NEW YORK – Physicians at Boston Children’s Hospital have replaced the mitral valves of eight infants with irreparable mitral valve disease with a valve that offers the opportunity of sequential expansion as the child grows, according to Dr. Sitaram M. Emani, who described the results at the 2013 Mitral Valve Conclave.
"The Melody valve retains its competence if you expand it before putting it in. We asked whether the valve retains the ability to maintain competence even if expansion is performed after implantation as the patient grows," said Dr. Emani, a pediatric cardiac surgeon at Boston Children’s Hospital.
Dr. Sitaram Emani
According to Dr. Emani, the current options for infants with damaged mitral valves that are beyond repair are replacement with mechanical or bioprosthetic valves or the Ross mitral procedure. Perhaps the main disadvantage of these options is the lack of a prosthetic valve small enough for an infant, one that is less than 12 mm in diameter. Another problem is the possibility of stenosis developing as the child grows, since the diameters of the prosthetics are fixed. Other drawbacks are that supra-annular fixation is generally associated with poor outcomes and that annular fixation limits the ability to upsize at reoperation.
The Melody valve is an externally stented bovine jugular vein graft that was designed for transcatheter pulmonary valve replacement. In this study, the valve was inserted surgically. The valve maintains competence over a range of sizes up to 22 mm. Although this valve is not approved for use for mitral valve replacement, the hope of using such a prosthetic is that it can be enlarged in the catheterization laboratory as the child grows.
Dr. Emani conducted a retrospective study of his experience with the Melody valve for mitral valve replacement in eight infants less than 12 months of age. The median age at implantation was 6 months (range, 1-9 months). Four infants had an atrioventricular canal (AVC) defect and four had congenital mitral valve stenosis. Most of the children had two prior operations for mitral valve repair. The longest follow-up to date has been 2 years.
At a median follow-up of 8 months, regurgitation on the echocardiogram was considered to be mild or less in all patients. The median gradient was 3 mm Hg (range, 2-7 mm Hg) on the immediate postoperative echocardiogram. Three patients developed a mild paravalvular leak; one of these patients had undergone aggressive stent resection, a modification Dr. Emani does not recommend. One patient developed left ventricular outflow tract obstruction (LVOTO), which Dr. Emani attributed to the lack of distal stent fixation in this patient. Another patient with an AVC defect developed complete heart block.
One patient who died 3 days postoperatively had heterotaxy, severe mitral regurgitation, and prior ventricular failure on extracorporeal membrane oxygenation support. That patient had undergone valve implantation as a last resort.
Three patients underwent sequential expansion about 6 months after implantation. After valve expansion, the median balloon size was 12 mm, ranging from 12 to 16 mm. None of the patients developed worsening valvular function and all had relief of obstruction. Transcatheter intervention was used to correct a paravalvular leak in one patient and to treat a left ventricular outflow tract problem in another. None of the patients developed endocarditis or a strut fracture, "although I worry about strut fracture if aggressive stent resection and manipulation is performed," Dr. Emani said at the meeting, which was sponsored by the American Association for Thoracic Surgery.
Dr. Emani offered some procedural tips. First, the Melody valve must be optimized for surgical implantation in infants. The length of the valve must be reduced by trimming it to reduce the chance of LVOTO or pulmonary vein obstruction. He recommends sizing the valves by echocardiogram and fixating the distal stent to the inferior free wall of the ventricle.
Although he has used both circumferential and four-point fixation, Dr. Emani has learned all that is really needed to prevent leakage is friction of the stent against the annulus. Early on he used a pericardial cuff to anchor to the annulus, particularly in patients who had undergone failed AVC repair. He tries to preserve at least part of the anterior leaflet to facilitate suture placement and create a "stand-off" from the LVOTO.
Dr. Emani also advised limiting intraoperative dilation to no more than 1 mm greater than the measured annulus. "Try not to overdilate at implantation to avoid heart block, LVOTO, and coronary compression. The nice thing is you don’t have to decide then and there what size you want. You can go back to the cath lab and, under direct visualization with the coronary view, you can dilate it under more controlled circumstances.