Glenn shunt is a surgical procedure done for children who are born with cyanotic heart disease ("blue babies"), in which a large vein, the superior vena cava is joined to the right pulmonary artery so that blood goes around the deformed right chambers of the heart and is shunted directly into the lungs to be oxygenated. Generally, this procedure is done when the right ventricle or left ventricle is much smaller than normal or impaired in other ways and is not capable to sufficiently pump blood to the body or lungs. Glenn Shunt is one of the more well-known operations used by Congenital Cardiac surgeons. It is also known as the Glenn Procedure. “Shunt” means “detour”. Glenn shunt surgery is habitually part of the staging that results in a very victorious palliative surgery named ‘Fontan’. The Glenn fell out of favor after the Fontan Procedure was introduced. Subsequent to years of abandon, glenn shunt was looked at again when the early versions of the Fontan did not convey the expected results. Glenn shunt had originated into the ‘Bidirectional Glenn Shunt’ (BDG), by then. Now, the Bidirectional Glenn Shunt can be used as an option to repair most of the right-sided heart defects.
Glenn shunt was discovered by William W. L. Glenn (1914-2003), who was a chief of cardiovascular surgery at Yale University.
Glenn shunt is an open heart procedure, often using the heart lung bypass machine and involves connecting the superior vena cava (which returns un-oxygenated blood from the head and upper body to the lungs) to the right pulmonary artery, as a result carrying the blood straight to the lungs for oxygenation without going through the heart. This boost up the blood flow to the lungs and reduces the work of the heart. It will not work where there is pulmonary hypertension as the blood has to flow without the force of the heart pumping. Occasionally, Glenn is referred to as the Modified or Bi-Directional Glenn Shunt as the procedure performed these days is a modified form of the original operation and it now supplies blood to both lungs, hence bi-directional. The Glenn is usually one in a series of operations, done after the removal of a BT Shunt, or pulmonary artery banding.
The Fontan procedure is a surgical procedure used in children with multifaceted congenital heart defects. A congenital heart defect (CHD) is a defect in the structure of the heart and great vessels which is present at birth. It involves redirecting the venous blood from the right atrium to the pulmonary arteries without passing through the morphologic pulmonary ventricle. In recent times, the Fontan procedure has more been used in medical conditions where an infant only has a single effective ventricle, either due to heart valve defects or an irregularity of the pumping ability of the heart, or has complex congenital heart disease where a bi-ventricular repair is unfeasible or not recommended. It is designed to direct the blood coming back from the body directly to the lungs, without it being pumped there by the heart. A lot of patients would have had a bidirectional Glenn shunt, in the past. The Fontan is an open heart procedure during which the unoxygenated blood returning from the lower part of the body is diverted directly to the pulmonary (lung) artery without passing through the right ventricle. This may be accomplished in various ways all of which connect the inferior vena cava directly to the lung artery, allowing the de-oxygenated blood flow to the lungs while the ventricle pumps the oxygenated blood to the body. The procedure depends on blood flowing to the lungs without the advantage of a pump so it is not appropriate for patients with pulmonary hypertension (high lung artery pressure).
Even though, a bidirectional Glenn (BDG) shunt is not accurately a Fontan operation, it is comparable to it. It is known as a kind of "Partial Fontan" operation. It is also known as ‘Bidirectional Cavo-Pulmonary Shunt (BCPS)’.
The BDG procedure is the surgery which is used to prepare the heart for a Fontan procedure. The operation is done as follows:
The bidirectional Glenn shunt is favored in infants, below 2 years of age, for whom the lung vessel resistance is pretty high, and in intermediate cases with abnormal pulmonary arteries. It is common for children to undergo this surgery in the first three to six months of life, and it drastically improves results for most. Though evading the risk of failure of a complete Fontan operation, it also to a certain extent relieves symptoms. If all is well after the Glenn shunt, and the lung vessel resistance is low, a change to total Fontan is likely. If not, it is not possible to do anything. Bidirectional Glenn shunt surgery is an excellent method for continuing to support life than early shunt procedures like the Blalock-Taussig (BT) Shunt or the Norwood, that children with single ventricle might obtain in the early days of life.
While improving oxygen saturation, BDG reduces volume load on the single ventricle as compared to the pre-operative condition.