Which congenital disorder exhibits a hypoplastic left atrium, but a normal left ventricle, and a PFO or an ASD?

Which congenital disorder exhibits a hypoplastic left atrium, but a normal left ventricle, and a PFO or an ASD?

• A. Ventricular septal defect
• B. Total anomalous pulmonary venous connection
• C. Right ventricular hypertrophy
• D. Coarctation of the aorta

Answer: (B)

The key idea is that when the pulmonary veins drain abnormally into the right-sided circulation instead of the left atrium, the left atrium receives little blood. That lack of flow makes the left atrium underdeveloped, or hypoplastic. For survival, there must be a passage between the atria—the PFO or an ASD—that allows mixing of oxygenated systemic venous blood into the left heart so that some blood can reach the left ventricle and the rest of the body. This combination—hypoplastic left atrium with a normal left ventricle and a communication between the atria—is characteristic of total anomalous pulmonary venous connection. Other options don’t fit this pattern. A ventricular septal defect involves a hole between the ventricles rather than the atria and doesn’t explain a small left atrium. Right ventricular hypertrophy reflects right-sided pressure/volume overload, not a hypoplastic left atrium. Coarctation of the aorta causes left ventricular pressure overload and hypertrophy, not a underdeveloped left atrium.

The key idea is that when the pulmonary veins drain abnormally into the right-sided circulation instead of the left atrium, the left atrium receives little blood. That lack of flow makes the left atrium underdeveloped, or hypoplastic. For survival, there must be a passage between the atria—the PFO or an ASD—that allows mixing of oxygenated systemic venous blood into the left heart so that some blood can reach the left ventricle and the rest of the body. This combination—hypoplastic left atrium with a normal left ventricle and a communication between the atria—is characteristic of total anomalous pulmonary venous connection.

Other options don’t fit this pattern. A ventricular septal defect involves a hole between the ventricles rather than the atria and doesn’t explain a small left atrium. Right ventricular hypertrophy reflects right-sided pressure/volume overload, not a hypoplastic left atrium. Coarctation of the aorta causes left ventricular pressure overload and hypertrophy, not a underdeveloped left atrium.