A 15-day-old infant with respiratory distress is brought into the emergency department. A quick observation suggests that the infant has slight cyanosis, hepatosplenomegaly, and features consistent with Down syndrome. The cardiac examination demonstrates a loud first heart sound, a wide and fixed split second heart sound, a low-pitched, mid-diastolic murmur at the lower left sternal border, and a harsh apical holosystolic murmur in the mitral area. Which of the following cardiac conditions is most likely to explain the heart defect in this infant with probable Down syndrome?
- Complete atrioventricular (A-V) canal (endocardial cushion defect)
- Transposition of the great vessels
- Total anomalous venous return
- Hypoplastic left heart
- Tricuspid atresia