Summary
Since the first transcatheter implantation of a pulmonary valve in 2000 in a twelve year-old boy with a dysfunctional right ventricle to pulmonary artery conduit by Philip Bonhoeffer and Younes Boudjemline, the Melody ® valve has become worldwide used. It represents an efficient alternative to open-heart surgery. We aimed in this comprehensive review to describe the current indications of percutaneous pulmonary valve implantation, the devices currently used and the clinical results.
Résumé
Depuis la première implantation percutanée d’une valve pulmonaire en 2000 chez un garçon de 12 ans avec un conduit défaillant entre le ventricule droit et l’artère pulmonaire, par Philip Bonhoeffer et Younes Boudjemline, la valve Melody ® est devenue d’utilisation courante dans de nombreux pays. C’est une alternative efficace à la chirurgie conventionnelle à cœur ouvert. L’objectif de cette revue non systématisée est de décrire les indications actuelles du remplacement pulmonaire percutané, les prothèses actuellement utilisées et les résultats cliniques.
Historical background
Percutaneous pulmonary valve implantation (PPVI) is a major advance in the interventional treatment of congenital heart diseases. Transcatheter relief of pulmonary valvar stenosis was first performed in 1953 by balloon angioplasty . Since the development of open-heart surgery in the late 1950s , treatment of pulmonary valve or right ventricular to pulmonary artery conduit (RVPA) regurgitation was entirely surgical. Need for repeated surgeries in high-risk patients yield the need for a transcatheter solution. The first percutaneous transcatheter implanted valve was described by Davies et al., in 1965 to treat experimentally induced aortic regurgitation in dogs . However, it is not until 1992 that Andersen et al., further reported the successful delivery of a catheter-mounted, balloon-expandable stent valve in the aortic position in pigs . The same year, a prosthetic caged-ball aortic valve was also successfully deployed percutaneously in dogs by Pavcnik et al. . The first transcatheter pulmonary valve was developed by Philipp Bonhoeffer and Younes Boudjemline in the late 1990s. A valved segment of a bovine jugular vein was sewed into a balloon-expandable vascular stent. Transcatheter pulmonary valve replacement was successful in animals . Soon after, the first human transcatheter cardiac valve replacement was successfully reported in a twelve year-old boy with a dysfunctional RVPA conduit . Medtronic inc. further conducted the in-vitro testing to complete the design process of the named Melody ® transcatheter pulmonary valve. European certification was obtained in 2006 as well as Health Canada approval, making it the first commercially available transcatheter valve in the world. A Melody ® valve was implanted in the 100th patient in 2005 and in the 1000th patient in 2009. The Melody ® valve was approved for use in the United States of America in 2010. Since 2000, many clinical studies have reported early and mid-term outcome and more than 6000 valves have been implanted worldwide . The Edwards ® valve (Edwards SAPIEN ® pulmonic transcatheter heart valve, Edwards Lifescience, Irvine, CA, USA) was initially used for transcatheter aortic valve replacement but then also for PPVI. It has reached CE certification for PPVI in 2010. First implantation was performed in 2006 in USA and in 2010 in Europe . Clinical results in the first implanted patients have subsequently been published .
Concept sustaining percutaneous pulmonary valve implantation for the management of congenital heart diseases
Incidence of congenital heart disease is approximately 8 out of 1000 babies. Around 20% of congenital heart diseases involve the right ventricle outflow tract (RVOT) and the pulmonary valve. Surgical palliation of many complex congenital heart diseases, including tetralogy of Fallot (TOF) with pulmonary atresia, truncus arteriosus, some forms of transposition of the great arteries, double-outlet right ventricle, Ross surgery for aortic valve disease and others, involves interposition of a conduit between the right ventricle and the pulmonary artery in the first months of life. Valved conduits are composed of synthetic material or non-viable homograft or xenograft tissue. Inability to follow the child growth, mechanical distortion and progressive degeneration lead to conduit stenosis over time. Regurgitation appears with degeneration of the leaflets. Other congenital heart diseases require enlargement of the RVOT by a trans-annular patch during the surgical correction, frequently leading to pulmonary valve regurgitation (TOF with pulmonary stenosis, pulmonary valve agenesis and others). Pulmonary valve regurgitation may complicate transcatheter dilation of pulmonary valvar stenosis and surgical valvulotomy. Isolated congenital pulmonary regurgitation remains an uncommon cause of pulmonary valve replacement .
