The resting heart rates of infants, children, and adolescents are higher than those of adults, and there is more heart rate variability with respiratory changes (sinus arrhythmia, Table 23.2). The image acquisition window of current-generation CT scanners is as low as 75 ms, allowing coronary imaging even at higher heart rates. Coronary artery imaging is recommended in pediatric patients for evaluation of potentially malignant coronary artery anomalies, after surgical manipulation or reimplantation, and for evaluation of stenosis or coronary pathology in patients with a history of Kawasaki disease, systemic inflammatory disease, or Williams Beuren syndrome (aortic or pulmonary artery stenosis).

Beta blockade and other medication protocols have been used safely in healthy children to decrease the heart rate and improve the quality of coronary imaging. For patients with chronic heart failure or in those who are critically ill, beta blockade may be clinically contraindicated (Chap. 6). The use of premedication must be tailored to individual patients and their current clinical status.

The newest-generation volumetric or high-pitch scanners can acquire the scan range of a pediatric thorax in one heart beat, or a fraction of a second, which has reduced anesthesia and intubation needs in young patients. Many scans can be performed during free breathing without loss of image quality due to motion artifacts. For some older-generation scanners with image acquisition over several seconds, intubation or sedation may be required to obtain a scan without respiratory motion artifacts. The use of anesthesia and sedation will be dependent on the scanner available at each institution and the amount of detail required from the CT scan.

Many types of peripheral access can be used for cardiac CT scans in patients with congenital anomalies including peripherally inserted central catheter (PICC) lines, umbilical venous lines, peripheral intravenous (IV) lines, and central venous lines. In the presence of intracardiac shunting, elimination of air bubbles in the injection is particularly important to avoid potential arterial emboli. Low flow rates are recommended when using a 24- or 22-gauge IV access. Careful observation of the IV site during a saline injection is recommended to confirm patency before the contrast agent is injected. Safe power injection through 24–18 gauge IV lines has been reported in pediatric patients. The contrast injection rate through a 24-gauge IV line is typically 0.5–1.0 ml/s and up to 1.5–2 ml/s through a 22-gauge IV access (Table 23.3).

The total contrast agent volume used for pediatric CT angiography is typically 1–2 ml/kg. For pulmonary or arterial angiography without intracardiac mixing, the IV line may be placed in any extremity and an automatic trigger used for image acquisition. A biphasic injection protocol can be used for simultaneous opacification of right- and left-sided cardiac structures.

Every pediatric CT scan must be adjusted to deliver the lowest radiation dose to obtain a diagnostic image according to the “as low as reasonably achievable” (ALARA) principle. Familiarity with the doses delivered with different scan modes is necessary and allows choosing the scan mode with the least risk for each specific indication. CT scanner output should be adjusted to the patient’s size. Using dose reduction techniques allows mSv or sub-mSv imaging for many pediatric indications, including coronary artery imaging.

For anatomic scans, high-pitch or the volumetric scan mode may be used on latest-generation scanners. On older-generation scanners, anatomic scanning is most commonly performed without ECG triggering.

Coronary artery and functional imaging require ECG triggering on all scanner platforms. Several different scan modes are available for coronary artery imaging. The lowest dose technique deemed adequate for the individual patient’s heart rate should be used.

For pediatric cardiovascular CT, no general recommendation for kV and mAs settings can be provided. For dose comparison, the dose length product (DLP) should be used. In our experience, a DLP as low as 4–8 mGy*cm (70 or 80 kV) is sufficient for imaging a baby weighing 3–4 kg. Only a minor increase in DLP is necessary with increasing weight, as the thoracic diameter stays rather constant during the first years of life. The most common indication for CT angiography in the neonatal CHD population is for evaluation of aortic or pulmonary artery pathology or for characterization of complex systemic and pulmonary venous anomalies prior to intervention. Many postoperative patients will have metallic implants and devices that degrade image quality of MRI. CT is also valuable for coronary artery assessment in patients with a history of Kawasaki disease aneurysm and for assessment of bileaflet mechanical valve function.

The most common congenital anomalies are atrial (7%) and ventricular septal (31%) wall defects (Fig. 23.1). However, the role of CT in patients who are referred for preoperative evaluation of ventricular or atrial septal wall defects is limited. Echocardiography and MRI are the main diagnostic modalities for these lesions.

Congenital anomalies of the aorta are one of the most frequent cardiovascular malformations. They include a wide spectrum of diseases (List 23.1) ranging from patent ductus arteriosus (Fig. 23.2, 5–10% of all CHD) to aortic coarctation (8–10%, Fig. 23.3). The initial diagnosis is usually established by echocardiography. Blood pressure difference between the upper and lower extremity is used to determine the pressure gradient unless there is an aberrant subclavian artery that does not allow a pre-coarctation pressure estimate. Doppler echocardiography is helpful in these cases, and catheterization is rarely required prior to surgical intervention for aortic coarctation at most centers. Noncritical stenosis or critical stenosis with well-developed collateral flow to the descending aorta is often detected in grown-ups who present with arterial hypertension and have blood pressure differences between arms and legs. Clinical indications for follow-up examinations are re-coarctation (<3%, higher when operated on in infancy) and postoperative aneurysms (24% after patch angioplasty) or dissection (5–50% after patch angioplasty, Fig. 23.4). Because it lacks radiation exposure and allows functional assessment (e.g., flow quantification), MRI is the preferred test in suspected coarctation (Fig. 23.5). As patients grow older, MRI may gain an increasing role as the acoustic window for echocardiography becomes poorer with age. CT has an indication in the follow-up of patients with coarctation who have stents, as the intraluminal visualization of stents is excellent (Fig. 23.6). In complex aortic arch abnormalities (i.e., double aortic arch), surgeons prefer to have a three-dimensional display of the anatomic relationship between the trachea and the vascular structures. This information can be nicely provided by CT, even in critically ill children. A potential vascular ring associated with a right aortic arch, an aberrant left subclavian artery, and a left-sided ductal ligamentum are common and may be detected incidentally or cause pulmonary pathology. Evaluation of the airways relative to the vessels can be crucial in determining the clinical significance of the finding.

Echocardiography is excellent for definition of the pulmonary valve and proximal pulmonary arteries, but is inadequate for distal pulmonary artery evaluation. CTA is well suited for detection of an absent pulmonary artery, a pulmonary artery arising anomalously from the aorta (Fig. 23.9) or aortopulmonary collateral arteries, and peripheral stenosis associated with certain genetic syndromes (Fig. 23.10) and for visualization of both the aortic and pulmonary arterial portions of the ductus arteriosus.