October 6 2010 (Wednesday) - Tetrology of Fallot

A diagnosis I’d not heard of before….

Tetralogy of Fallot is a congenital heart defect which is classically understood to involve four anatomical abnormalities (although only three of them are always present). It is the most common cyanotic heart defect, representing 55-70%, and the most common cause of blue baby syndrome.

It was described in 1672 by Niels Stensen, in 1673 by Edward Sandifort, and in 1888 by the French physician Étienne-Louis Arthur Fallot, for whom it is named

Tetralogy of Fallot involves four heart malformations which present together:

A ventricular septal defect (VSD): a hole between the two bottom chambers (ventricles) of the heart. The defect is centered around the most superior aspect of the ventricular septum (the outlet septum), and in the majority of cases is single and large. In some cases thickening of the septum (septal hypertrophy) can narrow the margins of the defect.

Pulmonary stenosis: a narrowing of the right ventricular outflow tract and can occur at the pulmonary valve (valvular stenosis) or just below the pulmonary valve (infundibular stenosis). Infundibular pulmonic stenosis is mostly caused by overgrowth of the heart muscle wall (hypertrophy of the septoparietal trabeculae),  however the events leading to the formation of the overriding aorta are also believed to be a cause. The pulmonic stenosis is the major cause of the malformations, with the other associated malformations acting as compensatory mechanisms to the pulmonic stenosis. The degree of stenosis varies between individuals with TOF, and is the primary determinant of symptoms and severity. This malformation is infrequently described as sub-pulmonary stenosis or subpulmonary obstruction

Overriding aorta: An aortic valve with biventricular connection, that is, it is situated above the ventricular septal defect and connected to both the right and the left ventricle. The degree to which the aorta is attached to the right ventricle is referred to as its degree of "override." The aortic root can be displaced toward the front (anteriorly) or directly above the septal defect, but it is always abnormally located to the right of the root of the pulmonary artery. The degree of override is quite variable, with 5-95% of the valve being connected to the right ventricle

Right ventricular hypertrophy: The right ventricle is more muscular than normal, causing a characteristic boot-shaped (coeur-en-sabot) appearance as seen by chest X-ray. Due to the misarrangement of the external ventricular septum, the right ventricular wall increases in size to deal with the increased obstruction to the right outflow tract. This feature is now generally agreed to be a secondary anomaly, as the level of hypertrophy generally increases with age

(shamelessly blagged from Wikipedia)