Which of the following is NOT a component of Tetralogy of Fallot?

• A. Overriding Aorta
• B. Pulmonary Stenosis
• C. Ventricular Septal Defect
• D. Atrial Septal Defect

Answer: (D)

Understanding Tetralogy of Fallot means recognizing the four classic anatomic features that define the condition: a ventricular septal defect, pulmonary stenosis, an overriding aorta, and right ventricular hypertrophy. The combination of the VSD with obstruction to the right ventricular outflow (pulmonary stenosis) shifts deoxygenated blood across the VSD into the aorta, producing the cyanosis seen in TOF, and the right ventricular hypertrophy develops as the heart works harder to pump blood through the narrowed outflow tract. An atrial septal defect, on the other hand, is an opening at the atrial level and is not one of the defining components of Tetralogy of Fallot. It can occur with other congenital heart conditions, but it does not comprise the four-feature constellation that characterizes TOF.