In medicine, the tetralogy of Fallot (described by Etienne Fallot, 1850 - 1911, Marseille) is a significant and complex congenital heart defect, involving four different heart malformations:

1. A ventricular septal defect (VSD), a hole between the two bottom chambers (ventricles) of the heart.
2. Right ventricular outflow tract obstruction, a narrowing at or just below the pulmonary valve.
3. The aorta is positioned over the ventricular septal defect instead of in the left ventricle.
4. The right ventricle is more muscular than normal.

Pseudotruncus arteriosus is a particularly severe variant of the tetralogy of Fallot, in which there is complete obstruction of the right ventricular outflow tract. In these individuals, there is complete right to left shunting of blood. The lungs are perfused via collaterals from the systemic arteries. These individuals are severely cyanotic and will have a continuous murmur on physical exam due to the collateral circulation to the lungs.

Pathophysiology

The tetralogy of Fallot generally results in low oxygenation of blood due to mixing of desaturated and saturated blood in the ventricles and preferential flow of blood from the ventricles to the aorta because of obstruction to flow through the pulmonary valve. It is often evidenced by a bluish tint to the baby's skin (cyanosis). However there are "pink Fallots" in which the degree of obstruction in the pulmonary tract (right ventricular outflow, pulmonary valve and pulmonary arteries) is low. Blood flows preferentially from the ventricles to the lungs and only minimal desaturation occurs in the systemic circulation because of mixing of saturated and desaturated blood in the ventricles. This degree of desaturation may be undetectable to the eye and requires a pulse oximeter to identify it.

Even children who are generally not too deeply cyanosed (blue) may develop acute severe cyanosis or "spells". The precise mechanism of spelling is in doubt but certainly this is a dangerous event and presumably results from an increase in resistance to blood flow to the lungs with increased preferential flow of desaturated blood to the body. Such spells may be treated with beta-blockers such as propranolol, but acute episodes may require rapid intervention with oxygen, morphine and phenylephrine (to increase blood pressure).

Treatment

The condition was initially thought untreatable until Dr. Alfred Blalock (Baltimore, 1899 - 1964), assisted by Vivien Thomas, (or, arguably, Vivien Thomas assisted by Dr. Blalock) developed a procedure to alleviate the condition. The surgery involved joining an artery leaving the heart to an artery leading to the lungs, in an attempt to give the blood a second chance at oxygenation. This first blue baby operation came to be known as the Blalock-Taussig shunt. The idea of this procedure came from Helen B. Taussig (there is some historical dispute over exactly where priority and credit should be given, as Blalock, Thomas, and Taussig have each given different accounts which are difficult to confirm). The term Blue baby syndrome is sometimes applied to the tetralogy of Fallot, but is less specific and includes other conditions.

Since then, other methods of treatment have become available, including increasing the size of the opening from the heart to the pulmonary artery using a balloon catheter, or actually removing/reconstructing the valve leading from the heart to the lungs.

Additionally, recent developments in pediatric heart surgery have allowed actual open-heart reconstruction of the interior defects present in hearts with this condition.

Adults who have undergone surgery for this disorder usually lead normal lives but antibiotic prophylaxis is often indicated when the adult undergoes dental treatment in order to prevent infective endocarditis.

External links

• Information by University of Michigan Health System
• Diagram of the condition