Tetralogy of Fallot

Anatomy Tetralogy of Fallot represents 10% of all congenital heart defects and is the most common form of cyanotic heart disease. A Danish scholar, Nicholas Steno, first described the defect in 1673, 200 years before Fallot. One hundred years later, numerous other reports were published from postmortem cardiac examinations. The French physician, Arthur Fallot, was the first to make an accurate bedside diagnosis with later validation at post mortem. He later published a review of the French literature on the maladie bleue in 1888, his name then becoming popularly associated with the malformation Tetralogy of Fallot comprises four anatomical abnormalities: (i) a large unrestrictive VSD; (ii) RVOT obstruction; (ill) overriding of the aorta above the RVOT; and (iv) RV hypertrophy (Fig. 20.4). In reality, there is a spectrum of abnormalities ranging from TOF with P A, where there is total obstruction to RV outflow, through TOF with PS (the "classic" tetralogy), to TOF with absent PV. Embryologically, TOF is believed to result from incomplete rotation and faulty partition of the conotruncus uring septation. d The VSD is perimembranous, large (usually the same size as the aortic valve), and unrestrictive. It is also important to note that the cardiac conduction tissue lies in close proximity to the margins of the VSD and may be damaged during repair producing temporary or permanent heart block. Because of clockwise rotation, the aorta overrides the VSD and thus has a biventricular origin. Additionally, the aortic arch lies to the right in 25% of TOF patients and may be associated with mirror image branching of the head vessels. There may be an aberrant origin of the ipsilateral subclavian artery from the descending aorta in some patients, and rarely, there may be an isolated origin of the left subclavian artery from the pulmonary artery. These abnormalities have important implications when electing the surgical approach for the placement of palliative shunts. s