Atrioventricular Septal Defect

Congenital malformation of the endocardial cushions: a deficient atrioventricular septum with a primum atrial septal defect, an inlet ventricular septal defect (complete form), and a common atrioventricular valve instead of separate mitral and tricuspid valves. It accounts for about 3 to 5% of congenital heart disease, about 0.3 to 0.4 per 1000 live births.

• Strongly associated with Down syndrome: about 40 to 50% of infants with Down syndrome have a congenital heart defect, and atrioventricular septal defect is the commonest lesion among them (about 40%). Also seen with heterotaxy syndromes and Ellis van Creveld syndrome.
• Forms: complete (common valve, primum atrial and inlet ventricular defects), partial (primum atrial defect with a cleft left atrioventricular valve and separate valve annuli, no ventricular defect), and intermediate or transitional (restrictive ventricular communication). Balanced forms have both ventricles of adequate size; unbalanced forms (right or left dominant) may need single ventricle palliation.
• Physiology of the complete form: a large left to right shunt at atrial and ventricular level with atrioventricular valve regurgitation. Pulmonary vascular resistance falls over the first weeks of life, so pulmonary flow rises sharply, and irreversible pulmonary vascular disease can develop by 6 to 12 months, and earlier in Down syndrome. Eisenmenger syndrome follows if the defect is left open.
• Untreated complete disease: heart failure in the first months, and most die in infancy or develop pulmonary vascular disease. Repair in infancy gives operative mortality of about 2 to 5%, with 10-year survival of about 90% or more.

• Complete form: breathlessness, sweating with feeds, poor weight gain and recurrent chest infections from 2 to 8 weeks of age, with tachypnoea, subcostal recession and hepatomegaly. Mild cyanosis on crying or with pulmonary hypertension. Hyperdynamic precordium, a loud pulmonary second sound, a soft systolic murmur at the lower left sternal edge, an apical systolic murmur from valve regurgitation and a mid-diastolic flow murmur.
• Partial form: often asymptomatic in childhood. Fixed splitting of the second heart sound, a pulmonary flow murmur and an apical pansystolic murmur of left atrioventricular valve regurgitation. In adults: exertional dyspnoea, palpitations (atrial flutter or fibrillation) and right heart failure.
• Features of Down syndrome (hypotonia, characteristic facies, single palmar crease) should be sought.
• Differential diagnosis: large ventricular septal defect, secundum atrial septal defect, persistent truncus arteriosus, total anomalous pulmonary venous return, patent ductus arteriosus, isolated mitral regurgitation, cardiomyopathy, bronchiolitis, and pneumonia.
• Complications: heart failure, failure to thrive, pulmonary vascular disease and Eisenmenger syndrome, recurrent respiratory infection, endocarditis, left atrioventricular valve regurgitation, left ventricular outflow tract obstruction, atrial arrhythmias, and complete heart block (after surgery).

• ECG: superior (northwest) QRS axis, usually between minus 30 and minus 150 degrees, a prolonged PR interval, right bundle branch block pattern, and biventricular or right ventricular hypertrophy. The superior axis separates it from other septal defects.
• Chest X-ray: cardiomegaly, increased pulmonary vascular markings, prominent main pulmonary artery.
• Echocardiography: absent crux of the heart, common atrioventricular valve with its bridging leaflets and attachments, size of the atrial and ventricular components, balance of the ventricles, valve regurgitation and its mechanism, "gooseneck" deformity of the left ventricular outflow tract, aortic arch, and associated lesions (patent ductus, tetralogy features).
• Cardiac catheterisation is reserved for late presentation (older than 6 to 12 months) or suspected pulmonary hypertension: operable if pulmonary vascular resistance index is less than about 6 Wood units m2 with a pulmonary to systemic resistance ratio less than about 0.3. Higher values or a net right to left shunt mean repair carries unacceptable risk and Eisenmenger physiology is likely.
• Genetic assessment (karyotype or microarray) for Down syndrome and other syndromes. Thyroid function in Down syndrome.

