Tricuspid Atresia
Tricuspid atresia (TA) implies complete agenesis of the tricuspid valve with loss of
continuity between right atrium and right ventricle. Several associated cardiovascular
malformations must be present for this lesion to be compatible with life: an atrial
communication (ASD or PFO) must be present for systemic venous return to cross to the left
atrium and be pumped from the left ventricle.
Relative or absolute hypoplasia of the right ventricle is an obvious consequence of the
loss of direct AV connection. This can vary considerably, however, depending on the
presence of a ventricular septal defect (VSD). A VSD will allow for entry of blood into the
right ventricle and the pulmonary artery. If a VSD does not exist, the ventricle receives
no flow and will be extremely small, with hypoplasia or atresia of the pulmonary valve and
trunk. The echo shown on the left is a '4 chamber view' of a newborn with TA, a VSD and a
small RV.
If the ventricular septum is intact, a separate systemic arterial-to-pulmonary source is
required such as a PDA or an aorto-pulmonary collateral vessel.
CLINICAL CONSIDERATIONS Tricuspid Atresia may be associated with other congenital cardiac
anomalies. Most notably, 12-23% of patients will have d-transposition of the great arteries
(d-TGA). D-TGA patients may have coarctation or hypoplasia of the aortic arch as an
additional finding depending on the size of the VSD and its resultant flow into the RV.
Cyanosis with a murmur in the neonatal period is the most frequent presentation. Cyanosis
is most severe with an intact ventricular septum or pulmonic stenosis. Hypercyanotic spells
such as those seen with Tetralogy of Fallot can occur, usually in young infants. The
cyanosis is least severe with a large VSD or with d-TGA and unrestricted pulmonary blood
flow. The infant will still have complete venous mixing at the atrial level, but the
symptoms of pulmonary overcirculation and congestive heart failure will dominate the
clinical picture. Hypoplasia or coarctation of the aortic arch associated with d-TGA and TA
can result in systemic perfusion and shock as the PDA closes. Ductal patency must be
maintained with intravenous prostaglandins until surgical palliation. Rarely, the atrial
shunt will be restrictive in size. This will decrease cardiac output and cause poor
perfusion. In this setting an urgent atrial septostomy is indicated to ensure right atrial
decompression.
Chest Xray appearance is variable depending on the amount of pulmonary blood flow.
Diminished pulmonary blood flow is seen with normal or slightly enlarged cardiac
silhouette, concavity in the pulmonic area and decreased pulmonary vascular markings.
Increased blood flow will be associated with cardiac enlargement and pulmonary congestion.
ECG findings with TA are very specific. Most other cyanotic heart lesions present with
increased right-sided forces, i.e. right axis deviation and right ventricular hypertrophy.
With the hypoplastic right ventricle of TA, right-sided forces are diminutive or even
absent. The ECG will show a left and superior axis in nearly 90% of TA with normally
related great arteries, and 50% with d-TGA will also be 0 to Ð90 degrees. The rest should
fall in the left inferior quadrant, still more left than would otherwise be expected for a
cyanotic newborn.
Echocardiography confirms the diagnosis. Ventricular size, atrial and ventricular shunts,
location and function of the AV valves, and relationship of the great arteries are all well
seen with echocardiography. Presence of a left SVC and its atrial communication can also be
established, which is of importance to the surgical repair.
Treatment is surgical. Children less than 6 months of age with diminished pulmonary blood
flow will require a systemic shunt. The modified Blalock-Taussig shunt is associated with
the lowest incidence of pulmonary overcirculation and the least deformation of the
pulmonary arterial tree. Infants with increased pulmonary blood flow may require pulmonary
artery banding until they have reached an appropriate size to proceed with their
palliation.
Definitive palliation is achieved through a staged procedure to create complete
cavo-pulmonary continuity that bypasses the right ventricle. The bidirectional Glenn shunt
is the preferred SVC to PA anastomosis with completion of the Fontan when the child is of
the appropriate size.
Transesophageal echo shows the VSD in center screen connecting to the RV and
the failed development of the tricuspid valve on screen left. The mitral valve opens freely
in mid-screen.
Subcostal echo view shows the absent tricuspid valve with a rudimentary
right ventricle. The ASD (marked) permitted RA -> LA flow during fetal development.