Which cardiac defect is the most common cause of mortality within the first week of life?

Hypoplastic left heart syndrome is characterized by underdevelopment of the left side of the heart, which includes structures such as the left ventricle, aorta, and mitral valve. This condition is particularly critical because it severely impairs the heart's ability to pump oxygenated blood to the body. Infants born with this defect often present with symptoms of heart failure and shock shortly after birth, leading to significant mortality within the first week if not treated promptly.

Immediate management is crucial and may involve surgical interventions or heart transplantation. The rapid decline in condition typically seen in these infants is what makes hypoplastic left heart syndrome the leading cause of mortality among congenital heart defects within the first week of life. In contrast, while other conditions like ventricular septal defect, atrial septal defect, and transposition of the great vessels can have serious implications, they would not typically lead to mortality as rapidly as hypoplastic left heart syndrome does in the newborn period.