Continuing Education Activity

Aortic valve replacement is indicated when aortic stenosis or regurgitation disturbs the flow of blood out of the heart. Homograft valve and pulmonary autograft valve are two commonly used bioprosthetic grafts for aortic valve replacement. Main indications for aortic valve replacement are symptomatic aortic stenosis or regurgitation. This activity reviews the evaluation and treatment of aortic valve disease and highlights the role of the interprofessional team in evaluating and treating this condition.

Objectives:

• Identify the indications for aortic valve replacement, stentless, autograft/homograft.
• Describe the preparation, and technique of aortic valve replacement, stentless, autograft/homograft.
• Review the potential complications of aortic valve replacement, stentless, autograft/homograft.
• Outline interprofessional team strategies for improving care coordination and communication to advance aortic valve replacement, stentless, autograft/homograft, and improve outcomes.

Introduction

A valve is a mobile, thin sheet of tissue present in a pathway, and maintains a unidirectional flow through the passage. The heart valves become insufficient, or they get stenosed. Patients with damaged aortic valves are managed with medicines, aortic valve repair, surgical or transcatheter aortic valve replacement.[1][2] Prosthetic heart valves used for replacement of damaged aortic valves are of two types, mechanical and bioprosthetic. Three common types of mechanical heart valves are disc valves, bi-leaflet valves, and ball and cage valves. Bioprosthetic valves are further divided into xenografts (from animals), homografts (from the same species), and autografts (from the same individual). Bioprosthetic valves can be stented on metallic support or can be attached directly to the aorta.[3]

Stent placement reduces the lumen of the aortic valve and is not favorable hemodynamically, but there is no difference in the clinical outcomes of two types of valves.[4] The selection of prosthetic valves depends upon the patient's choice, age, anticoagulation tolerance, risk of valve deterioration, anticoagulation status, future pregnancy plans, etc.[5] Different types of bioprosthetic valves have similar mortality and reoperation outcomes.[6] Transcatheter aortic valve replacement is a comparatively safer option for patients who cannot undergo an open-heart valve replacement procedure.

Anatomy and Physiology

The aortic valve consists of three cusps that prevent the backflow of blood from the aorta to the left ventricle. Mostly the three cusps have different sizes.[7] Aortic valve insufficiency or stenosis leads to turbulence in the flow of blood and are identified by murmurs. Aortic stenosis leads to a crescendo-decrescendo systolic murmur in the right second intercostal space that radiates to the carotids. Calcification of the aortic valves in old age, chronic rheumatic heart disease, and congenital bicuspid aortic valves are common causes of aortic stenosis.

Aortic stenosis can present with shortness of breath, chest pain, fatigue, dizziness, etc. Aortic regurgitation leads to a diastolic blowing type murmur in the third intercostal space on the left side along the sternal border. Aortic valve calcification, bicuspid valve, rheumatic heart disease, and root dilatation are common causes of regurgitation. Palpitations and shortness of breath are common symptoms of aortic regurgitation.[8] Any damage to the heart valves put them at risk for endocarditis. Characteristic features of endocarditis are fever, pulmonary infarcts, arterial emboli, Janeway lesions, splinter hemorrhages, conjunctival hemorrhages, painful Osler nodes, Roth spots, glomerulonephritis, new-onset heart murmur, and positive blood cultures. Duke criteria are used to assess the probability of endocarditis.[9]

In the Ross procedure, the pulmonary valve of the patient is used to replace the defected aortic valve. The pulmonic valve is replaced with a bovine jugular vein conduit in patients less than six years. Decellular pulmonary homograft is preferred for older patients.[10] Homografts are obtained from cadaveric or brain dead heart donors. The heart valve, along with peri-annular tissue from a donor, is used to replace the valve and close the defect in the peri-annular tissue. Route of coronary arteries, along with their branches, are kept in mind while doing the valve replacement procedure.[11]

Indications

Aortic stenosis is managed symptomatically with beta-blockers (atenolol, nebivolol, etc.), calcium channel blockers (verapamil, diltiazem), or diuretics (furosemide, thiazides, angiotensin-converting enzyme (ACE) inhibitors, etc.). The following are commonly used indications for aortic valve replacement.

• Patients with stage D1 aortic stenosis (symptomatic high grade).
• Patients with stage C2 aortic stenosis (aymptomatic high grade) with < 50% left ventricular ejection fraction.
• Patients with stage C1 aortic stenosis (asymptomatic severe) with low exercise tolerance.
• Patients with stage C1 aortic stenosis (asymptomatic severe) and aortic velocity > 4.5 m/s with low surgical risk.
• Patients with stage C or D aortic stenosis undergoing any other cardiac surgery.[12]

Similarly, for aortic regurgitation, diuretics, and vasodilators (nifedipine, ACE inhibitors, etc.) are used for symptomatic management, the following are common indications for valve replacement, 

• Patients with stage D aortic regurgitation (symptomatic severe).
• Patients with stage C2 aortic regurgitation (asymptomatic severe) with < 50% ejection fraction or > 50 mm end-systolic dimension or > 65mm end-diastolic diameter.
• Patients with stage B, C, or D undergoing any other cardiac surgery.[2]

There is insufficient data to indicate a specific type of prosthesis for aortic valve replacement. But the following points favor a bioprosthetic heart valve.

