In pediatric patients, valvular diseases are mainly secondary to congenital defects or rheumatic fever, constituting a significant source of global morbidity and mortality. Congenital mitral valve disease is rare compared to acquired conditions secondary to rheumatic fever, ischemic heart disease, or degenerative mitral disease in the elderly.
Congenital mitral valve disease may occur in isolation, be associated with other anomalies such as atrioventricular septal defects or dilated cardiomyopathy, or form part of Shone’s syndrome. In neonates and infants, stenosis predominates, often presenting with hammock-like valves with rigid leaflets and anomalies of the subvalvular apparatus, such as a parachute valve with a single papillary muscle. In older children, mitral regurgitation due to leaflet prolapse or chordal rupture is more common.
When mitral valve disease requires surgery, an initial repair is preferred, which in children shows good results, minimal hospital mortality, and favorable long-term outcomes, with acceptable reintervention rates during follow-up. Neonates and infants, however, present worse outcomes in terms of mortality and morbidity compared to older children, as they represent the most severe end of the mitral valve disease spectrum. Nonetheless, if a mitral repair in infants is successful and no reintervention is needed within the first two postoperative years, long-term prognosis is excellent and comparable to repairs performed in older children.
Mitral valve repair in pediatrics allows for time to be gained, acknowledging the likelihood of future reintervention during the patient’s lifetime. When repair is no longer feasible, valve replacement becomes necessary, ideally when the patient reaches adulthood, as this allows for more technical options and improved outcomes. With current advancements, many children with congenital valvular disease will reach adulthood, making it likely that the need for valve replacement will increase as these patients transition from adolescence.
The mitral valve, located posteriorly within the heart, consists of the annulus, leaflets, and a subvalvular apparatus comprising chordae and papillary muscles. This anatomy makes its surgical access more challenging compared to other cardiac valves. In children, alternative approaches such as transseptal or superior septal access are often required to achieve adequate visualization of the valve. Pediatric cases pose additional challenges, considering factors such as the size of the patient, the left atrium, and the mitral annulus, future growth, physical activity levels, and in females, menstruation and potential future pregnancies.
When mitral valve repair is not feasible or fails, the valve must be explanted and replaced with a prosthetic substitute, which is more complex in pediatric patients compared to adults. Implanting a mitral prosthesis should avoid an intra-annular position to prevent circumflex artery damage, posterior atrioventricular groove rupture, subaortic stenosis due to prosthesis protrusion into the left ventricular outflow tract, or conduction system damage causing complete atrioventricular block. Retaining parts of the subvalvular apparatus with papillary muscles is essential to ensure it does not interfere with prosthesis function. If the entire subvalvular apparatus is removed to fit the prosthesis, the left ventricular geometry is altered, increasing the likelihood of dysfunction. The only effective method for annular enlargement is the mitro-aortic David procedure, which involves sacrificing the aortic valve as collateral damage.
The greatest surgical challenge lies in the smallest patients, weighing less than 10 kg, who often present with complex mitral valve disease and significant preoperative comorbidities, including pulmonary hypertension and failure to thrive, leading to worse postoperative outcomes and higher mortality compared to older children. These patients frequently have small mitral annuli and left atria, significantly limiting technical options. In this age group, surgery is always palliative, as any valve substitute will have a limited lifespan and require replacement in the future due to the child’s growth, while the implanted prosthesis remains fixed in size. Hospital mortality rates for mitral valve replacement in infants range from 5–30%, with poorer outcomes in those younger than two years with small prosthetic sizes.
Mechanical prostheses are currently the best option for mitral annuli larger than 15 mm due to their durability and resistance to degeneration. However, over time, pannus growth may cause stenosis or interfere with proper function. These prostheses require lifelong anticoagulation, which is more challenging in small patients, with increased difficulty achieving a therapeutic range and greater risk of thromboembolic complications. The smallest available prosthesis on the market is currently 15 mm. These prostheses can be placed in an intra-annular, partial, or fully supra-annular position or mounted on a Gore-Tex or Dacron conduit using the “chimney” technique, ensuring the pulmonary vein return to the left atrium is not obstructed.
Bioprostheses with stents have a higher profile than mechanical prostheses, with the smallest size being 19 mm. Their implantation requires confirmation that prosthetic commissures do not obstruct the outflow tract or damage the free wall of the left ventricle. While they do not require prolonged anticoagulation, their disadvantage in pediatric patients is accelerated calcification, contributing to early deterioration.
Melody® bioprostheses, constructed from bovine jugular veins and supported by a stent, were initially designed for percutaneous pulmonary valve replacement. These prostheses have been hybrid-implanted in the operating room by pediatric cardiac surgeons and interventional cardiologists on a compassionate basis as mitral substitutes when the annulus is smaller than 15 mm, yielding good initial and mid-term results. This approach is safe, effective, reproducible, and allows for redilation during follow-up to accommodate the child’s growth, without requiring lifelong anticoagulation. The stent is bent to shorten the prosthesis’s profile to 20 mm, ensuring it does not obstruct pulmonary vein drainage or cause left ventricular outflow tract stenosis.
Alternative surgical techniques to avoid long-term anticoagulation remain limited in use and experience among small children. The inverted pulmonary autograft placed in the mitral position (Ross II procedure) is technically complex and may necessitate future reinterventions at both the pulmonary and mitral sites. Homograft interposition in children is associated with higher degeneration rates due to accelerated calcification and immune responses, potentially leading to hypersensitization that contraindicates future transplantation.
Tissue engineering studies aim to create living valves tailored to each patient’s anatomy and needs, with the capacity for growth, repair, and remodeling. Initial results in animal models show promise but reveal early degeneration within six months, highlighting the need for further research before advancing to human clinical trials.
A recent publication discussed on this blog involving partial semilunar valve transplants in pediatric patients offers promising possibilities. While the long-term durability of these transplants remains to be evaluated, initial results show adequate valve function with low doses of immunosuppressants during follow-up.
There is still no ideal valve substitute: one that offers good hemodynamics, availability, biocompatibility, and properties akin to the native mitral valve’s flexibility, durability, and strength, free from degeneration, calcification, or infection, requiring no anticoagulation, capable of growth and remodeling, and cost-effective for widespread use. Current evidence strongly supports mechanical prostheses for annuli larger than 15 mm and Melody® prostheses for annuli smaller than 15 mm as the best available options.
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