Hypoplastic right heart syndrome

Overview

Hypoplastic right heart syndrome (HRHS) is a rare and complex congenital heart defect in which the right-sided structures of the heart-such as the right atrium, right ventricle, pulmonary valve, and pulmonary artery are underdeveloped. This leads to insufficient blood flow from the heart to the lungs, resulting in low oxygen levels in the body. HRHS typically presents in the newborn period and requires immediate medical evaluation and intervention. It is considered the right-sided counterpart to hypoplastic left heart syndrome (HLHS).

Causes

Hypoplastic right heart syndrome occurs due to abnormal development of the heart during fetal life. While the exact cause is unknown, several factors may contribute:

• Genetic mutations or syndromes: Occasionally associated with chromosomal abnormalities

• Familial predisposition: A family history of congenital heart defects may increase the risk

• Environmental factors: Maternal diabetes, infections, or exposure to teratogens during pregnancy may play a role

The condition often arises spontaneously without a known cause in many cases.

Symptoms

Signs and symptoms of HRHS typically appear shortly after birth due to inadequate blood flow to the lungs and systemic hypoxia. Common symptoms include:

• Severe cyanosis (bluish skin, lips, or nails)

• Difficulty breathing (tachypnea or respiratory distress)

• Poor feeding and lethargy

• Cold extremities or weak pulses

• Heart murmur

• Failure to thrive

Symptoms may rapidly worsen as the ductus arteriosus (a fetal blood vessel that helps circulate blood) begins to close after birth.

Diagnosis

Diagnosis of HRHS is typically made during the newborn period, often through prenatal or postnatal evaluation. Key diagnostic steps include:

• Prenatal ultrasound and fetal echocardiogram: Can detect heart abnormalities during pregnancy

• Postnatal echocardiogram: Confirms the underdevelopment of right-sided heart structures and evaluates blood flow

• Pulse oximetry: Measures oxygen saturation and identifies hypoxia in newborn screening

• Chest X-ray and ECG: May be used to assess heart size and rhythm

• Cardiac catheterization: In complex cases, helps evaluate pulmonary artery pressures and anatomy

Early diagnosis is critical for initiating life-saving interventions and planning surgical treatment.

Treatment

Treatment of HRHS is aimed at improving blood flow to the lungs and ensuring oxygenation of the body. The approach depends on the severity of the condition and associated anomalies. Key treatment strategies include:

• Prostaglandin E1 infusion: To keep the ductus arteriosus open and maintain pulmonary circulation

• Oxygen therapy and stabilization: Including ventilatory support if needed

Surgical Options (Staged Palliation):

1. Shunt procedure (e.g., Blalock-Taussig shunt): Performed in the first days of life to direct blood from the aorta to the pulmonary arteries

2. Glenn procedure: Usually performed around 4–6 months of age to connect the superior vena cava to the pulmonary artery

3. Fontan procedure: Completed around 18 months to 3 years of age, rerouting venous return from the lower body directly to the lungs

Heart Transplantation:

• In severe or complex cases not amenable to surgery, heart transplantation may be considered

Prognosis

The prognosis for infants with hypoplastic right heart syndrome depends on the severity of the defect, the presence of associated anomalies, and the success of surgical interventions. With modern surgical techniques and specialized care, many children can survive into adolescence and adulthood. However, long-term complications can include:

• Arrhythmias or heart failure

• Protein-losing enteropathy

• Exercise intolerance

• Need for heart transplantation later in life

Lifelong cardiology follow-up and individualized care are essential to monitor cardiac function and manage complications over time.