A defect of atrioventricular valves (i.e., mitral and tricuspid valves) as well as the atrial and/or ventricular septum; previously referred to as endocardial cushion defects.

Etiology

• Strongly associated with Down syndrome
• Association with maternal diabetes and obesity has been shown in some studies.

Pathophysiology

• Complete form (ASD and VSD + single AV valves) → atrial and ventricular left-to-right shunt → excessive pulmonary blood flow and biventricular volume overload → pulmonary hypertension and heart failure
• Partial form (ASD only) → atrial left-to-right shunt → symptoms that may remain minimal until adulthood
• In both forms: abnormal AV valve → AV valve regurgitation → in utero heart failure (nonimmune hydrops fetalis)