Discussion

Isolated tricuspid regurgitation had no displacement of the tricuspid valve and thus no atrialised ventricle, which was quite different from Ebstein’s diseases.^{Reference Aaron, Mills and Lower6} Children were so rare that there were only few cases reported.^{Reference Jaquiss and Imamura3–Reference Seguela, Roubertie, Tafer, Thambo and Iriart5,Reference Katogi, Aeba, Ito, Goto, Cho, Ueda and Kawada8,Reference Lim, Huh and Jun12,Reference Mizuno, Hoashi and Sakaguchi14} About 43,000 children diagnosed with CHD underwent cardiac surgery in Fuwai hospital from January, 2010 to December, 2019. However, only 10 consecutive patients with isolated tricuspid regurgitation underwent tricuspid valve repair surgery. Thus, the prevalence was estimated at 10 in 43,000 (0.023%) of CHD population. It was generally acknowledged that isolated tricuspid regurgitation can be well tolerated, and even one patient without clinical symptoms for 32 years.^{Reference Morgan and Forker7,Reference Beckhoff, Alushi and Jung15} But not all children responded well to drug therapy and some patients died from chronic cardiac failure or pneumonia in previous reports.^{Reference Aaron, Mills and Lower6} Thus, some patients require timely surgical intervention, repair, or replacement. Tricuspid valve replacement in children was a procedure with a high risk of early post-operative death. Heather et al^{Reference Bartlett, Atkins and Burns16} reported 97 cases of tricuspid valve replacement in children <6 years of age from 1984 to 2002, that 26 patients (27%) did not survive to discharge (n = 24) or required cardiac transplantation before discharge (n = 2, considered failures for analysis) after tricuspid valve replacement. Although 35 patients surviving to discharge with further data available, 13 (37%) patients were known to have died or undergone cardiac transplantation. Hence, we believed that tricuspid valvuloplasty was the best choice for children with the advantages of avoiding anticoagulation and good growth potential. As described in the article, tricuspid valvuloplasty was performed successfully in all of these patients and there was no patient underwent tricuspid valve replacement. As mitral repair, the principles of tricuspid valve reconstruction were restoration of full leaflet mobility, correction of prolapse, provision of a large leaflet coaptation surface, and annular stabilisation.^{Reference Antunes, Rodriguez-Palomares and Prendergast17} This study demonstrated our experiences of tricuspid valvuloplasty for severe isolated tricuspid regurgitation in children.

There were various pathological lesions may lead to severe tricuspid regurgitation. As explained in our study, major causes for isolated tricuspid regurgitation in paediatrics included congenital leaflet dysplasia and abnormal sub-valvular structure, especially leaflet cleft and abnormal chordae tendineae. Most of the patients were clearly diagnosed in the neonatal period for cyanosis and need surgical repair.^{Reference Katogi, Aeba, Ito, Goto, Cho, Ueda and Kawada8,Reference Lim, Huh and Jun12,Reference Sachdeva, Fiser, Morrow, Cava, Ghanayem and Jaquiss18} Besides, Morgan et al^{Reference Morgan and Forker7} confirmed that trauma can also lead to papillary muscle or chordae tendineae rupture, leading to severe tricuspid regurgitation.

Thirty per cent of patients in our cohort combined with chordae tendinea rupture, and it was believed to be congenital developmental abnormality on the basis of clinical history. To repair the ruptured chordae tendinea, insertion of an artificial tendinous cord or using 5/0 prolene suture to connect the ruptured chordae tendineae with papillary muscle was performed.^{Reference Katogi, Aeba, Ito, Goto, Cho, Ueda and Kawada8,Reference Lim, Huh and Jun12,Reference Sachdeva, Fiser, Morrow, Cava, Ghanayem and Jaquiss18} Toshiyuki et al reported their experience of artificial chordae implantation in a 15-year-old boy and recovered well after the operation.^{Reference Katogi, Aeba, Ito, Goto, Cho, Ueda and Kawada8} Rody et al agreed that tricuspid valve repair with artificial chordae in children demonstrated acceptable results and valvular restriction by the artificial chordae was not observed after mid-term follow-up.^{Reference Boon, Hazekamp and Hoohenkerk19} Jolanda et al reported their 15-year experience with the use of artificial chords for valve reconstruction in children, and they found that only 1 (6.7%) patient occurred leaflet motion restricted caused by artificial chords. Despite patients grew and developed over time, we agreed that restricted leaflet motion by the artificial chords did not seem to form a major problem.^{Reference Kluin, Sojak, Koolbergen, Boon, Bokenkamp and Hazekamp20}

