Ventricular Septal Defect
- A ventricular septal defect (VSD) is an opening in the ventricular septum, resulting in a communication between the left ventricle (LV) and the right ventricle (RV). The ventricular septum can be divided into four major areas:
- Inlet/canal septum
- Membranous/conoventricular septum
- Muscular septum (largest)
- Conal/infundibular/outlet septum (includes conal septal hypoplasia and malalignment types)
- There are several corresponding types of VSDs that have different natural histories and associated problems:
- Inlet/canal VSDs: usually part of an atrioventricular (AV) canal defect, 5–7% of all VSDs
- Membranous/conoventricular VSDs: 80% of all VSDs by classic teaching; fewer than muscular VSDs by echocardiographic data
- Muscular VSDs: usually single and small but can be multiple and of variable size; 5–20% of all VSDs by classic teaching, but a large percentage are inaudible
- Conal septal hypoplasia/outlet VSDs: usually large and unrestrictive; associated with aortic valve (AoV) cusp prolapse and aortic insufficiency
- Anterior malalignment VSDs: usually associated with RV outflow tract obstruction; paradigms: tetralogy of Fallot, double outlet RV
- Posterior malalignment VSDs: usually associated with LV outflow tract obstruction; paradigms: subaortic stenosis with coarctation or interrupted aortic arch
- There may also be multiple VSDs of different types in a single patient. Many complex forms of congenital heart disease include a VSD.
- VSDs are the most common form of congenital heart disease, occurring in ~1.5 to 5.7 per 1,000 term births and ~4.5 to 7 per 1,000 preterm births, by classic teaching.
- Echocardiographic data show a higher incidence of ~50 per 1,000 live births, mostly asymptomatic muscular VSDs.
- Sibling and offspring recurrence risk for VSDs is estimated to be ~3–4%.
- VSD is the most common lesion in trisomy 21, 13, and 18, but >95% of children with VSDs have normal chromosomes.
- Congenital heart disease that includes a conal septal malalignment VSD (e.g., tetralogy of Fallot) or VSD with a conotruncal malformation (e.g., truncus arteriosus or interrupted aortic arch type B) has a 13–50% incidence of microdeletion of chromosome 22 (22q11.2 deletion syndrome). In a recent series, 7% of patients with an isolated membranous/conoventricular VSD had a 22q11.2 deletion.
- Both the size of the VSD and the ratio of pulmonary (PVR) to systemic vascular resistance (SVR) determine the direction and amount of shunting.
- Small VSD: The VSD imposes high resistance to flow with a large LV-to-RV pressure gradient, usually resulting in normal RV pressures. The restrictive size results in a small left-to-right shunt. The VSD size is usually ≤1/4 the size of the AoV annulus. The workload of the ventricles is normal.
- Moderate VSD: The VSD imposes modest resistance to flow, usually resulting in mildly elevated RV pressures. The amount of shunting can still be large and is determined by the PVR/SVR ratio. The VSD size is usually 1/3 to 2/3 the size of the AoV annulus. The workload of the ventricles is increased.
- Large VSD: The VSD imposes no resistance to flow and is unrestrictive, resulting in systemic RV pressures and RV hypertension. The workload of the ventricles is markedly increased.
- The lower the PVR/SVR ratio, the greater the degree of left-to-right shunting. A large left-to-right shunt leads to pulmonary vascular congestion, tachypnea, tachycardia, and hepatomegaly, all signs of congestive heart failure (CHF). The amount of CHF correlates directly with shunt size and usually peaks at 6 to 8 weeks of age, timed with the nadir of PVR and physiologic anemia. Lack of significant CHF in patients with a large VSD signifies elevated PVR and requires careful evaluation. Cardiac catheterization may be required in these patients to provide additional data.
- If a large VSD is left untreated, pulmonary vascular obstructive disease will eventually develop, leading to reversal of the shunt, cyanosis, and RV failure (Eisenmenger syndrome).
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