Hypoplastic Right Heart Syndrome

Hypoplastic right heart syndrome is a group of congenital lesions with an underdeveloped right ventricle and tricuspid valve, giving obstructed or absent flow to the lungs. The commonest forms are pulmonary atresia with intact ventricular septum, tricuspid atresia, and critical pulmonary stenosis with a hypoplastic right ventricle. Pulmonary blood flow depends on the arterial duct.

Pulmonary atresia with intact ventricular septum occurs in about 4 to 8 of every 100,000 live births. Tricuspid atresia accounts for under 3% of congenital heart disease. Both present in the first days of life with cyanosis.

In pulmonary atresia with intact septum, a minority have right ventricle dependent coronary circulation: coronary arteries fed by the right ventricle through sinusoids, with proximal stenosis or atresia. Decompressing the right ventricle in these patients causes myocardial infarction.

Outcome has improved. Survival to adulthood is expected in many patients, but the circulation is palliated, not repaired.

Pathophysiology.

Obstruction between the right ventricle and the pulmonary arteries, or absence of the tricuspid connection, means that blood reaches the lungs only through the arterial duct (or aortopulmonary collaterals). When the duct closes, cyanosis becomes severe.

In pulmonary atresia with intact septum, a high pressure right ventricle may drive blood into coronary sinusoids. In tricuspid atresia, blood must cross an atrial septal defect to the left heart, and the left ventricle supplies both circulations, with variable pulmonary flow through a ventricular septal defect.

Cyanosis in the first hours to days of life, worsening as the duct closes, with tachypnoea and a single second heart sound. In tricuspid atresia with a large ventricular septal defect and pulmonary overcirculation, heart failure may dominate. Murmurs vary (duct murmur, tricuspid regurgitation murmur in pulmonary atresia with intact septum). Hypoxic spells and acidosis occur with duct closure. Some cases are found antenatally.

• Foetal echocardiography at 18 to 22 weeks, then postnatal echocardiography: right ventricle size and morphology (tripartite or unipartite), tricuspid valve size (z-score), pulmonary valve atresia (membranous or muscular), duct patency, atrial septal defect size, and coronary sinusoids or fistulae.
• Pre-ductal and post-ductal saturation. Arterial blood gas and lactate. Hyperoxia test is rarely needed.
• Cardiac catheterisation or CT angiography: coronary anatomy and right ventricle dependent circulation, assessed before any right ventricular decompression.
• Features favouring a biventricular repair: tricuspid valve z-score greater than minus 2.5, three part right ventricle (inlet, trabecular and outlet), and no right ventricle dependent coronary circulation.
• Genetic testing and review for extracardiac anomalies.

Differential diagnosis.

• Pulmonary atresia with ventricular septal defect, tetralogy of Fallot with severe pulmonary stenosis.
• Ebstein anomaly with functional pulmonary atresia, and transposition of the great arteries.
• Total anomalous pulmonary venous return and persistent pulmonary hypertension of the newborn.
• Methaemoglobinaemia and lung disease.

Immediate stabilisation.

• Alprostadil intravenously: 0.05 to 0.1 microgram/kg/min to reopen or maintain the duct, then 0.01 to 0.03 microgram/kg/min. Watch for apnoea (intubate for transport), fever, hypotension and flushing. Prolonged use causes gastric outlet obstruction.
• Target saturation 75 to 85%. Give oxygen cautiously, since it promotes duct closure. Correct acidosis, anaemia and hypoglycaemia. Avoid excessive fluid.
• Restrictive atrial septum in tricuspid atresia: balloon atrial septostomy (Rashkind procedure) or stenting.
• Transfer to a paediatric cardiac centre at once.

Definitive strategy.

• Pulmonary atresia with intact septum with a suitable right ventricle (membranous atresia, tripartite right ventricle, tricuspid z-score over minus 2.5): transcatheter radiofrequency perforation and balloon valvotomy, with duct stenting or a shunt when saturation stays low, aiming for biventricular or one-and-a-half ventricle circulation.
• Right ventricle dependent coronary circulation: do not decompress the right ventricle. Proceed to single ventricle palliation or transplantation.
• Tricuspid atresia and other unsuitable right ventricles: single ventricle palliation, with a Blalock-Taussig-Thomas shunt in the neonate (or pulmonary artery banding when pulmonary flow is excessive), bidirectional Glenn procedure at 3 to 6 months, and Fontan completion at 2 to 4 years.

Medical therapy.

• Aspirin 3 to 5 mg/kg orally once daily after shunt or stent placement. Warfarin to INR 2.0 to 3.0 is used for Fontan thrombus risk by specialist decision.
• Furosemide 1 mg/kg orally every 12 hours for pulmonary overcirculation or heart failure, with electrolytes and creatinine monitored. Enalapril 0.05 to 0.1 mg/kg orally daily, increased gradually to a maximum of 0.5 mg/kg daily, for ventricular dysfunction, with potassium and creatinine checks at 1 to 2 weeks.
• Hypercyanotic spell: knee chest position, oxygen, morphine 0.05 to 0.1 mg/kg intravenously, fluid 10 mL/kg, and phenylephrine 5 to 20 microgram/kg intravenously if needed.
• RSV prevention in infants under 2 years: palivizumab 15 mg/kg intramuscularly monthly during the season (up to 5 doses), or nirsevimab single dose by weight (50 mg under 5 kg, 100 mg for 5 kg or more) where available.
• Endocarditis prophylaxis: amoxicillin 50 mg/kg (maximum 2 g) orally 30 to 60 minutes before dental procedures.
• Home surveillance between stages: daily weight and saturation (target 75 to 90%), with early return for desaturation or poor feeding.

Monitoring. Saturation and weight at each contact. Echocardiography every 3 to 6 months in infancy. Catheterisation before Glenn and Fontan stages. Ambulatory ECG for atrial arrhythmia. Lifelong follow up of liver and kidney function, protein losing enteropathy and exercise capacity in Fontan circulation.

Referral and escalation. Refer every suspected case immediately to a paediatric cardiac centre. Urgent review for fall in saturation, poor feeding, lethargy or tachypnoea.

Special groups.

• Pregnancy: counselling before conception for women with a Fontan circulation; maternal and foetal risks are raised; avoid ACE inhibitors.
• Siblings: offer foetal echocardiography in later pregnancies.
• Region specific: where prostaglandin infusions and neonatal cardiac services are unavailable, survival is low, so early transfer and palliative support for families are needed.