ANOMALOUS PULMONARY VENOUS CONNECTION
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| TOTAL ANOMALOUS PULMONARY VENOUS CONNECTION |
In patients with anomalous pulmonary venous connection (APVC), all or some of the pulmonary veins fail to communicate with the left atrium, instead discharging blood into major systemic veins or directly into the right atrium. This discussion only considers the isolated forms of APVC. When these occur with other cardiac malformations, the clinical and hemodynamic features are usually modified or are chiefly determined by the complicating defect.
In partial anomalous pulmonary
venous connection, one or more pulmonary veins empty into the proximal SVC
close to the right atrium or into the sinus portion or the right atrium itself.
The involved veins almost always drain all or part of the right lung; the
others empty normally into the left atrium. An atrial septal defect (ASD) is
generally present, especially the sinus venosus type. The clinical
picture closely resembles that seen in other forms of ASD and is not discussed
here.
Total Anomalous Pulmonary Venous Connection
In total anomalous pulmonary venous
connection (TAPVC), all the pulmonary venous blood enters the systemic venous
system or the right atrium. An ASD or patent foramen ovale is always present.
Types of TAPVC are distinguished by how the pulmonary venous blood enters the
systemic circuit (see Plate 5-3).
Embryologically, the intrapulmonary veins are derived from the venous plexus
around the foregut and anastomose freely with the systemic veins early in the
embryo. After the embryonic main pulmonary vein has appeared as an outgrowth of
the primitive left atrium and established connections with the pulmonary venous
plexus, the systemic and pulmonary venous anastomotic channels typically are
obliterated. If the embryonic pulmonary vein does not develop at all or is
obliterated secondarily, some of the anastomotic channels are retained,
resulting in TAPVC.
TAPVC to Left Superior Vena Cava
By far the most common form of TAPVC
is that to a persistent left superior vena cava, illustrated as seen
from behind in Plate
5-3. The right pulmonary veins
con- verge to form a single vessel, which runs behind the small left atrium to
join the left pulmonary veins. From the junction of the pulmonary veins, a
large single vessel representing a persistence of the distal left SVC carries
the pulmonary venous blood by way of a dilated left brachiocephalic
(innominate) vein and the right SVC to the right atrium. An ASD, or more
frequently a widely patent foramen ovale, allows part of the right atrial blood
to enter the left atrium. Tremendous right atrial and right ventricular
enlargement develops early and rapidly.
Symptoms of persistent left SVC
generally appear shortly after birth, initially rapid respirations followed by
dyspnea, feeding difficulties, failure to thrive, and frequent respiratory
infections. As a rule, the patient has no obvious cyanosis, at least at first,
reflecting the mixing of a large amount of oxygenated pulmonary venous blood
with a much smaller amount of systemic venous blood. Cyanosis becomes more
pronounced if bronchopneumonia or congestive heart failure is present. Failure
almost always appears within the first 6 months of life, and the great majority
of these infants die during their first year. For unknown reasons, a small number of patients improve, a few of whom may
reach adulthood.
Cyanosis and clubbing of the digits
are common only in older children and adults with TAPVC. The heart is enlarged.
Generally there is no thrill, but a lower left parasternal “heave” is usually
present. A systolic murmur of mild to moderate intensity is present at the left
upper sternal border or sometimes lower. The pulmonic second sound is usually
loud and often split. A diastolic tricuspid flow murmur may be present along the right lower sternal border or over the
xiphoid process.
The chest radiograph features of
persistent left SVC in older children and adults are characteristic. The
dilated left and right superior venae cavae cause a rounded shadow in the upper
mediastinum. Together with the rounded and enlarged heart shadow, a typical
figure-eight or “snowman” appearance
is created. The pulmonary vascularity is greatly increased. The ECG shows
right-axis deviation and severe right atrial and right ventricular hypertrophy.
At cardiac catheterization, the oxygen content of the right SVC blood is found
to be very high, indicating a massive left-to-right (L →
R) supracardiac shunt, and the blood oxygen content is almost uniform in all
cardiac chambers.
The diagnosis of TAPVC to the left
SVC can be confirmed easily by selective injection of a contrast medium into
the pulmonary trunk. After passage of the contrast through the lungs, the
anomalous veins opacify quite satisfactorily. Computed tomographic angiography
(CTA) and cardiac MRI can also define the anatomic pathology of persistent left
SVC.
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| SURGERY FOR ANOMALOUS PULMONARY VENOUS RETURN |
TAPVC to Coronary Sinus
The pulmonary veins join to form a
very short, wide, common vessel that empties into the hugely dilated coronary
sinus in TAPVC to the coronary sinus (see Plate 5-3). The clinical picture and
ECG findings are similar to those just described for left SVC. The radiographic
appearance is different, in that the upper mediastinum is not widened. The
right atrium may be huge. Cardiomegaly and plethora of the lung fields are
seen. Cardiac catheterization fails to show the high oxygen content of the SVC;
otherwise, radiograph findings are similar to those in TAPVC to the left SVC.
Angiocardiography is much less helpful, and the anomalous connection to the
coronary sinus may be difficult to demonstrate with certainty. CT and MRI help
define the anatomic pathology.
Other types of TAPVC (e.g., to right
atrium or to several different sites) are infrequently seen as isolated
malformations, but also may be seen in association with other severe cardiac
defects.
Infradiaphragmatic Type
In an unusual form of TAPVC,
generally occurring as an isolated anomaly, the pulmonary veins drain into the
portal venous system. This is generally referred to as infradiaphragmatic TAPVC;
the other TAPVCs are classified as supradiaphragmatic. With
infradiaphragmatic TAPVC the pulmonary veins join to form a single long vessel
that descends in front of the esophagus and courses with it through the
esophageal hiatus, to enter the proximal portal venous system, generally the
left gastric vein. Usually, there is a stenotic area in the preesophageal vein
just before it enters the portal venous bed. Along with the need for pulmonary
venous blood to traverse the hepatic capillary bed before entering the right
atrium by the hepatic veins, this stenosis causes severe pulmonary venous hypertension
and is responsible for the characteristic clinical picture and laboratory
findings, which are quite different from those seen in the various
supradiaphragmatic TAPVCs. Plate 5-3 shows the infradiaphragmatic anomaly as
seen from the back.
Severe symptoms appear soon after
birth, and almost all infants with infradiaphragmatic TAPVC die within a few
days or weeks. The symptoms include clear persistent cyanosis, marked dyspnea,
and serious feeding difficulties. Cardiac failure becomes evident very early
and is almost impossible to treat successfully. These infants are obviously
very sick but show no abnormal cardiac findings. The heart is not enlarged, and
a murmur, if present, is faint. The ECG is normal or near-normal. The chest
radiograph is characteristic but not pathognomonic, since it is also seen in
other anomalies in which pulmonary venous obstruction
occurs. There is evidence of severe pulmonary venous hypertension: The hilar
markings are pronounced and fuzzy, and the lungs show a reticulated appearance.
Surgical Treatment
The treatment of TAPVC is surgical, to redirect pulmonary vein flow entirely to the left atrium (see Plate 5-4). In most types of total anomalous pulmonary venous return, the pulmonary veins return to a common confluence behind the left atrium. The common pulmonary vein confluence is connected to the back of the left atrium, resulting in a normal connection of pulmonary veins to left atrium. All other pulmonary vessels to the supracardiac or infracardiac areas are tied off. Any coexisting ASD is closed. Older children and adults generally have good surgical results. The repair results in normal circulation; the pulmonary veins return as normal to the left atrium, without abnormal connections or septal defects.
