What structural defect characterizes Tetralogy of Fallot (TOF)?

Tetralogy of Fallot (TOF) is characterized by a specific set of four congenital heart defects, one of which is a ventricular septal defect (VSD). The presence of a VSD is crucial in TOF as it allows for the mixing of oxygenated and deoxygenated blood between the left and right ventricles. This defect contributes significantly to the symptoms observed in affected individuals, such as cyanosis.

In addition to the VSD, TOF typically includes right ventricular outflow tract obstruction (often due to pulmonary stenosis), an aorta that is positioned directly over the ventricular septal defect (overriding aorta), and right ventricular hypertrophy. The combination of these structural anomalies is what defines TOF, and the VSD serves as the primary defect that underpins the pathophysiology of the condition.

The other listed conditions, such as coarctation of the aorta, transposition of the great vessels, and patent ductus arteriosus, are separate congenital heart anomalies that do not form part of the defining features of TOF. Recognizing these distinctions is vital for understanding the unique characteristics and management of different congenital heart defects.