Tetralogy of Fallot

Classic tetralogy of Fallot (TOF) is a congenital heart defect (CHD) that is comprised of 4 anatomical alterations: a large, anteriorly malaligned ventricular septal defect (VSD), an overriding aorta which results in infundibular (ie, sub-pulmonary) right ventricular outflow tract obstruction (RVOTO), and consequent right ventricular hypertrophy secondary to chronic systemic pressures. The pulmonary valve annulus is often hypoplastic, with a pulmonary valve that is dysplastic and stenotic. The VSD is most frequently located in the perimembranous septum; however, the defect can extend to the muscular septum, and infrequently, there might be additional muscular VSDs. A right aortic arch is observed in 20% to 25% of TOF. The clinical presentation will also depend on the associated cardiovascular anomalies in roughly 40% of patients with TOF. These may include atrial septal defects, patent ductus arteriosus, supravalvar pulmonary stenosis, branch pulmonary artery stenoses, hypoplastic branch pulmonary arteries, pulmonary valve atresia which may develop during fetal life as the subpulmonary infundibular narrowing progresses, a disconnected left pulmonary artery that originates from the ascending aorta formerly known as , a left pulmonary artery arising from the ductus arteriosus, absent left pulmonary artery, absent pulmonary valve, anomalous coronary arteries, anomalous pulmonary venous return, aortic incompetence, aortopulmonary window, and atrioventricular septal defect (AVSD).  Patients with TOF and pulmonary atresia may have a remnant of a pulmonary artery trunk with different calibers of the central pulmonary arteries and variable pulmonary tree anatomy. In approximately 50% of these patients, the right and left pulmonary arteries are confluent, and blood flow is ductal-dependent. In the other 50%, pulmonary flow is from multiple collateral vessels, usually from the descending thoracic aorta, and is not ductal-dependent. Occasionally, collateral arteries might arise from the head and neck, abdominal aorta, or coronary arteries. Surgical repair requires unifocalization of the many aortopulmonary collaterals, which can be quite challenging. TOF associated with rudimentary pulmonary valve leaflets, which occurs in 3% to 6% of cases, is known as “TOF with absent pulmonary valve.” In these patients, the main and branch pulmonary arteries are aneurysmal. Some degree of RVOTO is due to the presence of a small pulmonary annulus. The ductus arteriosus is usually absent, and approximately 50% have a right-sided aortic arch. Occasionally, one of the branch pulmonary arteries may arise from the aorta or may be absent. Approximately 2% of patients with TOF have an associated atrioventricular septal defect (AVSD). Because the RVOTO limits pulmonary overcirculation, these patients usually do not display symptoms of congestive heart failure. Therefore, primary surgical repair can be performed within the first few months of life.