Congenital Heart Defect

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Ventricular septal defects (VSDs) are the most common form of congenital heart defect, accounting for 25% to 30% of all patients with congenital heart disease. The male:female ratio is 1. VSDs are the most common defect seen in the pediatric population. VSDs are usually a single defect, but they can occur in the setting of more complex congenital heart defects. Defects can be divided into restrictive defects (flow restricted between the LV and the RV with right ventricular pressure less than half of systemic levels) or nonrestrictive defects (with equal left and right ventricular pressures) . From 70% to 80% of VSDs can be characterized as restrictive, with the potential to close or become smaller . Nearly half of all VSDs are small, and up to 75% may close spontaneously. Even large defects can decrease in size. VSDs usually close by the age of 10 years. Spontaneous closure in adults is rare but has been reported.
The ventricular septum consists of the trabecular muscular septum, the inlet septum (formed from the endocardial cushion), the outlet or infundibular septum, and the membranous septum. Failure of growth, alignment, or fusion of these components results in a VSD. Perimembranous VSDs are the most common type, accounting for 75% to 80% of cases. A perimembranous defect occurs at the junction of the inlet, outlet, and trabecular septum and may extend variably into these regions. The perimembranous VSD underlies the septal leaflet of the tricuspid valve and may decrease in size or close spontaneously due to adherence of septal leaflet tissue to the defect, resulting in a ventricular septal aneurysm. Inlet septal defects account for 5% to 10% of VSDs. They occur in the muscular septum, under the mitral and tricuspid leaflets, due to deficiency of tissue from the endocardial cushion. Inlet VSDs rarely close spontaneously. Muscular defects or defects of the trabecular septum account for 20% of all VSDs. They may be located in various positions within the trabecular septum and may be multiple. Muscular VSDs tend to decrease in size with muscle growth and may close spontaneously. Outlet defects (also known as doubly committed subarterial defects or supracristal VSDs) account for 5% of all VSDs. They occur in the right ventricular outlet or conal portion of the septum, underlying both the pulmonary and aortic valves. Outlet defects do not close spontaneously, but their size can decrease due to prolapse of aortic cusp tissue through the defect (also resulting in aortic regurgitation).

