Discussion

Tricuspid atresia is a CHD in which there is no or, rarely, an imperforate right atrioventricular connection. In the usual forms of tricuspid atresia, there is a hypoplastic right ventricle in the presence of a ventricular septal defect. When the ventricular septum is intact, the pulmonary valve is usually atretic. Tricuspid atresia with absent pulmonary valve and intact ventricular septum is an extremely rare cardiac malformation, historically associated with a poor prognosis.^{Reference Marin-Garcia, Roca, Blieden, Lucas and Edwards1–Reference Litovsky, Choy and Park3} Only a few cases with successful surgical palliation have been reported in the literature.^{Reference Mori, Ando, Satomi, Nakazawa, Momma and Takao2, Reference Forrest, Bini and Wilkinson4, Reference Lato, Gembruch and Geipel6–Reference Kasahara, Aeba and Yozu8} The present case shows that this rare CHD can be safely palliated in a staged approach towards the Fontan operation.

One of the characteristic morphologic features of this malformation is severely hypertrophied ventricular septum bulging into the left ventricular outflow tract (asymmetrical ventricular septal hypertrophy), which was also evident in our case.^{Reference Marin-Garcia, Roca, Blieden, Lucas and Edwards1–Reference Best, Vyas, Jaquiss and Sachdeva7} This can contribute to the development of left ventricular outflow tract obstruction, which is hazardous for single ventricle physiology. In our case, left ventricular outflow tract obstruction became obvious after the operation, probably due to volume-unloading nature of the bidirectional cavopulmonary anastomosis and dynamic left ventricular wall motion. Although the left ventricular outflow tract obstruction improved to mild degree at the time of discharge, judicious follow-up is mandatory for successful Fontan operation. Best et al reported “prophylactic” decompression of the right ventricle at the time of bidirectional cavopulmonary anastomosis by creating a ventricular septal defect to prevent the possibility of a hypertensive right ventricle bulging into the left ventricular outflow tract.^{Reference Best, Vyas, Jaquiss and Sachdeva7} Another characteristic morphologic feature of this malformation is the right ventricular dysplasia, in which large segments of the right ventricular myocardium are replaced with sinusoids and fibroelastic tissue.^{Reference Mori, Ando, Satomi, Nakazawa, Momma and Takao2, Reference Litovsky, Choy and Park3, Reference Lopes, Mennes, Delazoide, Iserin and Azancot5–Reference Kasahara, Aeba and Yozu8} This can cause variable degree of myocardial thinning and even aneurysmal change. A case with overt coronary-to-right ventricular fistulas has also been reported.^{Reference Kasahara, Aeba and Yozu8}

Surgical management of the non-functional right ventricle in this malformation is controversial due to the rarity of this condition. Leaving the main pulmonary artery untouched and connected to the right ventricle is the simplest option, although this may cause suboptimal cavopulmonary circulation due to to-and-fro flow between the right ventricle and the pulmonary artery. Complete exclusion of the right ventricle at the time of bidirectional cavopulmonary anastomosis, as was performed in our case, is another option. However, there are concerns regarding the hazardous effects of the potentially hypertensive right ventricle on the left ventricle after complete exclusion of the right ventricle.^{Reference Best, Vyas, Jaquiss and Sachdeva7, Reference Kasahara, Aeba and Yozu8} Kasahara et al reported fenestrated exclusion of the right ventricle in a patient with this malformation and coronary-to-right ventricular fistulas.^{Reference Kasahara, Aeba and Yozu8} We believe that, in the absence of significant coronary-to-right ventricular fistulas, complete exclusion of the right ventricle can be safely performed in this malformation.

In summary, tricuspid atresia with absent pulmonary valve and intact ventricular septum is an extremely rare cardiac malformation. Although this was associated with a poor prognosis in the past, it can be safely palliated in a staged approach towards the Fontan operation in the present day. Surgical management of the non-functional right ventricle in this malformation may differ depending on the presence and severity of the coronary-to-right ventricular fistulas.