Besides chordae tendinea rupture (3/10), there were 40% patients in our series diagnosed with abnormal chordae tendinea, including mal-connected chordal tendinea to leaflets (2/10), elongated chordae (1/10) and chordae absent (1/10), and severe anterior leaflet dysplasia (1/10).Tethering of the tricuspid valve leaflets by aberrant tendinous chords can be the sole mechanism of severe congenital tricuspid regurgitation.^{Reference Kobza, Kurz and Oechslin21} Aberrant tendinous chords connected to the tricuspid valve leaflets would limit the mobility of the tricuspid leaflet and resulted in incomplete coaptation and apical displacement of the regurgitant jet origin.^{Reference Kobza, Kurz and Oechslin21} Tricuspid structure should be carefully examined by echocardiography before surgery and distinguish it from other malformations involving tethering. In our experience, resection of the tethering chords could restore full mobility to the involved leaflet, which could reach the coaptation plane.

Leaflet clefts in tricuspid valve was a rare disorder with an incidence of 0.6% among patients with CHD.^{Reference Eichhorn, Suetsch, von Segesser, Turina and Jenni22} In another study, the prevalence was estimated in 5 of 28,091 (0.018%) Doppler echocardiograms. Many previous cases reported it was associated with patent foramen oval, atrial septal defect, peri-membranous ventricular septal defect, or pulmonary stenosis.^{Reference Seguela, Roubertie, Tafer, Thambo and Iriart5,Reference Eichhorn, Suetsch, von Segesser, Turina and Jenni22,Reference Motoyoshi, Tofukuji, Sakurai, Ohmi and Tabayashi23} The pathogenesis was still unknown. It may be associated with the development of the endocardial cushion.^{Reference Seguela, Roubertie, Tafer, Thambo and Iriart5} The diagnosis of tricuspid regurgitation can be established by echocardiography and then depicted the tricuspid valve morphology accurately.^{Reference Seguela, Roubertie, Tafer, Thambo and Iriart5,Reference Motoyoshi, Tofukuji, Sakurai, Ohmi and Tabayashi23} It was effective to control tricuspid regurgitation with only cleft closure and tricuspid annuloplasty in our patients, while Kosuke et al thought it was necessary to perform chordal reconstruction to stabilise the repair and prevent the recurrence of tricuspid regurgitation if the patient diagnosed with remarkably enlarged the anterior leaflet and elongated chordae tendineae.^{Reference Saku, Inoue, Yamamoto and Ueno24} For patients with severe tricuspid leaflet dysplasia or with inadequate leaflet area, the use of an autologous pericardial patch to enlarge the tricuspid leaflets could increase the surface of coaptation and allow good coaptation effectively at the level of the tethered anterior and posterior leaflets while maintaining leaflet mobility.^{Reference Dreyfus, Raja and John Chan25}

Surgical options were related to specific structural anomalies of leaflets, annulus, and sub-valvar structures. Recognition of tricuspid valve anatomy and precise definition of tricuspid lesion were essential to tailor a specific and appropriate repair surgery. In our experience, if patients with simple or single pathological lesion, such as leaflet cleft, mal-connected chordal tendinea to leaflets, or elongated chordae, they may get a good outcome after surgery. Complex or multiple tricuspid lesions, such as severe anterior leaflet dysplasia, chordae tendinea rupture, or chordae absent, on the contrary, may responsible for increased surgical difficulty and recurrent risk. Besides, the use of autologous pericardial patch to enlarge the tricuspid leaflets and insertion of an artificial tendinous cord may also add the risk of recurrence of valve regurgitation. Since our series were small, larger sample size and longer follow-up were needed.