What is the Fontan modification called the Bidirectional Glenn shunt ?
Although not exactly a Fontan operation, a bidirectional Glenn (BDG) shunt is similar to it - and is
called a type of "Partial Fontan" operation. It is also called Bidirectional Cavo-Pulmonary Shunt
(BCPS).
The bidirectional shunt is performed by connecting the superior vena cava (SVC) to the right
branch of the pulmonary artery using fine sutures, and dividing or tying up the pulmonary artery.
Now, venous blood from the head and upper limbs will pass directly to the lungs, bypassing the
right ventricle. The venous blood from the lower half of the body however will continue to enter the
heart.
At a second operation, the lower body venous blood will also be diverted to the lungs, thus
creating the "complete" Fontan circulation.
The bidirectional Glenn shunt is preferred in very small babies - below 2 years of age - in whom the
lung vessel resistance is still quite high, and in borderline cases with abnormal pulmonary arteries.
While avoiding the risk of failure of a complete Fontan operation, it also partly relieves symptoms.
If all is well after the Glenn shunt, and the lung vessel resistance is low, a change to complete
Fontan is possible. Otherwise, nothing further is done.
How is a BDG helpful ?
It decreases volume load on the single ventricle while improving oxygen saturation as compared to
the pre-operative state. In addition, by being a low-pressure shunt, it does not carry the risk of
causing lung blood vessel thickening and hardening.
To learn about the other modifications of a Fontan operation, read the next article in this series.
