Anatomy: A rigorous and systematic approach to anatomy of native CHD and of repaired CHD is very different from heart disease in the adult. Cardiac segments (atria, ventricles, and great vessels) may not be in the proper position and connections between them may be altered (as in transposition of the great arteries, where the aorta is connected to the right ventricle and the pulmonary artery is connected to the left ventricle). Venous anatomy too may not be connected properly (such as total anomalous pulmonary venous connection, where the pulmonary veins are connected to any structure other than the left atrium). Communications may present where they should not be (e.g., ventricular septal defect where there is a communication between the right and left ventricles), and some cardiac structures might not even be present or present in a markedly hypoplastic form (e.g., hypoplastic left heart syndrome, where the left ventricle is markedly hypoplastic). As surgery and catheter-based therapies play such an important role in CHD, the postinterventional anatomy must be familiar to the physician performing the CVMR examination.

Physiology/function: In the world of the infant and child with CHD, there are many times that a unique physiology is present and a result of the altered anatomy. Evaluation of shunts (e.g., in a patient with a truncus arteriosus referred to CVMR, where one great vessel arises from the heart to give rise to the systemic, pulmonary, and coronary systems) or the complex physiology of transposition of the great arteries plays a critical role in the assessment of any disease entity in pediatrics and has little parallel in the adult world. In addition, assessment of ventricular function in ventricles with strange and unusual shapes are routine in the practice of CVMR in children (e.g., L-looped ventricles which have a “left sided” right ventricle and a “right sided” left ventricle) and demand unique solutions. Assessment of the postoperative physiology where the surgeon, for example, creates an anastamosis between the cava and the pulmonary artery (when repairing a single ventricle) must be dealt with. CVMR must be adapted to fit these needs and the physician interpreting the study needs to understand the complex physiology. Even without gross anatomical alterations, function can be severely altered such as in an infant with a left ventricular aneurysm or with a dysplastic tricuspid valve (Figs. 9.1 and 9.2).

Technical challenges: Infants and children present a unique challenge in the world of CVMR; they require increased spatial resolution because of their small size and increased temporal resolution because of their high heart rates. When imaging adults, tradeoffs can be made between those two competing parameters to make imaging quicker and simpler without sacrificing diagnostic accuracy. As pulse sequences were generally designed to image adults, these tradeoffs can be performed in infants and children to a limited degree. In addition, because of the need for increased spatial resolution, signal-to-noise ratio (SNR) considerations play an important role and are always taken into account. Further, children under 7 to 9 years of age usually require sedation which can make sequences designed for breath-holding useless. Since breath-holding is the mainstay of adult CVMR, “work-arounds” have been developed to successfully image the pediatric patient. These CVMR modifications must be understood for children to be imaged properly.

As alluded to above, sedation and general anesthesia for young patients must be administered to allow a child to remain motionless for a 45- to 60-minute scan; this has recently become less of an issue with the advent of the “feed and swaddle” technique which has been successfully used in infants at 6 months of age (17) (Fig. 9.1). In addition, even though they may have the cognitive ability to hold still, cooperation by the preteen or teen may be problematic (e.g., breath-holding).

As surgery and catheter-based interventions play an important role in CHD, wires, stents, coils, and clips may all cause artifacts if they are near the structure(s) of interest.

As many critically ill infant and children are treated in the intensive care unit, the lack of portability of CVMR is certainly disadvantageous; moving the patient to the CVMR suite can be a challenge.

Children with arrhythmias, especially after surgery, may not allow proper triggering while other patients may have bizarre T waves or bundle branch blocks which may not have the same effect. Although this can be problematic, it is less of an issue now that “single shot” CVMR, “real time” cine CVMR, and sequences with “arrhythmia rejection” are realities.

5. Pacemakers and ICDs are still a relative contraindication and patients with them usually do not undergo CVMR, although there is some data to suggest that this may be safe (18).