Discussion:
The clinical findings associated with the occurrence of a direct fistula
between the right pulmonary artery and the left atrium. Furthermore, it
was vary from mild to extreme cyanosis with clubbing and exertional
dyspnea. These patients with above-mentioned symptoms may experience
increased blood viscosity, due to the high hemoglobin levels caused by
chronic hypoxia. In addition to this, bypassing of the pulmonary
vascular bed, the blood filtering function of the lung is lost, which
leads to complications such as emboli, brain abscesses, cerebrovascular
events and other systemic embolic events (6), one of the rare
complications that may occur is fistula rupture.
De Silva et al. (8) described three patterns of fistula between the
pulmonary artery and the left atrium depending on where the fistula
opened on the left atrium and its relationship with the branches of the
right pulmonary artery and pulmonary veins.
Type 1 : The right pulmonary artery and its branches and the
pulmonary veins are normal but there is a fistula between the right
pulmonary artery and the
left atrium.
Type 2: The lower right pulmonary vein is absent and the lower
branch of the right pulmonary artery drains directly to the left atrium
where the lower right pulmonary vein usually opens into the atrium.
Type 3: Pulmonary veins drain to an abnormal duct between the
left atrium and the right pulmonary artery (a fistula).
Later, the fourth type was added by Oahu et al. 1979 (9). This pattern
is similar to the second pattern, where the right pulmonary veins enter
the fistula that resembles an aneurysm and connects the lower branch of
the right pulmonary vein with the left atrium Fig 4)
In the case we present here, the right pulmonary artery which supplies
the middle pulmonary lobe drains directly into the left atrium through a
large fistula taking the form of an aneurysm where the upper right
pulmonary vein usually drains into the atrium. This case doesn’t fall
under any particular classification but is somewhat similar to Type-2.
(Fig. 5)
There is no definite fetal origin or explanation for the fistula between
the right pulmonary artery and the left atrium; some theories suggest
the presence of a connection between the right pulmonary artery and the
primary pulmonary vein. At a later stage, the primary pulmonary vein
merges into the atrial wall resulting in the fistula (10, 11). Atrial
septal defect is the most common cardiac defect associated with the
fistula between the right pulmonary artery and the left atrium, the
absence of the lower pulmonary lobe and right bronchial atresia are the
most common pulmonary malformations (12, 13).
In this case, we found only an ASD of a 6.5 mm diameter that was closed
at the surgical repair of the fistula. When diagnosed, this condition
should be treated with selective surgery to close the fistula (14). This
can be achieved either through outside ligation without cardiopulmonary
bypass, or through open heart surgery using a patch which was performed
in the case we presented. The surgical approach was selected due the
presence of the ASD and the size of the fistula and the thinness of its
wall causing concern of rupture. Many other cases were mentioned in the
medical literature regarding the closure of the fistula using cardiac
catheterization which is an effective alternative to surgical closure.