Tricuspid atresia
Tricuspid atresia is a rare congenital heart defect with an estimated prevalence of 1 in 15.000 live births47. This lesion was first described by Friedrich Ludwig Kreysig in 1817 and is characterized by an absence of the tricuspid valve, resulting in complete obstruction of blood flow between the right atrium and right ventricle48. From a pathophysiologic perspective, the inflow portion of the RV (normally directly related to proper development of the TV) is absent. Consequently, there is an obligatory right-to-left shunt at the atrial level, and a communication between the systemic and the pulmonary circulation is enabled by a perimembranous (or rarely muscular) ventricular septal defect (VSD). In the presence of a large VSD, cardiac remodeling of the trabecular portion is usually less severe, resulting in a larger RV. In those rare cases of TA with an intact ventricular septum, the corresponding ventriculoarterial connection is atretic, and the RV is nonfunctioning and severely hypoplastic49. TA is frequently associated with other intracardiac anomalies that dictate the clinical presentation pre- and postnatally. According to the nature of the ventriculoarterial connection, TA has been initially classified into three groups (type I-III); these groups were subsequently modified taking into account the presence and degree of right ventricular outflow tract obstruction50,51.
Prenatal diagnosis of TA is usually straightforward, with a high accuracy. Berg et al. noted 46 % discordant ventriculoarterial connections in their cohort. Similar findings were reported in a previous study conducted by Wald and colleagues52. Both cases reviewed herein had an atretic TV and ventricular asymmetry but normally arranged great vessels (figure 3 a,b) on 2D ultrasound. Doppler interrogation showed no blood flow velocities across the TV. Volume acquisition and subsequent FINE application was performed at 22 gestational weeks in each case and showed an abnormal 4CV with a thickened fibrous plate instead of a competent tricuspid valve. The RV was reduced in size but contractile. The remaining axial planes displayed fundamental differences between both cases. Whereas the ascending aorta in the three-vessel-trachea (3VT) view was s-shaped, the main pulmonary artery was stenotic (figure 3a). The left-sided structures appeared otherwise normal. Pulmonary forward blood flow was maintained through a perimembranous VSD (seen in the 4CV and LVOT views) and a large interatrial communication. The RVOT plane showed a normal branching of the main pulmonary artery. These anatomic changes are referred to as TA type Ib. Notably, the fetus in figure 3b had a completely different hemodynamic situation. In the 3VT view, there was only one outlet vessel (ascending aorta), and the 4CV view showed a rudimentary RV and an enlarged LA. In addition, the fetus had a restrictive foramen ovale and no communication at the ventricular level. The pulmonary artery was atretic (seen in the RVOT and ductal arch views), corresponding to TA type Ia.
In both studies cited above, the overall survival of pregnancies continued until term was approximately >80 %. The individual prognosis of TA diagnosed in utero was likely to be determined by the presence of associated chromosomal anomalies or syndromes that accompany TA in significant proportion of cases49,52. Berg et al. highlighted the need for close surveillance in the third trimester to rule out interatrial restriction and stated that frequently seen DV changes in TA do not indicate cardiac compromise and are rather related to the changes in hemodynamics in affected fetuses49. On the other hand, according to a recent study, an increased peak velocity index of the DV can be used to predict compromise in fetuses with obstructive right heart lesions53.