Hi Laura,
Welcome to Healthcare Magic forum.
Supraventricular tachycardia or SVT is the most common type of arrhythmia seen in children. The most common type of SVT seen in young children is Wolff Parkinson White Syndrome. Usually, the only electrical connection between the upper and lower chambers is the AV node. Children with SVT usually have an extra pathway which connects the upper and lower chambers of the heart. Most of the time, this extra pathway does not affect the heart rhythm. But if there is an early heart beat (called a premature atrial contraction — PAC, or premature ventricular contraction — PVC), the impulse may travel down to the lower chambers using the normal pathway, the AV node, causing the heart to beat, and travel back up the extra pathway to the atria. The impulse then continues going around this circuit, driving the heart at a very fast rate. The normal heart rhythm can be resumed when the electrical loop is blocked anywhere along its route.
Another type of SVT is atrial nodal re-entrant tachycardia which arises due to presence of an extra focus or pacemaker in the atria. This discharges faster than the SA node which is the pacemaker in normal hearts.
This can be precipitated by caffeine and certain drugs such as decongestants, inhalers for asthma and thus these patients are advised to avoid taking these medications.
Definitive treatment for WPW syndrome includes radiofrequency ablation where thermal radiofrequency energy is used to ablate the extra pathway. However treatment choice frequently depends on age/size of the patient, the frequency and severity of symptoms, treatment effectiveness for a particular patient, whether the child wants to play competitive sports, and child/family preference.
Take care.

Hi......Laura....,
welcome to HCM...,
Thanks for query...,
4 month old boy have SVT...,
several episodes shows severity.....
In this age main causes are.......1) Thyroid problem ( to evaluate)
2) Lung disease......pneumonia..,
pulmonary emboli...
(blood clots migrating to lung arteries....
from else where ...hence rule out it...
3) Structural abnormality(WPW Syndrome)
in which extra electrical tissue sets up abnormal
electrical circuits...
Treatment is favourable....1) Halting the acute episode...,
2) preventing new ones...,
Hence good treatmentis available.....consult Cardiologist and go accordingly...o.k.good luck....