An obstructed RVOT induces a pressure overload in the right ventricle (RV). A pulmonary regurgitation leads to a volume overload and thus to a dilation of the RV . Both obstruction and regurgitation may be combined. These lesions are often long well tolerated but the overload of the RV is progressively deleterious for the right ventricular function and then ultimately for the patient . Impaired exercise capacity, atrial and ventricular arrhythmias, sudden deaths after complete repair of TOF are related to the severity of the pulmonary regurgitation and lead to an increased overall mortality after the second decade .
Restoration of pulmonary valve competence and relief of RVOT obstruction are beneficial. It reduces ventricular overload, increases right and left ventricular performance , functional ability and cardio-respiratory exercise performance . It may also help to control preexisting atrial and ventricular arrhythmias in TOF patients .
RVPA conduit obstruction was the most frequent reason for surgical re-intervention . Transcatheter relief of post-operative RVOT obstruction was early attempted with balloon angioplasty. However, ineffective relief was observed in many cases due to elastic recoil and non-expandable conduit. Intravascular stenting further helped to increase efficiency of these percutaneous procedures but at a price of a free pulmonary regurgitation that may be symptomatic in some cases . PPVI seemed therefore promising to treat RVOT obstruction without inducing pulmonary regurgitation but no studies are available to compare the outcome of both strategies (non valved stent vs. valved stent). Until PPVI, treatment of RVOT regurgitation required open-heart surgery. Despite improved surgical technique and good mid-term outcome, the surgery carries short-time morbidity in these patients with multiple previous procedures. It starts again the conduit duration countdown. Around 50% of conduits still require replacement within 10 years . Second and subsequent conduits have shorter survival than the original implants . Less procedural morbidity existing with PPVI offered a new solution for the management of these patients. PPVI allows concomitantly relief of RVOT obstruction and regurgitation, maintaining pulmonary valve competence . PPVI restores right ventricular load within normal range. An early improvement of biventricular performance is observed following relief of RVOT obstruction, with decrease right ventricular volumes, increased right and left ventricular systolic function and increased cardiac output . Relief of obstruction also improves early left ventricular filling properties. This improvement is not only related to the increase in right ventricular forward flow but also to a more favorable ventricular interaction . After PPVI, dyspnea degree decreases and exercise tolerance is rapidly improved . This is less clear in case of PPVI indicated for pulmonary regurgitation without RVOT obstruction and is related like with surgical replacement to the degree of RV dilation at the time of replacement . The acute effects of PPVI are maintained over time without evidence for further ventricular remodeling or positive functional evolution beyond the early post-operative period .
Indication for percutaneous pulmonary valve implantation, current official guidelines
Recommendations for PPVI match those for surgical pulmonary valve replacement, with specificity regarding feasibility and outcome of the percutaneous implanted valves.
In Europe, the European society guidelines stipulate that pulmonary valve replacement should be performed in symptomatic patient with severe pulmonary regurgitation and/or RVOT obstruction (Tricuspid velocity > 3.5 m/s, right ventricular systolic pressure > 60 mmHg). In asymptomatic patients with severe pulmonary regurgitation and/or RVOT obstruction, PPVI may be considered if there is an objective decrease in exercise capacity, a progressive right ventricular dilation, a progressive right ventricular systolic dysfunction, a progressive tricuspid regurgitation, sustained atrial or ventricular arrhythmias, right ventricular systolic pressure > 80 mmHg or peak tricuspid regurgitation velocity > 4.3 m/s .
