Tetralogy of fallot anatomy


 * Associate Editors-In-Chief: Priyamvada Singh, M.B.B.S. [mailto:psingh@perfuse.org]; Assistant Editor-In-Chief: Kristin Feeney, B.S. [mailto:kfeeney@perfuse.org]

Overview
Tetralogy of Fallot has four characteristic components i.e. pulmonic stenosis, right ventricular hypertrophy, ventricular septal defect and over-riding of the aorta

Anatomic morphology
The defect is due to anterocephalad deviation of the outlet septum. This defect in outlet septum in turn leads to the four characteristic features Primary four malformations
 * Ventricular septal defect: a hole between the two bottom chambers (ventricles) of the heart. The defect is centered around the 'outlet septum', the most superior aspect of the septum, and in the majority of cases is single and large. In some cases septal hypertrophy can narrow the margins of the defect.
 * Pulmonic stenosis: Right ventricular outflow tract obstruction
 * A narrowing at (valvular stenosis, seen in approximately 20-25% case) or just below (infundibular stenosis, seen in around 50% of cases) the pulmonary valve.
 * The stenosis is mostly the result of hypertrophy of the septoparietal trabeculae, however the deviated outlet septum is believed to play a role.
 * The 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.
 * Tetralogy of fallot with pulmonary atresia or pseudotruncus arteriosus is a severe variant in which there is complete obstruction of the right ventricular outflow tract and absence of the pulmonary trunk. In these individuals, there is complete right to left shunting of blood.  The lungs are perfused via extensive collaterals from the systemic arteries.
 * Overriding aorta: defined as when the aortic valve is not restricted to the left ventricle, thus having biventricular connections. The aortic root can be moved anteriorly or override the septal defect, but it is still 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 coeur-en-sabot (boot-shaped) appearance as seen by chest X-ray. Due to the misarrangement of the external ventricular septum, the right ventricular wall increase 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.


 * There is anatomic variation between the hearts of individuals with tetralogy of Fallot. The degree of right ventricular outflow tract obstruction varies between patients and is generally determines clinical symptoms and disease progression.  Tetralogy of Fallot may present with other anatomical anomalies, including:
 * 1) Stenosis of the left pulmonary artery, in 40% of patients
 * 2) A bicuspid pulmonary valve, in 40% of patients
 * 3) Right-sided aortic arch, in 25% of patients
 * 4) Coronary artery anomalies, in 10% of patients
 * 5) An atrial septal defect, in which case the syndrome is sometimes called a pentalogy of Fallot
 * 6) An atrioventricular septal defect
 * 7) Partially or totally anomalous pulmonary venous return
 * 8) Forked ribs and scoliosis

