventricular dimensions greater then 2 in (50 mm) at diastole or 3 in (70 mm) at systole are indications for replacement when aortic insufficiency is diagnosed.
While receiving general anesthesia in preparation for the surgery, the patient's cardiac function will be monitored. A sternotomy (incision in the sternum) or thoracotomy may be used to expose the heart, with the thoracotomy providing a smaller incision through the ribs. Anticoagulant is administered in preparation for cardiopulmonary bypass. Cardiopulmonary bypass is instituted by exposing and cannulating (putting tubes in) 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 aortic 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 is an orifice that blood passes through in systole, and it is also an occluding (blocking) mechanism necessary to prevent the flow of blood during diastole. Heart valves can be mechanical or biological tissue valves. For patients younger then 65 years of age, the mechanical valve offers superior longevity. Anticoagulation 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 as the anticoagulant of choice with mechanical valves, warfarin, is associated with teterogenic effects in the fetus. Aspirin can be substituted in certain circumstances.
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.
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. Prophylaxis 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.
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.
Myocardial function typically improves rapidly, with decrease in left ventricle enlargement and dilation over several months, allowing the heart to return to normal dimensions. Anticoagulation therapy will be continued to elevate the INR to between 2.0 and 4.5, depending on the type of mechanical valve implanted. Implantation of biological tissue valves with maintenance of an INR of 2.0–3.0 for the initial three months post implant are associated with blood clot complications. If non-cardiac surgery or dental care is needed the antithrombotic therapy will be adjusted to prevent bleeding complications.
Morbidity and mortality rates
There is a 3–5% hospital mortality associated with aortic valve replacement. There is an average survival rate of five years in 85% of patients suffering from aortic stenosis that 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 a valve-related 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.
Balloon valvotomy may provide short term relief of aortic stenosis, but is considered palliative until valve replacement can be accomplished. Aortic valve repair by direct commisurotimy may also be successful for some cases of aortic stenosis. Medical treatment for inoperable patients with severe aortic stenosis is used to relive pulmonary congestion and prevent atrial fibrillation.
Severe aortic insufficiency can be treated with medical therapy. Pharmaceuticals to decrease blood pressure, with diuretics and vasodilators, are helpful in patients with aortic insufficiency.
Hensley, Frederick A., Donald E. Martin, and Glenn P. Gravlee, eds. A Practical Approach to Cardiac Anesthesia. 3rd Edition. Philadelphia: Lippincott Williams & Wilkins Philadelphia, 2003.
Bonow R, et al. "ACC/AHA Guidelines for the Management of Patients with Valvular Heart Disease." JACC 32 (November 1998): 1486–588.
Allison Joan Spiwak, MSBME
WHO PERFORMS THE PROCEDURE AND WHERE IS IT PERFORMED?
Hospitals with cardiac surgery services provide aortic valve replacement. Specialization is required for young adults and pediatric patients. Cardiovascular and cardiac surgeons are trained to provide this treatment and the initial follow-up care. These surgeons are trained in their cardiac surgical residency to evaluate and perform these procedures and to care for the patient during the post-operative period.
QUESTIONS TO ASK THE DOCTOR
- What type of valve is best suited for me?
- What are the pros and cons associated with each type of valve for a person with my disease and/or associated diseases?
- Why am I a candidate for valve replacement?
- Are there any other more suitable alternative procedures?
- If I am a female interested in having children, or currently pregnant are there additional options?
- How often has the surgeon performed this procedure and what are the morbidity/mortality statistics for this surgeon and institution?
- If I have an associated disease or complicated scenario does the surgeon have experience with follow-up care?