The degree of left-to-right shunting depends on the size of the defect and the relative resistance of the systemic and pulmonary vascular beds. VSDs are characterized as small when the defect size is less than one-third of the aortic root size, and these are always restrictive. Pulmonary vascular resistance remains normal. With moderate restrictive defects, the defect is approximately half the size of the aortic valve, and there is moderate to severe left-to-right shunting. Patients with moderate defects may develop symptoms associated with LV volume overload and are at risk for developing pulmonary vascular disease. Large VSDs are nonrestrictive, with equal pressures in the left and right ventricles. There is a large left-to-right shunt initially, and the pulmonary circulation is exposed to systemic pressures early in the course of the disease. Patients with nonrestrictive VSDs usually develop irreversible pulmonary vascular disease within the first decade of life, eventually resulting in shunt reversal and Eisenmenger physiology.
The natural history of VSDs depends on the size and location of the defect. Small, restrictive defects with a Qp/Qs less than 1.5 to 1 do not place a hemodynamically significant load on the LV. Moderate or large defects cause pulmonary congestion and LV volume overload, which may lead to LV dysfunction and congestive heart failure. Pulmonary hypertension may occur with moderate defects. Larger defects are associated with a significant risk of pulmonary hypertension and pulmonary vascular obstructive disease. The Eisenmenger syndrome occurs in 10% of patients with VSDs. All patients are at risk for bacterial endocarditis and require antibiotic prophylaxis. Other complications include aortic cusp prolapse through the defect, resulting in aortic regurgitation and/or subaortic obstruction, and the development of a double-chambered RV due to hypertrophy of muscle bundles within the mid-right ventricular cavity.
The physical exam findings vary with the size of the defect. A patient with a small defect has a normal PMI, a normal S1 and S2, and a harsh pansystolic murmur associated with a systolic thrill. In addition to the murmur and thrill, patients with larger defects have evidence of LV enlargement with prominence and/or displacement of the apical impulse, a diastolic mitral inflow rumble, and frequently a gallop rhythm. With the development of pulmonary hypertension, the intensity of P2 increases, splitting of the second heart sound becomes narrowed, and the murmur decreases or disappears.
ECG findings are nonspecific. The ECG is normal with small defects. Larger defects are usually associated with the development of left ventricular hypertrophy (LVH) and ST-T wave changes. RVH may be seen with large defects or with the Eisenmenger syndrome. The CXR is normal with small defects, but cardiomegaly and pulmonary plethora are seen with larger defects. Patients with severe pulmonary vascular disease and shunt reversal (Eisenmenger physiology) have mild cardiomegaly or normal heart size with large central pulmonary arteries, peripheral pruning of the pulmonary vessels, and oligemic lung fields.
The diagnosis can be made by echocardiography with Doppler color flow mapping. With careful interrogation of the septum, the site and size of defects can be demonstrated The pressure gradient between the LV and the RV can be assessed by continuous-wave Doppler interrogation of the VSD jet, and right ventricular systolic pressure can be indirectly estimated from continuous-wave Doppler interrogation of the tricuspid regurgitation (TR) jet . Care must be taken with the latter approach because the TR jet may be contaminated by the VSD jet (particularly with perimembranous defects), resulting in inaccurate right ventricular pressure estimation. The interventricular pressure gradient may be inaccurate in the setting of tortuous or serpiginous defects where the modified Bernoulli equation is not applicable. Echocardiography may also reveal other associated defects, including aortic regurgitation.
Cardiac catheterization is generally reserved for patients in whom there is uncertainty regarding the size of the shunt and the pulmonary vascular resistance. The reversibility of pulmonary hypertension can be assessed with the administration of oxygen, nitric oxide, prostaglandins, or adenosine. Selective coronary angiography is usually performed for patients older than the age of 40 years if surgical repair is planned.
The clinical presentation depends on the size of the shunt. Patients with small defects are asymptomatic and have normal growth and development. The diagnosis in usually made on the basis of finding a loud holosystolic murmur. Larger shunts may result in symptoms of congestive heart failure in infancy as well as an increased susceptibility to pulmonary infections. The diagnosis of a VSD in adulthood is usually based on the incidental finding of a murmur or the development of a complication related to the VSD (e.g., endocarditis, aortic valve prolapse and regurgitation, or the Eisenmenger syndrome). Overall, the 25-year survival for all patients is 87% . Mortality increases with the size of the VSD.
Patients with symptomatic heart failure initially are treated with medical therapy, including diuretics and afterload reduction. Digoxin is often used in the pediatric setting. There are no randomized trials of medical therapy, but its use is indicated to stabilize the patient until surgical repair can be performed. Indications for surgery include severe intractable heart failure within the first 3 months of life, the presence of symptoms in older infants and children, and the presence of a moderate or large defect with a Qp/Qs greater than 2:1. Repair is also recommended for subarterial defects regardless of the shunt size due to the risk of aortic valve prolapse. Pulmonary vascular resistance should be below 8 Wood units (less than two-thirds systemic vascular resistance) for surgery to have long-term success. Repair is usually performed from the RA but occasionally through the RV, with placement of a patch or direct suture closure. Pulmonary artery banding is rarely performed. It is used to decrease pulmonary blood flow in patients with multiple defects or complex malformations that are not otherwise amenable to repair. Transcatheter device closure of VSDs appears to be feasible in some cases but is not widely available.
The prognosis is normal for patients with spontaneous closure of their VSD. Unoperated patients with an isolated small VSD and normal PVR have an excellent long-term prognosis, although they remain at risk for endocarditis . Unoperated patients with moderate to large shunts are at risk for multiple complications, including endocarditis, aortic regurgitation, LV dysfunction from chronic volume overload, arrhythmias, development of the Eisenmenger syndrome, and sudden death. Patients with subarterial VSDs (and occasionally perimembranous defects) may develop prolapse of the aortic cusp through the defect with the development of progressive aortic regurgitation. Overall, late outcome after early surgical closure of a VSD is excellent. Residual shunts are common, seen in up to 20% of cases after surgery, but are usually small. Late complications after surgical repair include endocarditis (if a residual shunt persists after surgery), surgically induced aortic or pulmonary regurgitation, and tricuspid regurgitation (if the septal leaflet was manipulated during the VSD repair). Arrhythmias and conduction disturbances may be seen. Right-bundle-branch block occurs in 30% to 60% of patients after surgical closure, first-degree AV block is seen in 10%, and complete heart block in 1% to 3% over long-term follow-up. Patients may have LV dysfunction with late repair of the defect or with significant aortic regurgitation. Patients may have persistent pulmonary hypertension after surgery or may develop progressive pulmonary hypertension despite successful closure of their shunt. There is an increased risk of sudden cardiac death after VSD closure, seen in 2% of patients. The etiology for sudden death has not been defined.
In general, patients undergoing early repair without a residual shunt, evidence of pulmonary hypertension, arrhythmias, or conduction block do not require long-term follow-up. Later repair of VSDs is associated with a risk of pulmonary hypertension and LV dysfunction, making long-term follow-up of these patients mandatory.

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