Editorial: Percutaneous pulmonary valve implantation: Better technology is on the way!

Transcatheter pulmonary valve replacement (tPVR) has the distinction of being the first percutaneous valve replacement in humans, writing a new chapter in cardiac therapeutics with the development of transcatheter valve technologies. This innovation has evolved as an attractive alternative to surgery and has allowed treatment of a growing patient population with congenital heart disease, minimizing the number of lifetime sternotomies and extending the life of previously implanted conduits. Building on the steep learning curve over the past decade, the current high procedural success rates and favorable outcomes have been accomplished after overcoming various serious hurdles, such as routine right ventricular outflow tract (RVOT) pre-stenting and careful assessment of any coronary artery compression. In this issue of the Journal of Interventional Cardiology, Oechslin et al1 report the first published Swiss experience with tPVR in adult patients with congenital heart disease. This is a single center study addressing the feasibility, safety and efficacy of tPVR. The findings of this study, as has been shown in multiple prior experiences, reaffirm the safety and high success rate of tPVR.2-4 The authors report the mid-term results in a cohort of 25 adult patients with median age of 28 years (19-68), who underwent tPVR using Melody (84%) and Edwards (16%) valves. The majority of patients had mixed pulmonary stenosis (PS) and pulmonary regurgitation (PR) in previously implanted conduits between the right ventricle and pulmonary artery. Clinical and echocardiographic data were obtained at baseline and yearly afterwards. They documented a median follow-up of 48 months, with the longest experience out to 58 months following tPVR. The Zurich group should be congratulated for demonstrating excellent results in a highly-complex group of patients, providing effective reduction of RVOT obstruction and excellent relief of regurgitation, with no or mild PR in all patients. In general the authors mentioned that pre-stenting was performed in the majority of cases. The purpose of pre-stenting when the Melody valve is used is to reduce the incidence of stent/valve fracture and in the case of Edwards valve is to provide a landing zone for the short valve. Two major intra procedural complications were encountered; pulmonary artery wire perforation and tricuspid valve damage following entrapment of the delivery system. However, no mortalities were reported and only 2 patients (8%) required reintervention, of which one of them did not previously undergo RVOT pre-stenting. Despite the small cohort of patients and relatively short follow-up period, these results compare very favorably with other experiences around the world. Multiple studies have previously demonstrated very good short- and medium-term results; however, long-term follow-up data remains largely lacking. The longest and largest published experience to date, the US Melody valve Investigational Device Exemption trial, reported 150 valve implants, with all patients at least four years from implant, and longest follow-up to seven years.5 There was a disappointing freedom from reintervention of 76% at five years and stent fracture documented in 50 patients, with the majority being managed with further catheter intervention. It is important to note that only 10% of the patients underwent RVOT pre-stenting in the first tertile of this trial and the main cause of valve dysfunction appeared to be related to stent fracture. This led to significant changes in procedural practices over the years, of which RVOT pre-stenting to preserve the integrity of the Melody valve stent has been the one with the highest clinical impact and evolved to become common practice in most centers. This Swiss report, having learnt from other experiences, emphasizes the importance of pre-stenting and optimal preparation of RVOT conduits. This step before valve implantation reduces the radial load on the bioprosthesis and the incidence of stent fracture, which remains the leading cause of RVOT reintervention. In this series, the majority of patients underwent RVOT pre-stenting, of which 40% of patients received more than one stent, effectively eliminating the need for reintervention. Although it is known that pre-stenting protects against stent fracture and RVOT reintervention, it is not known whether different numbers or types of stents are related to these outcomes. Pooled data from Melody valve multicenter studies showed lower incidence of stent fracture among multiple pre-stenting patients; however, freedom from any kind of reintervention between single versus multiple pre-stent patients was not different and longer-term data is still needed.6 Furthermore, optimal preparation of RVOT conduits often using high-pressure balloons comes with a risk of tear and rupture. The risk of conduit rupture has been reported in almost 6% of patients with many operators now choosing elective placement of a covered stent in patients with heavily calcified conduits.3, 7 The pre-market approval of the covered CP stents (NuMED Inc., Hopkinton, New York) in the United States added an invaluable tool to our armamentarium for the prevention and treatment of most conduit injuries. There is general consensus that symptomatic patients with RVOT dysfunction should undergo pulmonary valve replacement,8 however, the timing of intervention in asymptomatic patients remains a matter of debate. The existing evidence supports intervention in asymptomatic patients with RVOT stenosis (peak Doppler systolic gradient>50 mmHg) or mixed PS/PR with an expected improvement in exercise capacity,9 however, there is little data to suggest improvement in clinical outcomes in patients with predominant PR. Several studies have shown improvement in right ventricular (RV) volume and systolic function with intervention in patients with predominant PR at certain volumetric/systolic function thresholds (right ventricular end-diastolic volume index of 150 to 170 mL/m2, right ventricular end-systolic volume index of 80 to 90 mL/m2 or right ventricular end-diastolic volume twice left ventricular end-diastolic volume), however, these did not translate into improvement in hard clinical endpoints.10-12 Similarly, Lurz et al demonstrated no improvements in exercise capacity in patients with predominant PR, on the other hand such benefits were seen in patients with predominant PS.13 Despite the improvement in functional class, the current Swiss report fails to demonstrate significant improvement in RV dimension or cardiopulmonary exercise testing following tPVR. Nevertheless, as the authors highlight in their discussion, the small cohort of patients and lack of MRI follow-up data limit the interpretation of these results. Further long-term cohort-outcome studies are still needed to optimize the timing of pulmonary valve replacement especially in the PR predominant population. Lastly, the group of patients that can be helped by the currently approved technologies (Melody/Edwards) are limited to those with a conduit/bioprosthetic valves between the right ventricle and pulmonary artery. This group comprises only about 25% of patients requiring valve implantation. This leaves about 75% of patients who underwent “transannular patch enlargement of the right ventricle outflow tract with resultant severe pulmonary regurgitation”. So, the question to answer, is there anything we can do for such patients? The good news is that there are at least 2 valves being evaluated in clinical trials outside the United States (Venus P valve-Venus Medtech, China) and in the United States (Harmony valve-Medtronic) for patients without conduits. The initial results from the use of these valves are encouraging.14, 15 In addition to these two new valves, a new stent (Right ventricle outflow tract reducer) called Altera from Edwards is being evaluated in the United States with potential implantation of the Edwards Sapien 3 valve inside, thus allowing the use of currently available and approved valve to help patients with large right ventricle outflow tract. It is clear that tPVR techniques/technologies will continue to evolve and the problem of stent fracture, large RVOTs and reinterventions in the early experience of tPVR has improved with routine RVOT pre-stenting and the novel development of new valves and stents. However, long-term data are still required to make final judgments on the long-term outcome of these patients with novel valves/stents. This is a very exciting era for percutaneous cardiac therapies with several emerging technologies have recently opened new perspectives to further expand the applicability of transcatheter pulmonary valve replacement to a broader population of patients. Dr. Hijazi is a consultant for Venus Medtech.