Surgical correction of congenital heart diseases (CHDs) that involve the right ventricle outflow tract (RVOT) favors anatomical and functional alterations of the pulmonary artery valve and trunk in the late post-operative period. For the correction of these alterations, the patient must undergo new surgical events that require implantation of biological devices such as allografts and bioprostheses, among others, which usually deteriorate as a consequence of an adaptive patient response that modifies their geometry, favors caliber reduction and blood flow reduction, which clinically is observed as functional class deterioration, with significantly high morbidity and mortality rate being associated with these reoperations¹-⁴.

In the late 20^th century, it was thought that pulmonary valve insufficiency, one of the usually described CHD surgical repair complications that involve RVOT, would be well tolerated by the right ventricle (RV); however, experiences observed in recent years have shown that an important number of patients evolve to right heart failure, lethal arrhythmias, and sudden death⁵-⁹. Current criteria after RVOT repair in patients with complex CHD, such as tetralogy of Fallot, include clinical criteria (functional class, signs of heart failure) and RV functional variables (ejection fraction, end-systolic [ESV], and end-diastolic volume [ESV])⁹.

Since most patients with CHD that involves RVOT will require reoperation during their lifetime, the need for options to improve approaching strategies and decrease primary correction reoperation complications was a reason for the development of new technologies aiming to restore the blood flow to the pulmonary circulation, with percutaneous technology appearing for the implantation of pulmonary bioprostheses¹-⁹.

In 2000, Dr. Bonhoeffer performed percutaneous implantation of a pulmonary valve in a 12-year-old patient with significant RVOT obstruction for the 1^st time; this fact was the basis for the development of the Melody^® percutaneous valve¹⁰. Two years after the first percutaneous implantation, the first series of eight patients with percutaneous valve successful implantation in pulmonary position was published¹¹, and in the next few years, the learning curve and technology evolution allowed to demonstrate the safety and efficacy of this approach, mainly a less invasive method, with less bleeding risk and less infectious complications in comparison with the surgical approach¹¹,¹².

The Medtronic Melody^® valve (Medtronic Inc., Minneapolis, MN, USA) was approved by the Food and Drug Administration in 2010 as part of the alternatives for the treatment of LVOT dysfunction¹³. Since then, its use has spread quickly, and today, more than 10,000 percutaneous valve implantations with this method are reported in the world¹⁴. The Melody^® valve consists of a 34-mm platinum-iridium bare stent (CP stent, NuMED Inc.; Hopkinton, New York, USA), with one valve made with a bovine jugular vein segment. The device is attached to a balloon catheter and released on a 22-Fr sleeve¹-¹⁰. Despite its size, the use of the Melody^® valve was intended for those patients with RVOT diameters of < 24 mm, which limited the benefit to a specific group of patients. Thus, the need for options for RVOT of larger diameter led to the development of Edwards’ Sapien^® valve (Edwards Lifesciences INC., Irvine, CA, USA), thus expanding the possibility of a percutaneous approach to RVOTs with a diameter larger than 29 mm, mainly in prosthetic conduits; and in specific situations, in selected patients with native tracts¹⁵.

Although the Melody^® valve is the most widely used device for the percutaneous implant, worldwide studies show similar results in terms of its medium-term results, despite the fact that the first post-implant follow-up series indicate higher residual gradients with the use of the Sapien^® device¹⁶. Current criteria for prosthetic valves percutaneous implantation in the RVOT are divided according to the presence or absence of symptoms and include:

One of the principles for the decision of this alternative for RVOT dysfunction is to precisely understand the anatomy. Analysis of each case is necessary and involves imaging studies, heart rate evaluation, hemodynamic evaluation, stress tests, and complementation of the function with the use of cardiac magnetic resonance imaging (CMRI) and cardiac computed tomography (CCT)¹¹-¹³,¹⁸. Furthermore, there are different factors to determine the possibility of percutaneous implantation, with the most interesting being: (a) RVOT morphology, (b) RVOT distensibility and compliance, and (c) coronary anatomy. Up to five RVOT morphology types have been described; the prototype (due to its frequency) is the pyramidal morphology, where the base is wider with progressive narrowing toward its most distal part, which is also the most complex for placement. When this technique started being used, patients with native tracts were practically discarded as percutaneous treatment candidates; however, with the advent of techniques such as pre-stent, the Panorama was improved for these cases in which implementation of this technique became possible¹⁸-²⁰.

RVOT distensibility and compliance can be characterized with techniques such as CCT and CMRI, which allow assessing the degree of obstruction, calcification, and pulsatility. Coronary anatomy is another essential factor, given the relationship with RVOT and increased risk of coronary occlusion during implantation⁵,¹⁷-²⁰. Current standard indications for prosthetic valve percutaneous implantation include RVOT dysfunction in patients with prosthetic conduits, as well as dysfunction of surgically placed valves using the procedure known as valve-in-valve; and current case series even suggest the safety and efficacy of the use of these devices in native tracts with the alternative of techniques such as pre-stent, which in addition reduces the risk of complications such as fractures and the need for reioperation¹⁹,²⁰.

The use of the percutaneous procedure involves risks and complications, starting with the technique during its placement: coronary occlusion, ischemia, and perforation. Post-placement complications include, among the most common: stent fracture, paravalvular leaks, endocarditis, thrombosis, and valve stenosis. Infective endocarditis has been identified as a significant complication after implantation, with the reported incidence being 2.5-4%/patient-year¹⁷. No specific characteristics have been determined regarding its microbiology, although there are series that report lower frequency¹⁷,²¹.

Initial experience has identified stent fracture as the complication with the highest potential, which increases the risk of stenosis, insufficiency, or embolization; in this context, stent fracture is the most common cause of reoperation, with its cause being attributed to a significant increase in stress by volume overload, most times without stent integrity loss (type 1) and without implying clinical significance. The factors with the highest association are young patients (including pediatric patients), high RVOT gradients, and small RVOT diameters, with the incidence of this complication being lower than 20% of cases²².

These percutaneous-implantation devices have shown in the USA and in European countries very low morbidity and practically no mortality and have become a real tool for patients with these complications, who also have elevated surgical risk¹,¹⁰-²¹.

Considering the elevated cost of this technology, its arrival to Mexico has been limited; however, development in training at the pediatric interventionism department of the 20 de Noviembre National Medical Center (CMN – Centro Médico Nacional) has promoted its acquisition, with good results in its implantation for correction of anatomical anomalies of patients undergoing a primary surgical correction, who present with long-term deterioration. We present the experience with Melody^® valve percutaneous implantation in four cases attended to at the Pediatric Cardiology Department of ISSSTE CMN 20 de Noviembre.

From January 2016 to December 2017, four patients (three females) with an average age of 19.2 years and weight of 52.7 kg underwent Melody^® valve percutaneous implantation. The predominant diagnosis was tetralogy of Fallot (75%). Two of the patients showed pulmonary insufficiency progressive increase on echocardiographic follow-up and two showed significant RVOT stenosis. Two patients had prosthetic conduits in ventriculopulmonary continuity and two required previous pulmonary valve surgical replacement. All four patients underwent pre-stenting, in different variants (see description in each case), as well as coronary circulation evaluation. The characteristics are described in Table 1 and Fig. 1.

Figure 1 A: Case 1. Edwards^® prosthetic valve rupture sequence with an Atlas^® balloon. B: Case 2. pulmonary branches sequential plasty. C: Case 3. Melody^® valve pre-stenting and opening on the balloon. D: case 4. Melody^® valve placement on prosthetic ring.