Author + information
- Meryl S. Cohen, MD∗ and
- Neil J. Weissman, MD, Chair, Cardiovascular Imaging Section and Leadership Council†
Congenital heart disease (CHD) is present in nearly 1 in 110 live births in the United States and is the most common birth defect. Whereas coronary artery disease is the more common manifestation of heart disease in adults, CHD has wide variability across a diverse population, ranging from fetuses to adults. The severity of CHD is variable, ranging from lesions that do not require intervention to those that require multiple surgical and transcatheter procedures. In more complex cases, lifelong care from a specialized team of congenital heart specialists is required. A critical component of the successful management of a patient with CHD is the ability to accurately image the heart, and thus, a cardiovascular imaging specialist is an essential component of the care team. In this report, we highlight some of the current trends and issues in pediatric cardiovascular imaging.
Setting the Standard
The ability to accurately diagnose myriad congenital heart defects has relied primarily on successful and important advances in imaging. As in adult cardiology, the primary imaging modality used in pediatric cardiology is transthoracic echocardiography. Starting in the 1970s, echocardiography rapidly advanced clinicians' ability to diagnose and assess congenital lesions. The parasternal and apical imaging planes allowed cardiologists to visualize the systemic and pulmonary veins, atrial septum, and ventricular septum and the relationship and anatomy of the outflow tracts and arch. Identifying the liver as a window to the heart in subxiphoid imaging allowed excellent resolution of the components of the atrial septum. This technique is possible because the distance between the abdomen and heart is much shorter in pediatric patients, allowing a unique view of the atrioventricular valves, the ventricular septum, the outflow tracts, and their relationships to one another. Finally, the suprasternal view led to accurate visualization of the aortic arch, branch pulmonary arteries, and pulmonary veins as well as any anomalies of these structures. By the mid-1990s, transthoracic imaging had become so accurate that it was commonplace for children to undergo cardiac surgery solely on the basis of echocardiographic diagnosis. Before these echocardiographic advances, nearly every pediatric cardiology patient was referred to cardiac catheterization for diagnostic evaluation.
The past decade of pediatric cardiology imaging has seen the introduction of more technology-driven modalities. Three-dimensional imaging, tissue Doppler, and deformation imaging have come to the forefront of pediatric echocardiography from a research standpoint. Although these are exciting developments, the methods still have limited clinical use. Pediatric patient characteristics, such as anatomical function, less cooperative children, higher frame rates, and smaller body size, all affect the ability to apply the technology.
In contrast to adult cardiology imaging, multimodality imaging in pediatrics has historically involved echocardiography and angiography, rather than the full spectrum of computed tomography (CT), cardiac magnetic resonance (CMR), and nuclear medicine. Recently, however, CMR has been used to augment echocardiographic findings, when anatomic abnormalities are difficult to delineate. Examples of such anatomic lesions include aortopulmonary collateral vessels in tetralogy of Fallot with pulmonary atresia and intramural course of an anomalous coronary artery. CMR is also used when functional data are required that cannot be provided by echocardiography alone, such as right ventricular ejection fraction, regurgitant fraction and volume, or myocardial perfusion after heart surgery. CMR is often a complementary modality giving a global view of the heart, its anatomy, and its relationship to other structures in the body. It is now used routinely in children with aortic arch anomalies (e.g., vascular rings) and coronary artery anomalies (e.g., anomalous aortic origin of the coronary artery). The timing of such interventions as pulmonary valve replacement after tetralogy of Fallot repair is also based primarily on CMR data. Although cardiac CT has had a smaller role in the pediatric population, it is gaining some popularity. The resolution of cardiac anatomy is exquisite with CT, but there remain limitations to the functional assessment of the heart. As with all patients, precautions are taken to limit radiation exposure.
Although nuclear imaging is rarely used in the pediatric population, it may have a niche as a surveillance tool. Pediatric patients with any coronary issues, such as coronary reimplantation surgery (e.g., arterial switch operation for transposition of the great arteries, surgery after anomalous aortic origin of the coronary artery), Kawasaki disease with coronary artery aneurysms, and, more rarely, homozygous hypercholesterolemia, are often referred for nuclear imaging to assess and monitor the coronary arteries. Unlike in adult cardiology, nuclear testing is usually performed by a radiologist.
