Which condition has the highest likelihood of a left-to-right shunt in infancy?

Which condition has the highest likelihood of a left-to-right shunt in infancy?

• A. Truncus arteriosus
• B. Hypoplastic left heart syndrome
• C. Ventricular septal defect
• D. Transposition of the great arteries

Answer: (C)

A left-to-right shunt occurs whenever higher-pressure blood from the left side of the heart flows into the right side or pulmonary circulation through an abnormal connection. The ventricular septal defect provides a direct conduit between the left and right ventricles, so blood pumped by the left ventricle readily flows into the right ventricle and then to the lungs. Because the left ventricle operates at higher pressures, a sizable defect allows substantial left-to-right flow, leading to marked pulmonary overcirculation and early symptoms in infancy. This makes a ventricular septal defect the lesion most likely to produce a left-to-right shunt in this age group. Truncus arteriosus involves a single outflow tract giving both systemic and pulmonary branches, which can result in overcirculation as well, but the pattern is driven by mixing and the shared trunk rather than a straightforward LV-to-RV shunt. Hypoplastic left heart and transposition of the great arteries rely more on mixing through fetal/neonatal shunts (like the patent ductus arteriosus or a VSD) for systemic versus pulmonary blood flow, rather than a primary, direct left-to-right flow across a ventricular defect.

A left-to-right shunt occurs whenever higher-pressure blood from the left side of the heart flows into the right side or pulmonary circulation through an abnormal connection. The ventricular septal defect provides a direct conduit between the left and right ventricles, so blood pumped by the left ventricle readily flows into the right ventricle and then to the lungs. Because the left ventricle operates at higher pressures, a sizable defect allows substantial left-to-right flow, leading to marked pulmonary overcirculation and early symptoms in infancy. This makes a ventricular septal defect the lesion most likely to produce a left-to-right shunt in this age group.

Truncus arteriosus involves a single outflow tract giving both systemic and pulmonary branches, which can result in overcirculation as well, but the pattern is driven by mixing and the shared trunk rather than a straightforward LV-to-RV shunt. Hypoplastic left heart and transposition of the great arteries rely more on mixing through fetal/neonatal shunts (like the patent ductus arteriosus or a VSD) for systemic versus pulmonary blood flow, rather than a primary, direct left-to-right flow across a ventricular defect.