What are the five T’s of Congenital Heart Disease? This must be one of the questions most of the persons reading this article faced during a viva exam some point in their studentship or career.

The most common cyanotic heart conditions presenting in the neonatal period are referred to as “The five T’s”
1. Tetralogy of Fallot (TOF)
2. Transposition of the Great Arteries (TGA)
3. Truncus Arteriosus
4. Tricuspid Atresia
5. Total Anomalous Pulmonary Venous Connection (TAPVC)

In addition, pulmonary atresia with and without a ventricular septal defect is a complex condition which often requires early surgical intervention. Each is briefly described below with its preferred therapeutic approach.

Tetralogy of Fallot
Tetralogy of Fallot is perhaps the best known of the cyanotic heart lesions. Of the four anomalies (overriding aorta, right ventricular hypertrophy, ventricular septal defect, and right ventricular outflow tract obstruction) only the latter two are of major physiologic consequence. The outflow obstruction usually occurs in the sub-valvar region (infundibulum), but may be at the level of the valve or in the pulmonary arteries. Cyanosis varies with the degree of outflow tract obstruction and the size of the ventricular septal defect. This lesion is often accompanied by hyper cyanotic episodes (Tet spells) which occur when systemic vascular resistance drops or right ventricular outflow obstruction increases. Right to left shunting through the ventricular septal defect causes cyanosis. Infundibular spasm is thought to play a role in initiation of Tet spells. Early repair is favored over palliation unless birth weight is low or if the patient’s condition is suboptimal. At surgery, the ventricular septal defect is closed with a patch, and any obstructing right ventricular muscle is removed. All other sites of outflow tract obstruction, including the valve and pulmonary arteries must also be addressed.

Transposition of the Great Arteries
Transposition of the Great Arteries is the most common cyanotic condition that requires hospitalization in the first two weeks of life. Anatomically, the aorta arises from the right ventricle and carriers deoxygenated blood to the systemic vasculature. The pulmonary artery arises from the left ventricular and carries oxygenated blood to the lungs. The only possibility for survival is to allow the two parallel circuits to mix. This is accomplished initially by augmenting ductal flow with PGE. The interatrial septum may be opened by balloon septostomy to further improve intracardiac mixing, and the patient is allowed to stabilize for a short period of time prior to definitive surgical correction. Although a number of repairs have been utilized for transposition, the most effective one is the arterial switch procedure. At surgery, the aorta and pulmonary artery are removed from their respective ventricles, and reattached to the correct ventricles. The coronary arteries are transferred separately to the newly reconstructed aorta. The procedure is technically challenging, but the results are gratifying. Experienced centers enjoy a 90-95% survival rate.

Truncus Arteriosus
Truncus arteriosus is a condition in which only one artery (the truncus) originates from the heart, supplying both the aorta and pulmonary artery. A ventricular septal defect is present just below the truncal valve which allows mixing of right and left ventricular blood. The degree of cyanosis is variable and depends on the pulmonary vascular resistance; and signs of progressive heart failure are prominent. Despite early medical management for heart failure (digoxin, diuretics), most patients require surgical repair at 2 to 3 months of age. At surgery, the ventricular septal defect is closed, and the pulmonary artery trunk is separated from the truncus. Continuity is then established between the right ventricle and the pulmonary artery utilizing a valved homograft conduit. This procedure restores the normal cardiac anatomy with greater than 90% survival. However, late complications can occur. The homograft valve may degenerate and calcify, becoming partially obstructive. The conduit may also become obstructed. The patient may outgrow the repair, thus requiring one or more repeat operations later in life.

Tricuspid Atresia
Tricuspid atresia occurs when the tricuspid valve fails to develop and there is no connection between right atrium and right ventricle. Desaturated venous blood returning to the right atrium must therefore cross though the patent foramen ovale to the left atrium and ventricle. The right ventricle is often hypoplastic, and therefore unusable in any subsequent repair. The philosophy of repairing tricuspid atresia and other “functional single ventricle” defects is to utilize the developed ventricle solely for systemic arterial flow, allowing venous return to flow passively to the lungs without the aid of a pumping chamber. The superior and inferior vena cavae are connected directly to the pulmonary arteries. Pulmonary blood flow is dependent upon very low pulmonary vascular resistance and is driven by elevated central venous pressure. Thus, these procedures cannot be performed in the neonatal period because the pulmonary vascular resistance is elevated. Initially, a systemic to pulmonary arterial shunt is required to increase pulmonary blood flow. Several months later, a superior caval to pulmonary artery connection (Glenn shunt) is performed and the initial shunt is ligated. The inferior caval connection may be done 12 to 18 months later (completion Fontan). Staging has helped to reduce morbidity and mortality in high-risk patients

Total Anomalous Pulmonary Venous Connection
With total anomalous pulmonary venous return the pulmonary veins are not attached to the left atrium, but converge in a common confluence just posterior to that atrium. This confluence drains into a systemic vein, or veins which may be obstructed. Obstruction to pulmonary venous flow causes pulmonary edema and decreased pulmonary arterial flow, resulting in cyanosis. These children are often extremely ill, with profound desaturation and acidosis. PGE1 administration does not improve oxygenation in this case because elevated pulmonary pressures in the right side of the heart (due to obstructed pulmonary outflow) will result in right to left shunting across an open ductus further decreasing arterial saturation. The only treatment for this condition is expeditious surgery. A surgical connection is made between the pulmonary venous confluence and the left atrium. The anomalous connection to the systemic venous circulation is then ligated. Mortality rates can be as high as 20% because of the critical condition of the children, but most patients do well.

Pulmonary Atresia
Pulmonary atresia is among the least common of the cyanotic congenital heart defects. Anatomically, there is no communication between the right ventricle and the pulmonary arteries, and abnormalities of the right ventricle and coronary arteries are common. Infants born with pulmonary atresia are dependent on the ductal arteriosus for pulmonary blood flow and therefore ductal patency must be maintained by PGE. Right ventricular pressures may be systemic if a large VSD is present, or supra-systemic with severe tricuspid regurgitation if no VSD is present. In some of these latter cases, right ventricular to coronary artery fistulae develop.

Early surgical intervention in neonates with pulmonary atresia is indicated in all cases. The goals of surgical intervention are to enhance pulmonary blood flow and promote right ventricular growth in cases of relative hypoplasia. The initial approach is palliative. In patients with a large ventricular septal defect and well-developed right ventricle, a systemic to pulmonary arterial shunt is usually sufficient. For those patients with a poorly developed right ventricle (and small or absent septal defect), restoring the pulmonary artery connection can decompress the high-pressure right ventricle, enhance its development, and minimize coronary fistulae. A shunt is also performed to further improve pulmonary blood flow. In these conditions, further reconstruction is usually required later in infancy. Survival is variable in this morphologically diverse group and depends largely on the favorability of the anatomy.

Summary
Cyanotic heart disease commonly presents in the neonatal period. Rapid diagnosis and referral are mandatory because patients can become unstable very quickly. Prostaglandin E1 promotes blood flow through the ductus arteriosus and is a useful stabilizing maneuver in many, but not all, of these conditions. Echocardiography and cardiac catheterization are the diagnostic tools of choice and early surgical intervention is often required, either for palliation or for definitive correction. Current surgical therapy for most lesions has evolved from early palliation and delayed repair to complete correction in early infancy with improved morbidity and mortality