FROM JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY
Mitral valve replacement in infants and young children is complicated because appropriately sized prostheses are difficult to come by and these patients need replacements later on as they continue to grow – thus the high rates of reintervention and death. Pediatric cardiac surgery specialists at Boston Children’s Hospital are among the few that have used stented jugular vein grafts in these patients, and they have reported on a refinement of their technique that uses echocardiography before and after graft placement to obtain valuable measurements for sizing and implanting a prosthesis and for identifying patients at risk of complications.
Lindsay R. Freud, MD, and her associates reported in the January 2017 issue of the Journal of Thoracic and Cardiovascular Surgery on pre- and postoperative echocardiograms of 24 patients who had mitral valve replacement (MVR) with the Melody stent-mounted, valved bovine jugular vein graft (Medtronic) ( J Thorac Cardiovasc Surg. 2017;153:153-60 ). The device, which is approved for transcatheter pulmonary valve replacement, was adapted for implantation into the mitral position, an indication that is not yet Food and Drug Administration approved. “With the increasing use of the Melody valve in the mitral position in infants and young children, we sought to provide a framework for both pre- and early postoperative echocardiographic assessment,” Dr. Freud and her coauthors said.
Infants and small children have been a challenging population for MVR because the lack of appropriately sized prostheses complicates outcomes. The Melody valve is approved for transcatheter pulmonary valve replacement. In 2012, surgeons at Children’s Hospital Boston first reported on adapting the Melody valve in infants with mitral valve disease ( Ann Thorac Surg. 2012;94;e97-8 ) because it could be tailored to the small annulus and could be expanded via catheterization as the recipient grows, avoiding the need for some reoperations.
“The potential dimensions often had normal z scores with fair correlation with intraoperative Melody dilation,” the investigators said. They also found that a ratio of the narrowest subaortic region in systole to the actual MV dimension (SubA:MV) less than 0.5 was associated with postoperative left ventricular outflow tract obstruction (LVOTO), which occurred in four patients. The median age of the study group was 8.5 months.
“Postoperatively, mitral gradients substantially improved, with low values relative to the effective orifice area of the Melody valve,” Dr. Freud and her associates said. None of the patients had significant regurgitation or perivalvar leak.
In early reports of the Melody valve in infants and small children, the surgeons determined the size of the replacement valve during the operation itself. Despite encouraging early results, reports of complications such as LVOTO soon followed. The Children’s Hospital Boston researchers undertook the study to determine if echocardiography before surgery would help to identify the correct valve size for expansion and predict which patients would be at risk for LVOTO.
“The preoperative SubA:MV ratio may help assess the risk for postoperative LVOTO, which is an important complication,” Dr. Freud and coauthors said. The presence of LVOTO preoperatively was also a risk factor, but only one of eight patients with an atrioventricular canal defect developed LVOTO. In patients with a SubA:MV ratio less than 0.5, preoperative LVOTO, or any other anatomic risk factor, surgeons should consider options to prevent LVOTO, Dr. Freud and her associates said. Those alternatives include more aggressive resection of stent material, atrial displacement of the valve, or less aggressive distal expansion of the valve.
Postoperative echocardiography enabled Dr. Freud and her coauthors to outline baseline values for the Melody valve in the mitral position by maximum intraoperative balloon diameter, ranging from 1 cm to 1.8 cm in 0.2-cm steps, and depending on five measurements at each step: peak and mean gradients, peak velocity, effective orifice area, and indexed effective orifice area.
“Validation of candidacy for Melody MVR and noninvasive assessment among larger series of patient will be necessary as greater experience with the Melody valve evolves,” Dr. Freud and her associates concluded.
Coauthor Sitaram Emani, MD, has filed a patent for an expandable valve through Boston Children’s Hospital. Dr. Freud and her other coauthors had no financial relationships to disclose.
