Ventricular Septal Defects Workup

Chest radiography, magnetic resonance imaging (MRI), and electrocardiography (ECG) may all provide useful information in the workup of a ventricular septal defect (VSD).

Although cardiac catheterization was a standard part of the evaluation of a VSD in the past, detailed echocardiography is now preferred in most institutions. Echocardiography provides the information required for surgical closure. Cardiac catheterization is used primarily in the following 2 settings:

• Pulmonary hypertension of unknown reactivity
• A small-to-moderate defect with only mild left ventricular (LV) enlargement; in this setting, cardiac catheterization is useful for definitively assessing the pulmonary-to-systemic flow ratio (Qp:Qs), which can assist decision making regarding the need for surgery (though MRI can provide this information noninvasively)

An experienced pediatric cardiologist can accurately assess newly referred patients with murmurs on clinical examination with a sensitivity of 96% and a specificity of 95%.

Chest radiography may reveal the following:

• Small VSDs
• Normal heart size
• Normal pulmonary vascularity
• Moderate or large VSDs
• Increased cardiac silhouette
• Increased pulmonary vascular markings with a prominent main pulmonary artery (PA) segment
• Enlarged left atrium (LA), which is visible on lateral radiographs
• Large VSDs with markedly increased pulmonary vascular resistance (PVR)
• Essentially normal-sized heart
• Right ventricular (RV) hypertrophy with the cardiac apex rotated slightly upward, to the left, and posteriorly
• Markedly prominent main PA and adjacent vessels
• Decreased pulmonary vascularity in the outer third of the lung fields

Two-dimensional echocardiography, with Doppler echocardiography and color flow imaging, can be used to determine the size and location of virtually all VSDs. Doppler echocardiography provides additional physiologic information (eg, RV pressure, PA pressure, and interventricular pressure difference).

Measurement of LA and LV diameters provides semiquantitative information about shunt volume. The size of the defect is often expressed in terms of the size of the aortic root. Defects that approximate the size of the aortic root are classified as large; those that are one third to two thirds of the diameter of the aorta are classified as moderate; and those that are less than one third of the aortic root diameter are classified as small.

The precise location and size of a VSD can be determined by combining subcostal views and apical 4-chamber views with parasternal short-axis and long-axis views (see the images below).

Varying approaches are recommended for different types of VSDs, as follows:

• Perimembranous subaortic VSD – These are best imaged by using the subcostal approach with anterior angulation
• Supracristal VSDs – These are best observed on parasternal long-axis and short-axis views and on sagittal subcostal views; when prolapse of the right aortic cusp obscures the VSD, color Doppler echocardiography is invaluable in defining the location and size of the defect and the degree of secondary aortic incompetence
• Muscular VSDs – For these, all views that show the ventricular septum must be used; color Doppler echocardiography is critical for determining small defects
• Inlet or atrioventricular (AV) canal–type VSD - These are best observed on apical 4-chamber views

Transesophageal echocardiography (TEE) is occasionally used. In the pediatric age group, it is used most often performed intraoperatively to assess the completeness of the repair.

MRI is a useful adjunct tool, but it is infrequently required for the diagnosis of VSDs. As a rule, it is employed only when ultrasonography is not feasible or when ultrasonographic findings are not diagnostic.

However, because MRI data about systemic and pulmonary flows are been well validated and well correlated with catheterization data, one of the indications for the use of MRI is evaluation of a VSD that is judged to be borderline during echocardiography in terms of the level of the left-to-right shunt. For such defects, an MRI-derived Qp:Qs may assist the clinician in making the decision whether to proceed with surgical treatment.

In patients with small VSDs, ECG findings are normal.

In patients with moderate-sized VSDs and with moderate or large left-to-right shunts with volume overload in the LV, LV hypertrophy is the rule. Combined ventricular hypertrophy is common. This may manifest as a large equiphasic midprecordial voltage (> 50 mm) in the midprecordial leads, an event known as the Katz-Wachtel phenomenon. Inlet defects may be associated with left-axis deviation of the frontal plane QRS with Q waves in leads I and aVL.

In patients with large VSDs and equal ventricular pressures, RV hypertrophy is demonstrated. In patients with large pulmonary blood flow, LA hypertrophy is evidenced by biphasic P waves in leads I, aVR, and V₆, with prominent negative deflection in V₁.