Training and Laboratory Requirements
Although these techniques are increasingly used, pediatric cardiologists who complete 3-year fellowships are rarely competent in CMR or CT, and additional training is almost always required if they want to apply these techniques in clinical practice. Pediatric cardiology fellows spend most of their imaging rotations learning views that highlight the structural rather than functional components of the heart. Additionally, great emphasis is placed on the initial description of congenital heart defects. Imagers are required to record significant detail of all structures using 1 of 2 methods (Van Praagh or Anderson) of approach to nomenclature. Echocardiography reports generally list cardiac diagnoses on the basis of this anatomical description. Unless stress echocardiography is used, there typically is no requirement to describe regional wall motion abnormalities.
Because there are differences in the techniques, technology, and training of pediatric cardiologists, the accreditation of pediatric echocardiography laboratories also has specific considerations. High-volume laboratories are generally hospital based. These laboratories require sedation protocols needed for uncooperative children in the age range of 3 months to 3 years. Highly-trained nursing staff members or even anesthesiologists are often needed to perform conscious sedation safely and effectively.
Transesophageal echocardiography is performed in the operating room to assess the repair of CHD or in the cardiac catheterization laboratory to guide interventional procedures. Diagnostic transesophageal echocardiography is rarely performed, because the acoustic windows in children tend to be quite acceptable.
The Future of Pediatric Cardiology Imaging
As in adult cardiology, the explosion of new technologies and techniques promises improved diagnostic abilities for the pediatric cardiology and CHD populations. Future directions in pediatric cardiovascular imaging will likely include hybrid imaging and improved 3-dimensional echocardiography. Using complementary modalities to provide anatomic as well as functional assessments could potentially improve diagnosis and care. CMR images will be able to overlay angiograms so that interventional cardiologists can visualize the anatomy as they perform procedures (such as device closure of septal defects or placement of stents in precarious locations). It may be possible to use fusion imaging to help electrophysiologists perform ablations without damaging valves, the coronary sinus, or the pulmonary veins. All this will be achieved with less radiation exposure to patients.
Three-dimensional printers can be very useful in complex congenital disease by creating an anatomic copy of a patient's heart and thus displaying the anatomy from any view. Pediatric cardiothoracic surgeons will then be able to readily identify where to place complex baffles to separate the systemic and pulmonary circulations and will be able to determine ahead of time whether such baffles will result in obstructions to flow or damage to a valve. Three-dimensional echocardiography could potentially overlay angiograms to identify the mechanisms of atrioventricular valve regurgitation for catheter-directed or surgical valvuloplasty. Moreover, 3-dimensional echocardiography will provide accurate assessment of right ventricular size and function so that CMR may not be needed to determine the timing of interventions. As the technology improves, 3-dimensional transesophageal echocardiographic probes will be small enough to be used in neonates to help with procedures such as balloon atrial septostomy and atrial stent placement.
Early noninvasive diagnosis of CHD has made astounding progress since the first B-mode images were acquired in the 1970s. Techniques, technology, and training have been powerful assets for these advances. Now, as the population of adults with CHD increases, the cross-training of adult congenital and pediatric cardiologists with imaging skills will be critical to ensure that an appropriately trained workforce is available to care for the nearly 3 million children and adults living with CHD.
To address the clinical gap within pediatric cardiology, the American College of Cardiology's (ACC) Adult Congenital and Pediatric Cardiology Member Section has championed efforts to develop national standards in pediatric cardiology and CHD imaging. The ACC, American Society of Echocardiography, and American Academy of Pediatrics appropriate use criteria in pediatric echocardiography are expected to offer the pediatric community guidance on when to refer pediatric patients without diagnosed CHD for echocardiography. Additionally, the ACC's Adult Congenital and Pediatric Cardiology Member Section is proposing candidate quality metrics to promote internal quality standards and create a structure for collaborative quality improvement across the field.
The ACC's member sections offer a powerful forum for collaboration across specialties. In pediatric and CHD imaging, 2 focus areas overlap and are helping to drive quality standards and develop a specialty-trained workforce to help the CHD population.
- American College of Cardiology Foundation