Tetralogy of Fallot (TOF), a conotruncal abnormality, is a constellation of four findings: an aorta that overrides the right ventricular outflow tract; right ventricular outflow obstruction; a large subaortic VSD; and hypertrophy of the right ventricle . The frequent coexistence of an ASD can make for a pentalogy. Occasionally, patients with unrepaired TOF only present in adulthood because of a remarkable balance between the pulmonic obstruction and the VSD, which limits cyanosis.
Early palliation with a systemic-to-arterial shunt (e.g., Blalock-Taussig), which connects the subclavian and pulmonary arteries , facilitates growth of the pulmonary arteries and is a precursor to definitive surgical repair in the young child. Definitive repair often involves complete removal of the pulmonic valve and therefore results in wide open pulmonic regurgitation. Although the repair is tolerated for several years, the right ventricle eventually succumbs to volume overload and progressively increases in size.