Percutaneous Pulmonary Valve Implantation for Treating Right Ventricular Outflow Tract Dysfunction

Proprietary names: Medtronic Melody® Transcatheter Pulmonary Valve (TPV) and Ensemble® Transcatheter Valve Delivery System; Edwards Sapien® Pulmonic Transcatheter Heart Valve (THV) and RetroFlex® Transfemoral Delivery System Generic names: percutaneous pulmonary valve (PPV), percutaneous pulmonic valve, transcatheter pulmonary valve (TPV), catheter-based pulmonary valve, Bonhoeffer valve, pulmonary valve, pulmonic valve, balloon catheter, replacement heart valve, transcatheter stent-valve, transcatheter valve (TCV), transcatheter heart valve (THV)

Cardiovascular defects can result in valve narrowing or obstruction (i.e., stenosis), leakage (i.e., regurgitation), or both (i.e., mixed). A defect in the pulmonary valve or right ventricular outflow tract (RVOT), which separates the right ventricle from the pulmonary artery, is associated with several congenital disorders. Common congenital heart disorders affecting the pulmonary valve include tetralogy of Fallot, pulmonary atresia, transposition of the great arteries, and double-outlet right ventricle.1 The stenotic or regurgitant pulmonary valve can affect ventricular function and lead to shortness of breath, fatigue, light-headedness, weakness, and exercise intolerance. These conditions may also cause heart palpitations and chest pain.2 A cardiologist uses several tools to assess cardiovascular disorders, including one or more of the following:

The New York Heart Association categorizes heart failure into four classes based on the degree to which symptoms limit physical activity: asymptomatic (class I), mild (class II), moderate (class III), and severe (class IV). Patients in class III or IV have advanced heart failure.3 Poor ventricular contractility, reduced cardiac output, and ventricular arrhythmias directly relate to the high morbidity and mortality associated with advanced heart failure. Standard treatment for pulmonary valve dysfunction involves open heart surgery to maintain or enhance blood flow from the right ventricle to the lungs. During the surgical procedure, three options are available to replace failed RVOTs: a mechanical valve, a bioprosthetic valve, or a homograft. Although durable, mechanical valves in the RVOT conduit are seldom used because of the need for lifelong anticoagulation therapy to decrease the risk of thromboembolism.4 A bioprosthetic valve replacement utilizes a porcine or equine pericardial leaflet valve supported in a plastic-metal framework and can be placed directly in the RVOT or integrated into a conduit.5 Most often, cardiac surgeons use a homograft consisting of a human cadaver aortic or pulmonary valve as a valved RVOT conduit.5 Over time, a conduit can fail for several reasons: a child with RVOT dysfunction will outgrow the conduit,6 an aneurysm can form,7 or the valve can become insufficient,7 degenerate,8 or calcify.8 Bioprosthetic valves have been reported to require replacement after an average of 10 years.9 When a conduit fails, surgeons have historically performed subsequent open heart surgery to place a new valved conduit. However, every time a patient undergoes open heart surgery, the risk increases. Thus, replacing the failed conduit is typically delayed as long as possible. In the interim, the heart muscle must work harder to pump blood through the defective conduit, causing right ventricular dilation, muscle thickening, and increased right ventricular pressure.8

In the United States, approximately 1% of all infants born alive have a congenital heart defect.10 Of these, about 22% have a defect affecting the flow of blood from the right ventricle to pulmonary artery.11 Four common causes of RVOT dysfunction, along with their U.S. incidence and prevalence rates, are as follows:

The annual worldwide incidence of these disorders is as follows:17

Increased effectiveness of treatment options for children with CHD has contributed to an increasing adult population with CHD.17

This report focuses on a new, minimally invasive approach to repair failed conduits: percutaneous pulmonary valve implantation (PPVI). Purported benefits of PPVI are restored pulmonary valve conduit function (i.e., relief of stenosis and/or regurgitation) and increased pulmonary valve conduit lifespan, which delays a patient's need for the next open heart surgery.18 PPVI could potentially reduce a patient's lifetime number of open heart surgical procedures, which may also increase overall survival rates. PPVI might also help to avoid right ventricular dysfunction through earlier intervention.5 One PPVI system (Melody Transcatheter Pulmonary Valve TPV system, Medtronic, Inc., is commercially available in the United States, Europe, Canada, and several other countries. Another system, the Sapien Transcatheter Heart Valve platform (Edwards Lifesciences) is commercially available only in Europe at this time, but clinical trials are ongoing to help achieve U.S. marketing approval. The Melody system consists of a bioprosthetic valve delivered via the Medtronic Ensemble delivery system. The valve is derived from a bovine jugular vein valve and is attached to an expandable metal frame. Before delivery, the valve is mounted onto the balloon-in-balloon Ensemble delivery system (22 Fr outer diameter), which has a protective sheath that covers the valve to facilitate delivery. The delivery system is then inserted into the femoral vein and guided into the RVOT. Once the delivery system is in place in the RVOT conduit, the interventional cardiologist inflates the balloons until the valve is fully deployed inside the conduit. The interventional cardiologist then retracts the catheter and uses fluoroscopy to ensure the valve is working correctly.19 The delivery system is available in three different balloon sizes (18, 20, and 22 mm) to account for patient physiologic variability.20 The Sapien system consists of a bovine pericardial valve sutured to a stainless-steel stent and is delivered using the RetroFlex transfemoral delivery system. The Sapien system serves a patient population with larger failed conduits because the valve (23 and 26 mm) and delivery system (22 and 24 Fr) are available in larger sizes than the Melody system.21 Patients must be assessed for morphologic compatibility before undergoing PPVI. An interventional cardiologist performs the procedure, which usually takes one to two hours. The procedure requires placing the patient under general anesthesia but does not require subjecting the patient to a cardiopulmonary bypass machine or making an open-chest incision. Patients are expected to stay in the hospital for one night and to be fully functional within a week after the procedure.22

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