• Counsel the family that complete repair is the definitive treatment, usually between 3 and 6 months of age, and that medical therapy is a bridge.
• Medical therapy for heart failure in infancy:
  • Furosemide 1 to 2 mg/kg per dose orally 2 to 3 times daily (maximum 6 mg/kg/day). Monitor sodium, potassium and creatinine.
  • Spironolactone 1 to 3 mg/kg/day in 1 to 2 divided doses, which also conserves potassium.
  • Captopril 0.1 mg/kg per dose 8-hourly, increased over days to 0.5 mg/kg per dose (maximum 2 mg/kg/day). Monitor blood pressure, creatinine and potassium; avoid in renal impairment or severe valve obstruction.
  • Digoxin has limited evidence in infants with a large shunt and is used only for refractory failure or atrial arrhythmia.
  • Nutrition: 120 to 150 kcal/kg/day by fortified feeds or nasogastric tube; treat anaemia, chest infections and gastro oesophageal reflux; give palivizumab or the local equivalent for respiratory syncytial virus prophylaxis where available.
• Surgical repair:
  • Complete defect: complete repair at 3 to 6 months (earlier if growth fails or heart failure is refractory; for Down syndrome ideally by 6 months because of early pulmonary vascular disease). Two patch, modified single patch or direct closure of the ventricular component, patch closure of the atrial component, and cleft closure with valve reconstruction.
  • Pulmonary artery banding as a palliative first stage for small or fragile infants, or complex anatomy, followed by later repair.
  • Partial defect: elective repair at 1 to 5 years by patch closure of the primum defect and cleft closure; earlier if significant valve regurgitation or heart failure.
  • Unbalanced defects: single ventricle palliation with shunt or banding, bidirectional cavopulmonary shunt at 3 to 6 months, and Fontan completion at 2 to 4 years.
• Postoperative care:
  • Pulmonary hypertensive crises (common in the first 48 to 72 hours, especially in Down syndrome): deep sedation and muscle relaxation, 100% oxygen, mild hyperventilation to PaCO2 of 30 to 35 mmHg, inhaled nitric oxide 20 ppm, and sildenafil 0.5 to 1 mg/kg per dose 6 to 8-hourly after extubation (neonatal and infant evidence is limited).
  • Conduction: temporary pacing wires; complete heart block persisting beyond about 7 to 10 days needs a permanent pacemaker (about 1 to 3%).
  • Left atrioventricular valve regurgitation (the main cause of late problems): afterload reduction with captopril or ramipril 0.05 to 0.2 mg/kg/day, diuretics, and surgical valve repair or replacement for symptomatic or progressive regurgitation (reoperation in about 10 to 20%).
  • Left ventricular outflow tract obstruction (about 5 to 10%): resection when the peak gradient is 50 mmHg or more.
• Eisenmenger physiology: do not close. Specialist led pulmonary vasodilator therapy, for example bosentan 62.5 mg orally twice daily for 4 weeks then 125 mg twice daily (liver function monthly), or sildenafil 20 mg three times daily; avoid dehydration, pregnancy, and high altitude.
• Endocarditis prophylaxis, only after repair with prosthetic material, with residual defects beside prosthetic material, or previous endocarditis: amoxicillin 2 g orally (50 mg/kg in children) 30 to 60 minutes before dental procedures; azithromycin or clarithromycin 500 mg (15 mg/kg in children) if allergic to penicillin (clindamycin is no longer recommended).
• Special groups:
  • Down syndrome: screen for hypothyroidism, hearing and visual problems, and airway disorders; anaesthetic care for atlantoaxial instability; higher risk of pulmonary hypertensive crisis.
  • Pregnancy: repaired defects with good function and no pulmonary hypertension are usually tolerated; valve regurgitation, residual shunt and arrhythmia need assessment before conception; unrepaired disease with pulmonary hypertension carries maternal mortality of about 30 to 50%, so pregnancy is advised against.
  • Adults: surveillance for atrial arrhythmia (anticoagulation with warfarin to INR 2.0 to 3.0, or apixaban 5 mg twice daily, reduced to 2.5 mg twice daily if two of age 80 or more, weight 60 kg or less, creatinine 133 micromol/L or more), heart block, and valve disease.
• Red flags: poor feeding with tachypnoea, weight loss, new cyanosis, syncope or palpitations, new valve murmur, fever with a murmur, loss of the superior axis on ECG with heart block.
• Follow up: after repair, review at 6 weeks, 6 months and 12 months with ECG and echocardiography, then every 1 to 2 years in childhood and every 1 to 3 years in adulthood. Refer to a specialist congenital cardiology service for life.