ANOMALIES OF THE ATRIA
Juxtaposition Of The Atrial Appendages
In juxtaposition of the atrial appendages (auricles), the main bodies of the atria are normally located, but there is levoposition of the right atrial appendage. Instead of being to the right of the arterial trunks, the right atrial appendage crosses behind them to appear on their left, interposing itself between the great arteries and the left atrial appendage. Juxtaposition of the atrial appendages has no functional significance because it causes no hemodynamic disturbance itself. Its presence, however, always indicates the coexistence of other major cardiac anomalies. Transposition of the great vessels and a ventricular septal defect are invariably present, and atresia of the tricuspid valve is common. Plate 5-5 also depicts a double aortic arch.
In the rare cor triatriatum, a fibromuscular septum divides the
left atrium into a posterosuperior part receiving the pulmonary veins and an
anteroinferior part giving access to the mitral valve and left atrial appendage
(see Plate 5-5). Cor triatriatum is probably caused by
incomplete incorporation of the embryonic common pulmonary vein into the left
atrium. The original pulmonary venous ostium is represented by an opening of
variable size. Rarely, the septum is imperforate, and the distal pulmonary
venous compartment drains through a defect into the right atrium or an
anomalous vessel into the systemic venous system. Usually the fossa or foramen
ovale is located between the anteroinferior compartment and right atrium.
The severity of symptoms depends on
the size of the opening between the two compartments of the left atrium.
Respiratory difficulties and dyspnea may be marked, and cardiac failure
develops early. If the os is very small, death occurs within the first year of
life; if it is larger, symptoms appear later and closely resemble those seen in
mitral stenosis, i.e., chronic cough, dyspnea, fatigability, chest pain,
and hemoptysis. Cyanosis may be present, and there is marked cardiomegaly. A
mild or moderate systolic murmur is usually heard, but a diastolic murmur is
seldom present. The ECG usually suggests right ventricular hypertrophy because
the pulmonary pressure is elevated. Cor triatriatum is easily diagnosed with
transthoracic cardiac ultrasound and other imaging modalities. Surgical repair
is relatively simple; the anomalous membrane is excised.
Congenital absence of the spleen
rarely occurs alone. Other visceral anomalies are present in most patients,
about 60% of whom have the typical asplenia syndrome (see Plate 5-5). The most important feature of asplenia
syndrome is the tendency for normally asymmetric organs (e.g., liver, lungs) to
develop more or less symmetrically. The stomach may be located on either side
or rarely in the midline. Both lungs are usually trilobed and resemble a normal
right lung. The heart is generally severely malformed. A single or common
ventricle is usually present and an endocardial cushion defect of the complete
type often found. Transposition of the great vessels is the rule, usually
associated with pulmonary stenosis. The atrial
septum is reduced to a peculiar triangular band of muscle that crosses the
common atrioventricular orifice. In typical cases, both the right atrium and
the left atrium morphologically resemble a normal right atrium (isomerism of
atria), meaning that both sinus horns have been incorporated into their
corresponding atria. A coronary sinus is therefore absent. TAPVC is typically
present. The great systemic veins also tend to develop symmetrically, at times
with a bilateral SVC and a large vein entering on each side of the atrial
floor, representing a bilateral persistence
of the proximal vitelline veins. One of these drains a lobe of the liver
(common hepatic vein), and the other drains the opposite lobe and the remainder
of the IVC bed. The site of the viscera is impossible to determine (situs
ambiguus, or heterotaxy syndrome).
The diagnosis of asplenia syndrome
should be suspected in any infant with CHD associated with some form of partial
visceral heterotaxy, particularly if cyanosis is present. Howell-Jolly and
Heinz bodies are typically present in the peripheral blood smear. The prognosis is poor.
