ABSTRACT
Structural abnormalities of the fetal heart typically include, but are not restricted to, atrioventricular septal defects (AV canal), hypoplastic left ventricle, hypoplastic right ventricle, large ventricular septal defects, atrial septal defects, Ebstein anomaly, and premature closure of the ductus arteriosus. The pathophysiology underlying the NIH associated with these conditions is diverse and complex, but is mainly attributable to an increase in the systemic venous pressure resulting from obstruction of right heart output as well as the transmission of systemic arterial pressure to the right heart by means of several pathologic shunts, including the primary or secondary closure of the foramen ovale. Other mechanisms involve obstruction to flow (cardiac tumors such as rhabdomyomas, which are associated in half of the cases to tuberous sclerosis) and the development of significant arteriovenous shunts with an increase in cardiac output, cardiac hypertrophy, and eventually heart failure (sacrococcygeal teratomas and placental chorioangiomas). Aneurysm of the great vein of Galen is a large cerebral arteriovenous malformation that conveys to right-to-left shunting through causing congestive heart failure and hydrops. With the exception of few case reports claiming successful outcomes, the presence of heart failure in these cases imposes a poor prognosis for the fetus.
