Supraventricular tachycardia (SVT) are defined as the abnormally fast heart rhythm that originates in the atria or in the atrio-ventricular node (AVN). The two most common SVTs in children are those mediated by an accessory pathway (73%), including Wolff-Parkinson-White Syndrome (WPW) and AVN reentrant tachycardia (AVNRT) (13%). During adolescence the percentage of AVNRT significantly increases. The prevalence of SVTs ranges from 1 in 250 to 1 in 25.000 children, and is the most common alteration in heart rhythm in paediatric patients. Its natural history is in part related to the age and time of initiation of symptoms. Newborns with SVTs have a 30 to 70% chance of being asymptomatic and usually require no treatment, as the tachycardia resolves in the first year. Occasionally, new episodes can be observed at a later age (around 8 years old). In contrast, SVTs persist in around 78% of patients in whom the arrhythmia initially appeared when the child is 5 years old or later. Although pharmacological treatment is an option, catheter ablation with either radiofrequency or cryoablation is associated with high success (>90%) and low complication (<3%) rates.
Ventricular arrhythmias are generated in the ventricular myocardium. They are infrequent in the paediatric age and symptoms can go from dizziness and loss of consciousness to, in some cases, sudden cardiac death. They can be due to genetic alterations such as Brugada or long QT syndromes; they can be secondary to other cardiac alterations or idiopathic, that is, of unknown cause. Depending on the cause, treatment can be pharmacological (catheter intervention) or the implant of an automatic defibrillator (ICD). .