Invited Commentary: A Lesson From Japan: The Art of Repairing the Infant Mitral Valve

In this issue of World Journal for Pediatric and Congenital Heart Surgery, Maeda et al. report excellent results in mitral valve repair for regurgitation in 18 consecutive infants operated on at their institution in Hyogo, Japan from 2005 to 2019. There were no early deaths and only 1 late death with a median follow-up of 7 years and 9 months. At both 5 and 10 years, they had survival of 94.4%, freedom from reoperation of 83.0%, freedom from valve replacement of 88.9%, and freedom from recurrent significant mitral regurgitation of 83.3%. These outcomes are better than those recently reported by Geoffrion et al. particularly the reintervention-free survival which in Dallas, Texas was 73.3% and 48.9% at 5 and 10 years. Similarly in the paper by Isaacson et al. comparing infant and child outcomes in Wisconsin, the 5-year survival (death/transplant free) was 78%, freedom from reoperation 72%, and mitral valve disease recurrence 47%, respectively. Of note, in these 2 papers from the United States centers, there were no infants with acquired mitral regurgitation, and congenital mitral stenosis (either mixed or isolated) featured in at least a third of their cohorts. Geoffrion’s paper compared outcomes in those with primary mitral stenosis versus mitral regurgitation and found no difference, although numbers were small. Maeda and associates stipulate in the discussion that their institutional preference is to perform the Norwood procedure in those with significant mitral stenosis presenting in infancy. Hence, those patients do not feature in this Japanese series, so perhaps this selectivity contributes to the better late outcomes. Looking closely at this group of 18 infants, not only are the congenital patients all pure mitral regurgitation, but 10 of the patients have acquired, acute pathology. For many of us working outside of Asia, the condition of acute mitral chordal rupture has never been encountered, but in Japan where it was first described by Mishima et al. in 1996, it is now a well-known entity. Matsumoto et al. in 1999, wrote up a series of 16 children describing how to repair the regurgitant mitral valve by reconstructing artificial chordae tendineae including 1 infant. He included a useful diagram of the technique, with reported outcomes at a median follow-up of 14.8 months showing no valve failures and 100% survival, which are outstanding for both congenital and acquired cases. A nationwide survey in Japan reported by Shiraishi et al. in 2014 documents 95 children having acute rupture of mitral chordae with 85% of them being between 4 and 6 months of age. Although 10 were caused by Kawasaki disease and 2 by maternally derived SSA antibodies, the majority had no formal etiologic diagnosis. In the 28 who had histologic evaluation, there were acute inflammatory reactions in some, and fibrosis or myxoid changes in others. They also report an 8.4% mortality in patients prior to getting to the operating theatre and persistent neurologic complications in 11% of survivors. This explains why Maeda describes these infants being operated on within 24 h of admission, with 9 of the 10 being on mechanical ventilation prior to surgery. The damage to coronary arteries in some patients with Kawasaki disease is well known but many patients also have mild mitral regurgitation (63% in a Japanese survey and 71% in a Chinese survey). It affects other valves too, and tends to resolve over the following year. Macrophages and cytotoxic T cells were reported to have invaded mitral tissue in 1 infant operated on a year after the initial diagnosis. These histopathologic findings, and the link with ethnicity, remind us of rheumatic valve disease, a far more common global cause of acquired mitral regurgitation in children, which is triggered by an immune reaction that activates T cells and is now demonstrated to correlate with certain genes that code for the proteins which mediate the immune responses. Histologic examination of any tissue removed at these acute infant operations may improve our understanding of the causative factors. Apart from the Japanese publications, there appears to be just 1 abstract describing mitral valve repairs in infants in China in 2017 in which 22 patients or 55% were under a year of age and their reported early outcomes were good. Yoshizawa et al. from Hyogo published in the WJPCHS the first paper that selectively reports on a group of infants with acute mitral chordal rupture. There is a detailed description of the typical presentation and the use of polytetrofluoroethylene chordal implantation, edge-to-edge suture, and Kay annuloplasty. They stress the need for prompt transfer to theatre and for 48 h of sedation afterward to avoid hypertension in the early phase postoperatively. These 6 cases, now included in the current paper, have no doubt enabled the surgeons to gain confidence in constructing chords at the correct length, even in these small infant hearts; however, this technique was not applied to their congenital infant cases. The concern that the use of polytetrofluoroethylene chord in an infant may impact the durability of the repair that has been addressed by Sai et al. in their careful echo follow-up of 8 infants aged 1 to 7 months over a mean of 5.8 years. Freedom from reoperation is 100% and any postoperative mitral regurgitation tended to improve with time, with an left ventricular end diastolic dimension that remained normal over 5 years. They measured the length of the associated papillary muscle and showed that it grows in length as expected and correlates with body surface area. Isaacson et al. in his description of the index procedures for congenital mitral repair, does not use chordal insertion in infants and Geoffrion reports only 1 in their 25 infants. This Japanese report demonstrating the safety of polytetrofluoroethylene chordal insertion in infants should encourage us to use this technique in the congenital infants and children we encounter with more confidence in its durability. We can also be prepared, just in case, in this global community we now live in, we one day encounter an infant case of acute acquired mitral regurgitation.