Basics

The tricuspid valve is absent. The nearby inflow portion of the right ventricle is hypoplastic.

An ASD is always present to allow blood to leave the right atrium to enter the left atrium. There is usually a VSD for return of flow to the right side. In cases without VSD, there will be left to right flow through a ductus.

Classification

The great arteries are normally related in 70% and are transposed in 30%. The normal great artery relation type has 50% having restrictive VSD and PS, 10% having large VSD and no PS and 10% having intact ventricular septum and pulmonary atresia. The transposed great artery group has 20% having no PS, 8% having PS and 2% having pulmonary atresia. (Draw the connections yourself for a better idea.)

In the transposed great artery group, there will mostly be a VSD. Patients without a large VSD develop decreased aortic flow and shock.

Coarctation of aorta is the commonest associated anomaly. It is more common in patients with transposed great arteries.

Physiology

We can divide the patients into three groups- decreased pulmonary blood flow group, increased pulmonary blood flow group and balanced pulmonary blood flow group. The decreased pulmonary blood flow group is the largest and consists of NRGA+small VSD+PS, NRGA+ intact IVS+ pulmonary atresia, TGA + PS and TGA + pulmonary atresia groups. The increased pulmonary blood flow group consists of NRGA + large VSD + no PS and TGA + no PS groups.

The decreased pulmonary blood flow group has poor blood oxygenation leading to cyanosis and death. The increased pulmonary blood flow group does not have deep cyanosis, but has heart failure initially as the increased pulmonary blood flow will further overload the already overloaded left ventricle and then pulmonary vascular disease.

Some patients have pulmonary blood flow just enough to avoid deep cyanosis and not enough to cause heart failure or pulmonary vascular disease. These form the balanced pulmonary blood flow group.

Clinical and lab findings

Cyanosis is always present as the right sided blood always has to mix with left sided blood.

S2 is usually single as most patients have decreased pulmonary blood flow.

ECG shows right or biatrial hypertrophy. LVH is present. There will be left axis deviation.

Chest X-ray also shows right atrial enlargement and left ventricular enlargement.

Treatment

The commonest group is having normally related great arteries and decreased pulmonary blood flow. Immediate relief is by PGE1 infusion to increase pulmonary blood flow. In cases in which the ASD is small, Rashkind procedure (balloon atrial septostomy) may be done. The surgery is connecting the venacavae to the pulmonary artery- this is called Fontan surgery. This cannot be done in the neonate as pulmonary vascular resistance is high in the neonate and so venous blood cannot go into the high pressure pulmonary circulation. So first, a subclavian artery is connected to a pulmonary artery by a side to side window- this is called Blalock-Taussig shunt. At 3 to 6 months, when we are sure that pulmonary pressure has fallen enough, we can proceed to direct venous blood to the pulmonary circulation. The BT shunt is taken down. But full Fontan would be a major shift in the hemodynamics. So we direct only SVC blood to the pulmonary circulation at this 3 to 6 month period. This is done by bidirectional Glenn shunt or hemi-Fontan surgery. At 1 to 2 years after this surgery, full Fontan surgery is done by connecting IVC blood also to the pulmonary artery.

For the increased pulmonary blood flow group also, the final pathway is BDG or hemi-Fontan at 3 to 6 months followed by Fontan after 1 to 2 years. But in the neonatal period, the increased pulmonary blood flow can cause heart failure and pulmonary vascular disease- so to decrease pulmonary blood flow, PA banding will be needed.

For the balanced pulmonary blood flow group, till BDG or hemi-Fontan is done at 3 to 6 months, no surgery is needed, but they need close observation to monitor for decrease in pulmonary flow due to decrease in size of the VSD.

For the TGA group with a restrictive VSD, the neonatal problem is decreased systemic flow. So, either the VSD has to be enlarged or the main pulmonary artery is connected to the aorta to give blood to the aorta with the branch pulmonary arteries being detached from the main pulmonary artery to be connected to the aorta, the aorta now receiving blood from both the VSD and the main pulmonary artery, thus maintaining adequate systemic flow. Fontan surgery is done later as in other cases.

Bidirectional Glenn surgery- this refers to end-to-side SVC to right pulmonary artery shunt. When converting this to Fontan, the IVC is connected to a tubular pathway created in the right atrium, the tubular pathway being connected to the SVC orifice.

In the hemi-Fontan surgery, a side to side connection is made between the SVC and adjacent right atrium (this part of the right atrium having been sealed off from the rest of the right atrium) and the main pulmonary artery. When converting this to Fontan, a lateral atrial tunnel is made to connect IVC to this area.

The Fontan surgery is usually done at around 2 years of age. It will be dangerous with a high pulmonary vascular resistance (>2 U/m2) or pulmonary artery pressure (mean > 18 mmHg). Distorted pulmonary arteries from previous shunt surgeries also increase  the risk. AV valve regurgitation also increases the risk. LVEF less than 60% and LVEDP more than 12 mm Hg are the other risk factors. Early complications are heart failure, low cardiac output, persistent pleural effusion due to high venous pressure, thrombosis in systemic venous pathways due to sluggish flow and acute liver dysfunction due to low cardiac output. Late complications are supraventricular arrhythmias, ascites, protein losing enteropathy which causes death and cyanosis due to venous pathway obstruction, intra-atrial baffle leakage or pulmonary AV fistula.