Double Inlet Left Ventricle

Double inlet left ventricle is a univentricular atrioventricular connection in which both atria connect to a dominant left ventricle, with a small rudimentary right ventricular outflow chamber that gives rise to one or both great arteries. Management depends on pulmonary blood flow and on systemic outflow.

It accounts for about 1 to 2% of congenital heart disease. The aorta usually arises from the outflow chamber, with the great arteries transposed (commonly left transposed, with the aorta anterior and to the left) in most cases.

Pulmonary stenosis is present in about half of patients. Subaortic obstruction occurs through the bulboventricular foramen in those where the aorta arises from the outflow chamber, and aortic arch obstruction (coarctation) may coexist.

Atrioventricular conduction is abnormal, with the node displaced, so heart block occurs spontaneously and after surgery.

Pathophysiology.

Systemic and pulmonary venous blood mix in the single dominant ventricle, so saturation depends on the balance of pulmonary and systemic flow.

Unobstructed pulmonary flow causes heart failure in infancy and risk of irreversible pulmonary vascular disease. Pulmonary stenosis limits flow and causes cyanosis. A restrictive bulboventricular foramen causes subaortic obstruction, ventricular hypertrophy and systemic hypoperfusion.

Chronic volume load and cyanosis lead to ventricular failure, arrhythmia and, in the long term, failure of the Fontan circulation.

Presentation depends on the physiology. Infants with pulmonary overcirculation have tachypnoea, feeding difficulty, failure to thrive, sweating and hepatomegaly. Those with pulmonary stenosis are cyanosed. Those with subaortic or arch obstruction present with poor pulses and shock at duct closure. Examination: single second heart sound, murmurs of pulmonary stenosis or atrioventricular valve regurgitation, bradycardia in heart block.

• Echocardiography: both atria opening into the dominant ventricle (two inlets or a common inlet), outflow chamber position, ventriculo arterial connections, size of the bulboventricular foramen (peak gradient over 20 mmHg or a foramen area index under 2 cm2/m2 indicates obstruction), pulmonary stenosis, arch obstruction, atrioventricular valve function, and ventricular function.
• ECG: heart block, atrial or ventricular arrhythmia, abnormal Q waves, and atrial arrhythmia late. Ambulatory ECG.
• Saturation, haemoglobin, arterial blood gas and lactate. MRI or CT for anatomy and ventricular volumes.
• Cardiac catheterisation before Glenn and Fontan stages: pulmonary artery pressure, pulmonary vascular resistance (indexed under 3 Wood units x m2 for Fontan candidacy), ventricular end diastolic pressure and branch pulmonary artery size.

Differential diagnosis.

• Tricuspid atresia, hypoplastic left heart syndrome, and unbalanced atrioventricular septal defect.
• Transposition of the great arteries with large ventricular septal defect.
• Corrected transposition and complex single ventricle forms with heterotaxy.
• Critical coarctation or interrupted aortic arch.

Neonatal stabilisation (duct dependent lesions).

• Alprostadil intravenously: 0.05 to 0.1 microgram/kg/min to reopen the duct, then 0.01 to 0.03 microgram/kg/min. Watch for apnoea (intubate for transport), fever and hypotension. Use for pulmonary stenosis with ductal pulmonary flow and for arch obstruction with ductal systemic flow.
• Target saturation 75 to 85% in the balanced circulation. Avoid excess oxygen and hyperventilation when pulmonary flow is high.
• Heart failure from pulmonary overcirculation: furosemide 1 mg/kg orally or intravenously every 12 hours (maximum 6 mg/kg daily), 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, with potassium and creatinine at 1 to 2 weeks. Digoxin 5 to 10 microgram/kg daily in 2 doses with level monitoring may be used.
• Heart block: temporary pacing, then a permanent pacemaker for symptomatic or high grade block.

Surgical strategy (staged to the Fontan circulation).

• Excessive pulmonary flow: pulmonary artery banding in infancy (about 3 months), when no subaortic obstruction.
• Pulmonary stenosis with low flow: Blalock-Taussig-Thomas shunt.
• Subaortic obstruction, arch obstruction or restrictive bulboventricular foramen: Damus-Kaye-Stansel anastomosis (pulmonary trunk to aorta) with arch repair, and a shunt or band, or a Norwood type operation. Resecting the bulboventricular foramen risks heart block and is avoided.
• Bidirectional Glenn procedure at 3 to 6 months, then Fontan completion at 2 to 4 years, when pulmonary vascular resistance and ventricular function allow.
• Balanced circulation (moderate pulmonary stenosis without obstruction): observe and defer surgery, with close surveillance. Biventricular conversion is rarely suitable.
• Transplantation for failing univentricular circulation.

Medical therapy.

• Aspirin 3 to 5 mg/kg orally once daily after shunt placement or Fontan completion. Warfarin to INR 2.0 to 3.0 is used after Fontan for thrombus risk, atrial arrhythmia or low flow.
• Ventricular dysfunction: carvedilol 0.05 mg/kg twice daily, doubled every 2 weeks to a maximum of 0.4 to 0.5 mg/kg twice daily when stable. Add spironolactone 1 to 3 mg/kg daily in 1 to 2 doses with potassium checks at 1 and 4 weeks.
• Atrial tachyarrhythmia in older patients: avoid class I drugs. Use beta blockers (metoprolol succinate 25 to 100 mg once daily) and amiodarone 200 mg daily after loading in adults, with thyroid and liver tests every 6 months; early catheter ablation. Anticoagulate by INR 2.0 to 3.0.
• Cyanosis in older patients: manage hydration and iron deficiency (ferrous sulphate 200 mg orally once daily, with haemoglobin and ferritin at 4 weeks). Avoid routine phlebotomy.
• RSV prevention in infants under 2 years: palivizumab 15 mg/kg intramuscularly monthly during the season, or nirsevimab single dose (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.

Fontan complications. Protein losing enteropathy (albumin, stool alpha-1 antitrypsin; treat with oral budesonide 9 mg daily or heparin, and look for obstruction), plastic bronchitis, liver fibrosis, thrombosis, arrhythmia and heart failure. Refer for catheter assessment, medical therapy and transplantation assessment.

Monitoring. Saturation, weight and growth at each visit. Echocardiography every 3 to 6 months in infancy, then yearly. ECG and ambulatory ECG yearly (more often with block). Annual liver ultrasound, albumin, creatinine and full blood count from adolescence in Fontan circulation. Catheterisation before each surgical stage.

Referral and escalation. Refer every infant with suspected single ventricle physiology to a paediatric cardiac centre at once. Urgent review for cyanosis, poor feeding, heart block, arrhythmia, syncope or heart failure.

Special groups.

• Pregnancy: counselling before conception; maternal and foetal risks are higher with Fontan circulation or cyanosis; avoid ACE inhibitors and warfarin from 6 to 12 weeks (low molecular weight heparin instead).
• Adults: lifelong follow up in an adult congenital heart disease centre.
• Region specific: in settings without staged surgery, balanced circulations may survive into adulthood, and management centres on cyanosis care, iron, hydration and endocarditis prevention.