Transcatheter pulmonary valve implantation: a melody to follow

This editorial refers to ‘Acute and midterm outcomes of the post-approval MELODY Registry: a multicentre registry of transcatheter pulmonary valve implantation’†, by J. Nordmeyer et al., on page 2255. Surgical repair of complex congenital heart disease involving pathology of the right ventricular outflow tract (RVOT) or the pulmonary valve often entails insertion of a valved right ventricle to pulmonary artery (RV–PA) bioprosthetic conduit. Similar conduits are used in the Ross operation for aortic valve disease. While providing an attractive surgical option with a large span of available sizes and favourable short-term haemodynamic outcomes, these bioprostheses are prone to severe calcification and deteriorating valve function, resulting in stenosis, regurgitation, or both, leading to pressure and/or volume loading of the right ventricle. With the specific aim to postpone the need for surgical replacement of degraded valved RV–PA conduits through re-establishing the valve function by transcatheter insertion of a stented valve in patients operated on for tetralogy of Fallot, the Melody® valve (Medtronic, Minneapolis, MN, USA) was launched by Dr Philip Bonhoeffer in 2000 and became commercially available in 2006. Since then, transcatheter pulmonary valve implantation (TPVI) has become the first-line treatment of dysfunctional RV–PA conduits, not only in patients with tetralogy of Fallot but also, for example, after repair of truncus arteriosus, Ross procedure for aortic valve disease, and Rastelli repair for transposition of the great arteries. The early clinical adoption of the Melody® valve has facilitated the subsequent major clinical and commercial success of transcatheter aortic valve implantation (TAVI), and follow-up data from early implantations keep providing important information regarding valve longevity and clinical outcomes that may also be relevant in the wider context of TAVI. The long-term outcomes reported by Nordmeyer et al. in the current issue of the European Heart Journal 1 are therefore of utmost importance to all clinicians involved in transcatheter heart valve implantation. The study is based on the largest post-approval cohort of patients after TPVI with the Melody™ valve to date, and reports the outcomes 42 centres across Europe, Canada, and Saudi Arabia. The authors show mid- and long-term results with an acceptable—though non-negligible—event (death, re-operation, or re-intervention >48 h) rate of 4.2% per person after the index procedure. The registry data indicate that the risk of conduit rupture and coronary compression has declined over the first decade of use, most probably due to improved pre-procedural imaging in recent years allowing detailed visualization of conduit calcification and accurate assessment of the proximity between the RV–PA conduit and coronary arteries. Apart from pre-procedural imaging, risk of coronary compression has been assessed by coronary angiography during inflation of a non-compliant balloon in the RVOT, but this technique may not be safe due to risk of rupture of severely calcified conduits and was only used in a minority of cases. In contrast, balloon interrogation of the RVOT with a compliant balloon to visualize the ‘landing zone’ can be performed with low risk. Pre-stenting has become a standard, and the incidence of stent fracture has nearly vanished. Furthermore, the authors suggest that access to covered stents has diminished the risk of bleeding in relation to conduit rupture. Haemodynamic outcomes measured at 3 and 12 months post-procedure have been favourable, although no direct comparison with surgical valves has been conducted. Nordmeyer et al. report an annual risk of infectious endocarditis (IE) of 2.4%, which is in line with previous studies2–4 (Table 1). Importantly, the large number of patients included in the current registry study allowed for Cox regression analyses to determine the importance of suspected risk modifiers. The authors show that signs of ‘definite’ endocarditis (according to Duke criteria) carry a higher risk than ‘possible’ endocarditis. However, as mentioned by the authors, visualization of the stent valve is frequently difficult with transthoracic and transoesophageal echocardiography because of artefacts from the stent frame. As a consequence, intra-cardiac echocardiography (ICE) and [18F]fluorodeoxyglucose positron emission tomography/computed tomography angiography have increasingly been adapted as diagnostic tools.5 , 6 Incidence of infective endocarditis following implantation of the Melody® valve Declining incidence with more aggressive prophylaxis. Incidence of infective endocarditis following implantation of the Melody® valve Declining incidence with more aggressive prophylaxis. Interestingly, the authors find the degree of remaining RV–PA obstruction to correlate with risk of IE, and advocate an aggressive approach to diminish the RV–PA gradient. Accordingly, the data show reduced risk when the largest (22 mm) Ensemble® delivery system is used. However, it is important to observe that in this regard perfect may be the enemy of good, as overexpansion of conduits (in particular homografts) entails a risk of rupture as well as coronary artery compression. The introduction of TPVI with the Melody® valve has been a major breakthrough in the management of conduit dysfunction and for transcatheter heart valve implantation in general. Previous studies have shown good clinical outcomes which is supported by the study by Nordmeyer and colleagues, but some concerns persist, in particular regarding risk of IE. Although IE in relation to TPVI is often medically treatable and rarely lethal, an incidence of >2% per person year is still disturbing. A recent study, however, provides encouraging data on the effect of strict adherence to IE prophylaxis guidelines combined with provision of extensive information to the patient’s family, general practitioner, and dentist. Cools et al. show that such precautions reduce the risk of IE to <1% per person-year, which is similar to or lower than what is reported for surgical valves.7 Novel diagnostic tools such as ICE may further benefit handling and treatment of patients with suspected IE. As IE in Melody® valves seems to exhibit characteristics rarely found in native valves, including rapidly progressing valvar stenosis, detailed imaging of the stent and valve leaflets with ICE may offer diagnostic accuracy superior to Duke criteria. Furthermore, overlay of echocardiographic and computed tomography images is increasingly offered by fluoroscopy system manufacturers, and these multimodality imaging techniques will most probably also become more prevalent in TPVI. The Melody® valve is still in its first iteration, and future iterations may improve utility, safety, and versatility, as seen with the TAVI systems. In particular, valves better suited for implantation in native RVOTs are eagerly awaited. Although the Melody® (also in the current study), and the Sapien XT® and Sapien 3® (Edwards Lifesciences, Irvine, CA, USA) have all successfully been implanted in the native RVOT, self-expanding systems are likely to provide further versatility, particularly in the case of a large RVOT. In this regard, feasibility studies on the Medtronic Harmony® valve and the Venus P-valve are promising.8 , 9 This may potentially facilitate not only a less invasive treatment as compared with surgery, but also an earlier re-valving in patients with, for example, free pulmonary regurgitation after repair of tetralogy of Fallot with a trans-annular patch. The long-term benefit of this may include reduced morbidity and mortality. Despite small market shares within transcatheter pulmonary valves, TPVI pioneered transcatheter valves and the evolution of new techniques and devices for use in young patients with congenital heart disease has historically contributed significantly to other areas of structural interventional cardiology. Further development of TPVI warrants support and interest from both clinicians and the industry in order to improve the treatment options for these young patients with congenital heart diseases. Conflict of interest: L.S. has received consultant fees and institutional research grants from Edwards Lifesciences and Medtronic. M.R.S. has no conflicts to declare. The opinions expressed in this article are not necessarily those of the Editors of the European Heart Journal or of the European Society of Cardiology.