Approach Considerations
For children with small ventricular septal defects (VSDs), no specific laboratory blood tests are indicated. Occasionally, in the evaluation of children with a large, symptomatic VSD, brain natriuretic peptide (BNP) is measured as a marker of congestive heart failure (CHF) severity. Electrolytes should be periodically measured in children who are maintained on diuretics and angiotensin-converting enzyme (ACE) inhibitors.
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.
Histologic findings
No specific histologic abnormality is present. However, lung biopsy findings are sometimes used to stage degrees of pulmonary vascular obstructive disease.
Imaging Studies
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 the left-to-right shunt, left atrial and left ventricular enlargement, the posterior displacement of the left ventricular apex, and the prominence of the main pulmonary artery segment.
Two-dimensional echocardiography and Doppler
Two-dimensional (2D) echocardiography with Doppler color flow mapping is the most reliable noninvasive modality to identify the presence, size, number, and location of VSDs. Muscular VSD is readily identified from the apical, 4-chamber, parasternal long-axis and parasternal short-axis scan planes.
Small VSDs are usually isolated defects with otherwise normal cardiac anatomy and function. Large VSDs typically have left atrial and left ventricular dilation, with normal left ventricular systolic and diastolic function. Dilation of the main and branch pulmonary arteries is also common.
Echocardiography is also useful in determining the presence of associated intracardiac findings including right ventricular muscle bundles, infundibular stenosis, pulmonary valve stenosis, and associated left-sided lesions (eg, subaortic membrane, aortic stenosis, aortic cusp prolapse, coarctation of the aorta).
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] and subtracting the calculated gradient from the aortic systolic blood pressure [in the absence of aortic stenosis]). [12]
Color Doppler ultrasonography is useful in determining VSD location and size as well as the degree of intracardiac shunting.
These tests are 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 associated VSD.
Three-dimensional echocardiography
Real-time 3-dimensional echocardiography (RT3DE) can be applied to the characterization of 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.
RT3DE is especially helpful in the characterization of multiple muscular VSDs (Swiss cheese VSD). It allows for more precise interventional and surgical planning for this very challenging anatomy. [13]
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.
Diagnostic Cardiac Catheterization and Angiography
Catheterization
Routine diagnostic cardiac catheterization is no longer required for muscular ventricular septal defects (VSDs). However, it is indicated in some situations, such as inadequate noninvasive assessment of the size, number, or location of VSDs by echocardiography.
Other indications include a requirement to determine additional hemodynamic data prior to medical management or surgical repair (eg, determination of pulmonary vascular resistance (PVR) and its reactivity, quantitation of left-to-right shunting, exclusion of associated congenital heart defects).
Older children and adults with a large, unoperated VSD usually require cardiac catheterization prior to surgical closure to assess PVR.
Angiography
Muscular VSDs are best demonstrated in the long axial oblique orientation; anterior muscular defects are best demonstrated in right anterior oblique angulation, while posterior muscular defects are best visualized in the hepatoclavicular view. Angiography can be a useful adjunct to identify multiple defects in the muscular septum.
