Transthoracic Imaging in Pediatrics

Each pediatric echocardiography laboratory has specific protocols for acquiring a complete study of cardiac anatomy in children. Because patient cooperation is needed, all images may not be obtained using standardized imaging planes in young children and infants. Some centers use conscious sedation for patients under a certain age to ensure uniformity of studies. Another option is “video sedation”: child-friendly videos played to distract the patient and allow time to obtain diagnostic images. As long as clear pictures are obtainable, scanning can be performed with the patient sitting in a parent’s lap, feeding, or even in a stroller. This approach substantially decreases the number of patients who must be sedated.

The protocol for a complete study includes views from the four major echocardiographic windows: parasternal, apical, subxiphoid, and suprasternal. Each window provides the image of the heart from a different angle, allowing multiple, corroborating views of the same structures. The image from each window begins from a standard reference view; then a sweep of the heart is made, first with 2D scanning and then with color Doppler. The color Doppler mapping defines the location for pulsed Doppler scanning in each plane. Once pertinent information is obtained, the transducer is rotated 90 degrees to perform an orthogonal sweep. The sonographer and the interpreting physician can reconstruct multiple 2D images into a 3D representation of cardiac anatomy.

Cardiac function and blood flow are calculated from Doppler mapping and from the 2D images. For example, pulmonary and aortic flow are calculated from the mean velocity and diameter of the vessel at the area of interest as follows:

Peak instantaneous gradients are calculated from a simplified Bernoulli equation, using peak flow velocity within the stenotic jet in the following formula, where V is the peak flow velocity measured by spectral Doppler scanning:

This gradient is used to estimate pressures in the different cardiac chambers. Several different methods can be used to quantify left ventricular (LV) function. LV fractional shortening (FS) is a measurement of the percentage of change in LV diameter:

Ejection fraction is similarly calculated, using measured LV volumes.

Echocardiographic examinations are described below for some common congenital heart lesions, with emphasis on information needed to plan surgical intervention and the best techniques to obtain this information.

Atrial Septal Defect

TTE is often sufficient to define the size and location of an atrial septal defect (Fig. 51-1). Pulsed and color Doppler echocardiography identify the direction and amount of shunting at the atrial level. Other findings can confirm the presence of a hemodynamically significant shunt. For instance, right ventricular (RV) volume overload can produce diastolic bowing of the ventricular septum to the left during diastole, with the left ventricle assuming an elliptical shape. Partial anomalous pulmonary veins can be identified by 2D echocardiography and color Doppler, and can be corrected at the time of surgery. Echocardiography is usually sufficient to define the anatomy of the atrial septum and pulmonary veins in infants and small children. For older children and adults, TTE may be needed for full anatomic definition. Cardiac catheterization is not usually needed to evaluate atrial septal defects.