Accompanying advances in the treatment of arrhythmias in adults, there have been remarkable advances in the treatment of arrhythmias in children and congenital heart disease. Wolff–Parkinson–White syndrome can now be safely ablated in children. Patients with severe congenital heart disease also are now surviving into adulthood, leading to new problems of arrhythmias and sudden death. Recently, a conduit puncture and ablation technique was developed for treating arrhythmias after Fontan surgery that has resulted in improved outcomes.

Long-QT syndrome (LQTS) is an inherited heart disease characterized by QT-interval prolongation and ventricular arrhythmias, leading to syncope and sudden cardiac death. In Japan, school-based routine electrocardiogram screenings have found a large number of asymptomatic individuals. In approximately 50% of clinically diagnosed cases, variations in >17 LQTS-causative genes have been identified. A significant contributor to the triggers of cardiac events and different aspects of gene-specific therapies is genotype. Therefore, an accurate diagnosis is crucial. Various phenotypes can be identified by T-wave morphology and the corrected QT (QTc) interval in the recovery phase of exercise stress tests. Genetic testing should be performed in patients with a clear phenotype, and it is important to confirm that the genotype is compatible with the phenotype. The main factors found to be associated with cardiac-event risk were sex, QTc, variant type/location, and history of cardiac events. There was also a significant effect of age on the QTc interval and cardiac-event risk during childhood and adolescence.

Patients with various heart diseases require treatment in the pediatric intensive care unit. However, hemodynamics, anatomy, and cardiac function vary widely. It is crucial to understand the basic concepts of circulatory physiology for perioperatively managing patients with severe heart failure or complex heart disease setting. Although this knowledge alone will not ensure a positive outcome, aiming for “physiologically correct” circulatory management is recommended. A cardiac care unit would provide the expertise needed for management.

Therapeutic strategies must be based on appropriate evaluation in pediatric pulmonary hypertension because of the diversity of its pathophysiology. Pulmonary arterial pressure is expressed as the product of pulmonary blood flow and pulmonary vascular resistance (R); however, pulmonary circulation exhibits high arterial capacitance (C), so circulatory resistance is the impedance defined as the combined resistance of R and C. Typically, C is expressed as the pulmonary stroke volume divided by the pulmonary artery pulse pressure, and the product of R and C is the time constant τ, which reflects the temporal changes in the pulmonary blood capacity. The time constant τ depends on age, heart rate, and left-atrial pressure. When the hyperbolic curve-plotting RC (RC coupling) is assessed, alterations in the C value in response to the R value are non-negligible in practical clinical settings. Therefore, C more sensitively reflects alterations in the pulmonary vascular beds. The pathophysiological factors of pediatric pulmonary hypertension are classified into left-to-right shunt due to congenital heart disease, left-heart obstructive disease, or left-heart diastolic dysfunction, alveolar hypoxemia, pulmonary vascular obstructive disease, and pulmonary vascular maldevelopment. The extent to which these five pathological factors contribute to pulmonary hypertension must be known. Consequently, it will be helpful to observe alterations in pulmonary arterial pressure as well as RC couplings while modifying each pathological factor during the appropriate evaluations in pediatric pulmonary hypertension.

Cardiac magnetic resonance imaging (MRI) is a three-dimensional modality for evaluating the beating heart, not only by anatomy but also by blood flow dynamics even in the complex cardiovascular system of congenital heart disease. Four-dimensional (4D) flow MRI is particularly useful for assessing cardiac anatomy and function by three directional ECG-gated cine phase contrast at the same time. The advantages of 4D flow MRI are free and systematic access to all intracardiac and extracardiac lesions, which are often difficult to visualize by echocardiography. The most important feature of 4D flow MRI is the quantitative assessment of blood flow, including shunt flow ratio and valve regurgitation volume. In cardiac surgery for congenital heart disease, a recent advance in 4D flow MRI is computational fluid dynamic (CFD) simulation combined with computational graphics. This CFD simulation can help prospective surgical design and treatment strategy as well as predict perioperative management and postoperative hemodynamics.

The cardinal feature of cardiovascular magnetic resonance (CMR) imaging is its non-contrast, non-radiative, and non-invasive nature. CMR facilitates repeated imaging over time, which is particularly suitable for pediatric cardiology patients because echocardiography becomes increasingly challenging with patient growth. Among its various imaging techniques, two dimensional (2D)-Phase Contrast (2D-PC) CMR possesses a unique function unavailable in other modalities: it can measure blood flow in any region of interest. This article provides a detailed exposition of 2D-PC CMR. We first discuss the fundamental principles and practical aspects of scanning and then extensively discuss its clinical applications. Additional clinical applications of 2D-PC CMR hold great promise.

Patients with total anomalous pulmonary venous connection accompanying pulmonary venous obstruction require early interventions soon after birth. We experienced the case of a preterm baby with infracardiac total anomalous pulmonary venous connection and an obstructive vertical vein who underwent preemptive stent implantation and repetitive stent dilatation followed by elective corrective surgery. The patient was delivered at 32 weeks and 5 days of gestation and birth weight 1,284 g. Systemic oxygen saturation was 86％, and a chest X-ray showed pulmonary congestion. At the age of 4 days, a stent was placed at the obstructive ductus venosus, which required transcatheter stent dilatation due to in-stent stenosis at the age of 29 and 38 days. At last, intracardiac repair was performed with weight of 1,849 g at the age of 57 days. Stent implantation for an obstructive vertical vein is feasible and effective even in preterm or low birth weight infants with total anomalous pulmonary venous connection and an obstructive vertical vein.

Among heterotaxy syndromes, asplenia is often associated with complex congenital heart disease. Asplenia also increases the risk of developing invasive bacterial infections, and recently, prevention has become more important than was earlier thought. The patient, a 7-month-old girl, had undergone abdominal surgery for anal atresia, duodenal obstruction, and Meckel’s diverticulum. She had experienced repetitive infection-related wheezes and then developed coughing, wheezing, and worsening symptoms, so she was urgently admitted with pallor and cyanosis at night. She was treated with inhalational beta-adrenergic agonists and corticosteroids for bronchial asthma, but because her symptoms persisted, she required a high-flow nasal cannula (HFNC). After administering HFNC therapy, her symptoms gradually improved, so she was weaned from HFNC on post-admission day 9 and discharged on day 11. To elucidate the etiology of her wheezing, a computed tomography (CT) scan was performed, which revealed bridging bronchus, bronchial stenosis, and asplenia. Echocardiography and CT revealed an atrial septal defect with a very trivial left–right shunt, right aortic arch, and anomalous origin of the left-subclavian artery. A hemogram on admission revealed Howell Jolly bodies (1％). She was diagnosed with asplenia without complex congenital heart disease and started on antibiotic prophylaxis. This case highlights the importance of understanding that asplenia can manifest in the absence of complex congenital heart disease and require adequate precautions against invasive bacterial infections in patients with asplenia.