In France, the “Haute Autorité de santé” stipulates that PPVI is indicated to treat RVPA conduit or xenograft dysfunction, with a minimal internal diameter of 16 mm. PPVI in a native RVOT or in child weighting less than 20 kg is not indicated .
The Food and drug administration instructions for use under a humanitarian device exemption stipulate that the Melody ® PPVI is indicated in the management of pediatric and adult patients with the existence of a full circumferential dysfunctional RVOT conduit that was equal to or greater than 16 mm in diameter when originally implanted. The dysfunctional RVOT conduit is retained as an indication for PPVI if the regurgitation is equal to or greater than moderate and/or if the mean RVOT gradient is equal to or greater than to 35 mmHg. The scientific statement from American Heart Association endorsed this recommendation .
Current devices
Melody ® transcatheter pulmonary valve and Ensemble ® delivery system
The Melody ® valve (Medtronic Inc., Minneapolis, MN, USA) is the first valve inserted percutaneously in humans. It is the most used valve in the world in pulmonary position. Most of the available data for PPVI are coming from its use. The device is made of a bovine jugular vein valve (Contegra Pulmonary Valved conduit, Medtronic Inc., Minneapolis, MN, USA) sutured within a Cheatham-Platinium stent (CP stent, NuMED Inc., Hopkinton, NY) ( Fig. 1 ). The bovine jugular vein is different from the surgical implant. It is trimmed to reduce its thickness before suturing in the vascular stent. Its length is shorter than the Contegra and equal to the length of the CP stent (CP8Z34).
At the moment, there is only one size. It is a one-sized valve of 18 mm in diameter that is crimped to 6mm and balloon expanded from 18 to 22 mm in diameter. The bovine jugular vein has thin, compliant leaflets with deep commissures that provide exceptional coaptation of the leaflets at various internal diameters. It opens fully and close readily with a minimum of pressure. The vein tissue has a thickness of less than 0.5 mm. The vein segment is manually sutured to the stent frame at every stent node. Complete suture lines are also done at the inflow and outflow part of the stent. The CP stent has a closed-cell design with six rows of circumferential struts. Each row is made of a platinium-iridium wire that is welded in a zig pattern to form eight crowns. The zig-to-zig welds are gold-brazed to increase their strength. The stent measures 3 mm in length in an unexpanded configuration and 26.2, 24.2 and 23 mm when implanted at 18, 20 and 22 mm respectively. This stent was chosen by Bonhoeffer and Boudjemline because it is a good compromise between rigidity for the radial force and malleability for the manual crimping. It has a good radio-opacity, a good conformation, is easy to crimp on a balloon and has a foreshortening to a degree that does not distort the valve leaflets. The Melody ® valve manufacturing follows a step-by-step rigorous process and testing before commercialization . As a result, less than 5% of bovine jugular veins are available for PPVI. Because of availability problem with the bovine jugular vein, Medtronic is introducing a new Melody ® manufactured with a 16-mm valve that would works for patients up to 20-mm. Its introduction is programmed for Europe at the end of 2014.
The Melody ® valve is implanted through a dedicated delivery system (Ensemble ® Transcatheter Delivery System, Medtronic Inc., Minneapolis, MN, USA). It consists of a balloon-in-balloon (BiB, NuMED Inc., Hopkinton, NY) catheter delivery system with a retractable sheath that covers the Melody ® valve once it is crimped over the balloon ( Fig. 2 ). The BIB balloon allows repositioning during the valve delivery ( Fig. 3 ). The outer balloon is available in 3 sizes: 18 mm, 20 mm and 22 mm in diameter. The thickness of the valve stent assembly is approximately 1 mm resulting in an outer diameter of 2mm more than the diameter of the delivery balloon. A sheath with side port allows flushing the system and acts as a homeostatic sleeve to minimize bleeding at the insertion site. The outer diameter at the top of the delivery system is 22 Fr .
