Perimembranous Ventricular Septal Defect Workup

For children with small ventricular septal defects (VSDs), no specific laboratory blood tests are indicated. Occasionally, in the evaluation of children with symptomatic large VSD, brain natriuretic peptide (BNP) is measured as a marker of congestive heart failure (CHF) severity.

Children who are maintained on diuretics and angiotensin-converting enzyme (ACE) inhibitors must have their electrolyte levels periodically measured.

Electrocardiography

Electrocardiographic findings vary depending on the VSD size and the degree of intracardiac shunting. Patients with small VSDs have normal ECG findings; large VSDs show left ventricular hypertrophy (LVH) (ie, volume overload), right ventricular hypertrophy (RVH) (ie, pressure overload), and left atrial enlargement.

Chest radiography

Small ventricular septal defects (VSDs) show normal cardiac size and normal pulmonary vascularity.

Large VSDs demonstrate cardiac enlargement and increased pulmonary vascular markings proportional to the size of left-to-right shunt, left atrial and left ventricular enlargement, posterior displacement of the left ventricular apex, and prominence of the main pulmonary artery segment.

Two-dimensional echocardiography and Doppler ultrasonography

Echocardiography is the most reliable noninvasive modality to identify the presence, size, number, and location of the VSD. Perimembranous VSDs are readily identified from the subcostal short- and long-axis planes, the apical 4-chamber, parasternal long axis, and parasternal short-axis scan planes.

Small VSDs (defined as VSD dimension less than half the size of the aortic annulus diameter) are usually isolated defects with otherwise normal cardiac anatomy and function. Large VSDs (defined as defect size equal to the diameter of the aortic annulus) typically have left atrial and left ventricular dilation with normal left ventricular systolic function. Dilation of the main and branch pulmonary arteries also is common.

Doppler echocardiography can be used to predict the intracardiac pressure gradient from the left ventricle to the right ventricle using the continuous wave Doppler tracing (modified Bernoulli equation = 4 [velocity squared]). If the systolic systemic pressure is known, in the absence of aortic outflow obstruction, right ventricle and pulmonary artery (in the absence of right ventricular outflow obstruction) systolic pressures can be predicted by subtracting the gradient between the ventricles from the aortic systolic blood pressure.

Color Doppler is useful to determine VSD location and size as well as the degree of intracardiac shunting.

Echocardiography is also essential to rule out other commonly associated congenital heart lesions, including atrial septal defects, patent ductus arteriosus, pulmonary valve stenosis, and complex congenital heart disease with an associated VSD.

Three-dimensional echocardiography

Real-time 3-dimensional echocardiography (RT3DE) can be used to characterize the ventricular septum. RT3DE allows accurate determination of VSD size, shape, and location. The short acquisition time and acceptable reconstruction time make this technique clinically applicable.^[3]

Magnetic resonance imaging

Cardiac magnetic resonance imaging (MRI) is a useful adjunct in the evaluation of large muscular VSDs. Black blood imaging at end-diastole reliably shows the anatomy of the ventricular septum, ventricular chambers, and great vessels. Bright blood gradient-echo dynamic images are useful for evaluating the anatomy in all segments of the cardiac cycle. Tiny muscular VSDs are not well seen using cardiac MRI.

Flow-sensitive phase contrast imaging is the criterion standard for determining the direction and magnitude of shunting. It can alleviate the requirement for cardiac catheterization in some cases.

Cardiac catheterization

Routine diagnostic cardiac catheterization is no longer required for perimembranous ventricular septal defects (VSDs). However, older children and adults with a large VSD usually require cardiac catheterization prior to surgical closure to assess PVR.

Indications for cardiac catheterization in patients with VSD include inadequate noninvasive echocardiographic assessment of the size, number, or location of the VSDs, as well as complicated associated anatomy.

Another indication is the requirement for additional hemodynamic data prior to medical management or surgical repair (eg, determination of PVR and its reactivity, quantitation of left-to-right shunting, exclusion of associated congenital heart defects).

Angiography

When angiography is employed, membranous VSDs are best demonstrated in the long axial oblique orientation.