Pediatric Atrial Septal Defects Workup

In general, no specific laboratory studies are available to aid in the diagnosis of an atrial septal defect (ASD). Determinations of brain natriuretic peptide (BNP) or pro-BNP levels may be helpful in infants and in some children with large atrial septal defects and congestive heart failure (CHF) when their clinical symptoms are equivocal. BNP levels are elevated in patients with ventricular volume overload and CHF.

Plain radiographic findings in atrial septal defect are nonspecific but include right atrial and right ventricular dilatation, pulmonary artery dilatation, and increased pulmonary vascular markings. In general, an enlarged right atrium leads to overall cardiomegaly on the anteroposterior (AP) radiograph. Pulmonary artery dilatation results in a prominent hump between the aortic knob and the left ventricular contour on the AP radiograph. Although pulmonary vascular obstructive disease (PVOD) is rare, if it develops, the main pulmonary artery becomes large and the lung fields become oligemic.

Two-dimensional and Doppler echocardiography revolutionized the diagnosis of atrial septal defects. These studies can effectively reveal both the extent of the defect and provide clues to the degree of left-to-right shunting. In small patients, the anatomy is observed especially well on subcostal views. The anomaly called deviated superior attachments of septum primum is reliably observed with only the modified subcostal left oblique view.^[9]

In older children, large adolescents, or adults, transesophageal echocardiography (TEE) may be required to document an atrial septal defect because of limited transthoracic echocardiographic windows. This is particularly true if sinus venosus and unroofed coronary sinus type atrial septal defects are present. TEE is useful in recognizing and further elucidating pulmonary venous abnormalities associated with sinus venosus defects and ruling out partial anomalous pulmonary venous return in general. TEE may also be useful in small children with poor echocardiographic windows, but the procedure requires sedation and specific expertise. TEE is very useful in further characterizing the size and location of the defect at the time of attempted catheter-based device closure, as well as assisting the interventional cardiologist with balloon-sizing of the defect and device placement.

Cardiac MRI has the advantage of not being limited by acoustic windows and offering imaging in essentially any plane. It may be useful in the diagnosis of sinus venosus or coronary sinus defects in both children and older individuals. In experienced hands, cardiac MRI can easily depict anomalous pulmonary venous drainage associated with sinus venosus defects and a left superior vena cava, which is often associated with coronary sinus defects.^[10] In general, older children do not require sedation for cardiac MRI (this is generally not the case with transesophageal echocardiography). Cardiac MRI can also be used to calculate the effective left to right shunt (Qp:Qs) and quantitate right ventricular function and volumes.^{[11, 12]}

It generally should not be used in attempts to further define atrial septal anatomy when entertaining the possibility of percutaneous device closure because transesophageal echocardiography defines the margins of the ASD much more effectively. Additionally, cardiac MRI is not readily available at all centers and requires a considerable amount of technical expertise, especially when imaging pediatric patients.

CT angiography is a quick and effective means to identify pulmonary venous abnormalities associated with sinus venosus defects or to rule out suspected anomalous pulmonary venous return identified on echocardiography prior device closure. It has the advantage of providing a comprehensive assessment of the pulmonary arteries and the lung parenchyma in patients in whom interstitial/chronic lung disease or pulmonary artery hypertension is an added concern.^[11] In children, similar to cardiac MRI, it is not an adequate modality to evaluate the atrial septal anatomy when assessing for the possibility of percutaneous closure. However, ECG-gated cardiac CT scanning has been demonstrated as an accurate method to determine intraatrial shunting in adults.^[13]

Some data support a stronger correlation between TEE-derived atrial septal defect dimensions and CT-derived dimensions, when compared with transthoracic echocardiographic dimensions, especially for larger atrial septal defects in the pediatric population.^[14] This has potential relevance if there is concern regarding the success of a catheter-based approach, in the face of a large atrial septal defect. However, CT angiography comes with the added adverse effect of radiation, and care must be taken to find the best imaging modality at the lowest possible risk. Newer version CT scanners can be adjusted to provide lower radiation doses for children, while not sacrificing very short scanning times.

In some instances, cardiac catheterization is needed to provide further hemodynamic information prior to intervention. Pulmonary-to-systemic flow can be accurately determined when symptoms and results of other imaging modalities do not correlate. Additionally, calculations of pulmonary vascular resistance can be performed if pulmonary hypertension is a concern, and measurements of pulmonary vein saturations can aid in the evaluation of primary pulmonary diseases that might be confounding the clinical picture. Ideally, a mechanism should be in place to perform percutaneous device placement if the defect is suitable for closure at the time of the hemodynamic catheterization.

ECG most commonly demonstrates right-axis deviation, right ventricular hypertrophy, and an rSR' or rsR' pattern in the right precordial leads. The QRS duration is usually normal. However, the ECG may be normal, especially in infants and in young children with small defects (see the image below).

Left-axis deviation with a superiorly oriented counterclockwise frontal-plane loop suggests an ostium primum atrial septal defect (see the image below).

All types of atrial septal defect can result in prolonged PR intervals. This prolongation of internodal conduction may be related to the increased size of the atrium and a long internodal distance (which is a result of the defect).

Cardiac catheterization is rarely necessary in the preoperative evaluation of a child with atrial septal defect. Cardiac catheterization may be necessary if pulmonary hypertension is suggested to document PVR and to assess the response of PVR to vasodilator substances. It may also be necessary to evaluate associated lesions, especially in patients with more than one left-to-right shunt.

Findings on catheterization include a step-up in oxygen saturation from the superior vena cava to the right atrium (usually >10%), slightly increased right ventricular pressures, a small pressure gradient across the pulmonary valve (due to increased flow across a fixed valve orifice) and normal to mildly increased pulmonary artery pressures. If a large defect is present, the mean pressures in the right and left atria are identical.

The above being said, catheter-based interventions for the closure of selected secundum ASDs have become most common in pediatric patients. Although catheterization is rarely needed for diagnosis, it may be useful from a treatment standpoint. See Treatment for further details.