Ventricular Septal Defect

Hole in the interventricular septum producing a left to right shunt. The most common congenital heart lesion at birth: about 2 to 5 per 1000 live births and about 20 to 30% of congenital heart disease.

• Types: perimembranous (about 70%), muscular (about 5 to 20%), inlet (about 5 to 8%), and doubly committed subarterial (about 5% in Western populations, up to 25 to 30% in East Asian populations; high risk of aortic cusp prolapse and regurgitation).
• Mechanism: pulmonary vascular resistance falls over the first 6 to 8 weeks of life, so a large defect shunts progressively more blood to the lungs, causing left atrial and ventricular volume overload and heart failure. If left open, a large defect causes irreversible pulmonary vascular disease and Eisenmenger syndrome (shunt reversal with cyanosis).
• Spontaneous closure: up to 80 to 90% of small muscular defects and about 30 to 50% of perimembranous defects close, mostly by 2 to 5 years of age. Subarterial and inlet defects rarely close.

• Small restrictive defect: asymptomatic, loud pansystolic murmur at the left lower sternal edge, often with a thrill, normal second heart sound.
• Moderate to large defect: breathlessness and sweating with feeds, poor weight gain, recurrent chest infections, tachypnoea, hepatomegaly, onset at 2 to 8 weeks. Murmur may be soft; mid-diastolic apical flow murmur, loud pulmonary component of the second heart sound.
• Eisenmenger syndrome: cyanosis, clubbing, polycythaemia, right ventricular heave, loud single second heart sound, loss of the pansystolic murmur.
• Complications: heart failure, endocarditis, aortic regurgitation from cusp prolapse, double chambered right ventricle, arrhythmia, pulmonary hypertension.
• Differential diagnosis: pulmonary stenosis, mitral regurgitation, tricuspid regurgitation, patent ductus arteriosus, atrioventricular septal defect, hypertrophic cardiomyopathy, innocent murmur.

• ECG: normal when small; left ventricular hypertrophy (moderate), biventricular hypertrophy (large), right ventricular hypertrophy with pulmonary hypertension.
• Chest X-ray: cardiomegaly and increased pulmonary vascular markings when the shunt is large.
• Echocardiography: site and size, direction of flow, pressure gradient across the defect (a peak gradient of 64 mmHg or more with normal arm BP suggests a restrictive defect), left atrial and ventricular size, estimated pulmonary artery pressure, aortic cusp prolapse, associated lesions.
• Cardiac catheterisation when pulmonary hypertension is suspected: Qp:Qs (pulmonary to systemic flow ratio) greater than 1.5 with pulmonary vascular resistance index less than 4 Wood units m2 supports closure; 4 to 8 Wood units m2 is borderline and needs vasoreactivity testing; greater than 8 Wood units m2 with a net right to left shunt means closure is contraindicated.

• Small restrictive defect with no symptoms: observation, review every 1 to 2 years in childhood then every 3 to 5 years; no restriction of activity.
• Infants in heart failure:
  • Furosemide 1 to 2 mg/kg per dose orally 2 to 3 times daily (maximum 6 mg/kg/day), with spironolactone 1 to 3 mg/kg/day in 1 to 2 divided doses and potassium monitoring.
  • Captopril 0.1 mg/kg per dose 8-hourly, increased gradually to 0.5 mg/kg per dose (maximum 2 mg/kg/day); monitor creatinine, potassium and blood pressure.
  • Digoxin has limited evidence in this setting and is not routinely needed.
  • Nutrition: 120 to 150 kcal/kg/day with fortified milk or nasogastric feeding; treat anaemia and chest infections promptly.
• Surgical closure indications:
  • Heart failure or poor growth despite medical therapy, usually by 3 to 6 months.
  • Large defect with pulmonary hypertension at any age within the first year, ideally before 6 to 12 months.
  • Aortic cusp prolapse with progressive regurgitation, history of endocarditis, or double chambered right ventricle.
  • Older children and adults: Qp:Qs of 1.5 or more with left ventricular volume overload, with pulmonary vascular resistance index less than 4 Wood units m2.
  • Technique: patch closure under cardiopulmonary bypass; operative mortality less than 1 to 2%; complete heart block in about 1%; residual shunt and tricuspid regurgitation are the other main complications.
• Device closure for selected muscular and perimembranous defects with adequate rims; risk of complete heart block in perimembranous defects is about 1 to 5% and may occur late. Perventricular hybrid closure for small infants with muscular defects.
• Pulmonary artery banding as a palliative step for infants with multiple muscular defects or unfit for bypass.
• Eisenmenger syndrome: do not close. Use specialist led pulmonary vasodilators, for example sildenafil 20 mg three times daily or bosentan 62.5 mg twice daily for 4 weeks then 125 mg twice daily (check liver enzymes monthly). Venesection only for symptomatic hyperviscosity with haematocrit greater than 65%, with volume replacement; avoid dehydration, iron deficiency and air in IV lines; avoid pregnancy.
• Endocarditis prophylaxis: needed only for prior endocarditis, within 6 months of repair using prosthetic material, or for residual defects next to prosthetic material. 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). Maintain meticulous oral hygiene in all patients.
• Special groups: pregnancy (small or repaired defects are tolerated; Eisenmenger syndrome carries maternal mortality of about 30 to 50% and pregnancy should be avoided and terminated early if it occurs); renal impairment (adjust captopril and spironolactone); elderly (closure rarely indicated unless there is volume overload).
• Red flags: failure to thrive, tachypnoea at rest, new cyanosis, new diastolic murmur, fever with a murmur.
• Follow up: after surgical repair at 6 weeks, 6 months and 1 year, then every 2 to 5 years with ECG (heart block) and echocardiography (residual shunt, aortic regurgitation).