Hypoplastic right ventricle is considerably rarer than hypoplastic left heart syndrome.
It is a complex cardiac malformation with a wide spectrum of presentations, the most serious of which frequently results in a single-ventricle functionality.
Prenatal sonographic features include pulmonary atresia with an intact ventricular septum, varying degrees of tricuspid atresia and tricuspid regurgitation, and varying degrees of hypoplasia of the right ventricular walls.
Neonates will be ductal-dependent and therefore delivery should be carefully coordinated in a center that can provide immediate pediatric cardiology intervention, prostaglandin infusion to maintain a patent ductus arteriosus, and ability to provide prompt catheter-based interventions such as pulmonary valvotomy, ductus arteriosus stenting, and balloon atrial septostomy.
Optimal management is individualized between catheter-based approaches that allow blood flow from right to left sides of the heart, together with open surgical systemic-pulmonary shunting.
Long-term outcome depends on whether a biventricular or univentricular repair is achieved.
Hypoplastic right ventricle (HRV) is also known as pulmonary atresia with intact ventricular septum (PA:IVS). The normally formed right ventricle becomes hypoplastic, in association with pulmonary atresia, and occasionally tricuspid atresia. The competence of the tricuspid valve determines the size of the right ventricle, with type I HRV being associated with a competent valve and small ventricle and type II HRV being associated with an incompetent valve and normal or large right ventricle (Romero et al., 1988). Another classification system is based on the degree of severity of right ventricular hypoplasia (Alwi, 2006). Group A patients have only mild right ventricular hypoplasia, with a well-developed infundibulum, beyond which the pulmonary arterial outflow tract is atretic. Group C patients have severe right ventricular hypoplasia, with an atretic infundibulum. Group B patients have a moderately HRV, but may have a reasonably well-developed infundibulum. Patients in Group C tend to have poor prognosis with long-term outcome being dependent on a single-ventricle repair.
In the setting of right ventricular hypoplasia, blood flows from the right to the left atria through the foramen ovale, and the left ventricle supplies both systemic and pulmonary circulations, the latter by retrograde flow through the ductus arteriosus. Additional cardiac malformations that may coexist include atrial and ventricular septal defects and transposition of the great vessels. Additionally, coronary arterial anatomy is frequently abnormal, and there may be varying degrees of tricuspid regurgitation or Ebstein malformation (see Chapter 46) (Daubney et al., 2002).
HRV is extremely rare, accounting for less than 3% of all cases of congenital heart disease diagnosed during the first year of life (Fyler et al., 1980). The overall population incidence is likely to be 1 to 2 per 10,000 livebirths (Hoffman and Kaplan, 2002). In another series, the livebirth prevalence was estimated at 4.1 per 100,000 livebirths (Daubney et al., 1998).