• Contraindications, non-compliance, or refractory to anticoagulant drugs.
• Fully informed patients' desire.
• Patients with mechanical valve thrombosis.
• Low risk of valve redo-operations.
• Future pregnancy plans.
• Age of more than 65 years.[5]

Autograft aortic valve replacement is done with the Ross procedure. This technique is preferred in children, and young adults as pulmonic valves used as graft have the potential to grow and regenerate and have a lower risk for endocarditis.[10] Homografts are preferred in case of aortic valve endocarditis, especially in case of peri-annular abscess as peri-annular graft tissue can also be used to path these defects. Homografts are also preferred in patients with a history of intravenous (IV) drug abuse and resultant endocarditis as they have a higher risk of reoperations.[11] Xenografts are readily available in all sizes.[13]

Contraindications

Common contraindications for Ross procedure are connective tissue diseases (Marfan disease, Ehlers-Danlos syndrome, etc.) and inflammatory disorders. Inflammatory disorders commonly include rheumatoid arthritis, systemic lupus erythematosus, etc. These diseases frequently involve pulmonary aorta or pulmonary valve. Other contraindications are multiple vessel coronary artery disease, a severe decrease in left ventricular function, or any pulmonary valve pathology. There are no specific contraindications for aortic valve homografts depending upon the availability of donor, and preference of the surgeon and the patient. Young age is considered a relative contraindication for homograft valve replacement.[13][14]

Equipment

Aortic heart valve replacement is done via open median sternotomy. Heart valves are first assessed with echocardiography. Other types of equipment used in the procedure are Hegar dilator (to measure the autografts) and polypropylene sutures (to attach the graft valve). Dacron tube is used in the Ross procedure to extend the pulmonary valve.[15][16]

Personnel

A team consisting of an anesthesiologist, cardiac surgeon, cardiologist, surgery assistants, operation room assistant, a radiologist, and additional staff members is required to perform an aortic heart valve replacement surgery.[17]

Preparation

The main goal of preparation is sterility. Before starting the procedure, the whole chest is shaved and sterilized. The patient is draped based on the institution protocols, and other general anesthesia-related preparations are done. Important landmarks (like jugulum, xiphoid process) are identified and marked before starting the procedure.[17][18]

Technique or Treatment

Aortic valve replacement by Ross procedure is done with median sternotomy and bicaval and aortic cannulation. Cardioplegia is obtained mostly with cold intermittence. Warm reperfusion is done before the aortic clamp is released. Common adventitia between pulmonary root and aorta is dissected to reach muscular infundibulum. Both the aortic and pulmonary valves are inspected first before any extraction. The pulmonary valve is extracted while making sure that the valve is in good shape, and the first septal coronary artery is preserved. The Hegar dilated is then used for the measurement of autograft. The next step is the removal of the diseased valve. The annulus is then measured to match it with the graft. Annuloplasty is done in case of any mismatch. Valve leaflets are then attached to the aorta with the help of polypropylene sutures. After the autograft implantation, the left coronary button is anastomosed first, others later. Then the surgeon performs distal anastomosis of pulmonary graft first and distal anastomosis of aortic graft later. The final part is to secure the proximal portion of the pulmonary graft with a running suture.[16][19]

Homograft aortic valve replacement is also done with a median sternotomy followed by cardioplegia. During the procedure, the surgeon makes sure to remove all the infected tissue along with a damaged aortic valve. Debridement procedure may lead to mitro-aortic junction defect. Anterior mitral leaflet or a part of a leaflet from the graft is used to fil this defect. Then the atrium is sutured along with a pericardial patch if needed.[15]

Complications

About 30% of patients face pulmonary autograft dilatation after the Ross procedure. After the Ross procedure, patients with age < 25years almost always require autograft reintervention at some time in life. For older patients, there is a risk of 32% to 68% for reintervention due to graft valve-related complications. Younger age is also associated with right ventricular outflow tract conduit degeneration. Ross procedure is associated with a comparatively lower number of bleeding, thrombosis, and endocarditis related complications as compared to other types of graft replacements. Lesser number of early and late mortality is associated with this procedure.[20][21]

Homograft aortic valve replacement may lead to early mortality, but the incidence is low. Structural deterioration of graft may occur in about 20 years due to the rupture of graft leaflet, calcification of graft valve, or poor coaptation of leaflets. Early reinfection rate is low, but late infections may occur in 4 months to 5 years. Valve deterioration and reinfections may lead to reinterventions.[22]

Clinical Significance

Ross procedure was first described in 1947. It has the advantage that surgeons use viable autograft that can grow, regenerate, and has a low risk of endocarditis. These characteristics make them ideal for pediatric and young patients. Pediatric Ross procedure has lower mortality and a lower rate of reinterventions as compared to other graft procedures.[10] Homograft aortic valve replacement is a complex procedure but has good clinical outcomes in adults and patients with future pregnancy plans.[23]

Enhancing Healthcare Team Outcomes

The aortic valve replacement procedure is major cardiac surgery. There should not be any communication gap between the team members. A thorough assessment of the patient before, during, and after the procedure leads to better outcomes. Negligence can lead to preventable adverse events. Appropriate care provides better results after heart valve replacement. Phase 2 randomized clinical trial has shown better VO2 max (maximum oxygen utilized during exercise) in patients with cardiac rehabilitation.[24] [Level 2]