Recording the heart rhythm while the patient is having an episode confirms the diagnosis. This can be done in an emergency room or a physician's office capable of performing electrocardiograms.
In some cases, an "event monitor" is given to the patient to record the heart's electrical activity at home. When the symptom occurs, the monitor is used to record the heart rhythm. The recording can then be transmitted by telephone for review by the cardiologist. Implanted monitors can be used to record rhythms that are brief and infrequent.
The first objective needs to be consultation with your cardiologists regarding the risks of the fast rhythm and the risks and benefits of its treatment. If the fast rhythm has a "benign" course with little impact on daily life, observation may be warranted.
On the other hand, an infrequent fast rhythm that is a cause for concern to either the patient, family, or physician may require therapy. If the fast rhythm recurs despite therapy, the symptoms usually would be the same as before therapy.
The most important thing to learn is taking your child's pulse and knowing the "normal" rate for her / his age. With guidance from your physician, this is an easily acquired skill. The ability to count your child's heart rate can be reassuring to you and helpful to your doctor when making a diagnosis.