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.