Arrhythmias

An arrhythmia is an abnormal rhythm of the heart, which can cause the heart to pump less effectively. It most often occurs in adults but can also occur in children. Some arrhythmias are not dangerous, while others can be life threatening.

Arrhythmias are classified by the area of the heart where they start: the upper chambers (atria) or lower chambers (ventricles). They can be related to the heart beating too fast (tachycardia), too slow (bradycardia), or in an irregular pattern (fibrillation).

The tachyarrhythmias are classified according to their origin into:

• Supraventricular tachycardia (SVT): This is the most common type of tachycardia in children. It occurs when the electrical signals from the heart’s atria fire abnormally, causing a fast heartbeat. In most cases, they involve an extra pathway inside the heart that entertains an electrical circuit. When this accessory pathway can be identified in the ECG, it is called Wolf-Parkinson-White. Most of these circuits are amenable of treatment by ablation
• Ventricular tachycardia (VT). This is an uncommon, but serious and potentially life-threatening condition. It is caused by a very fast electrical signal that starts in the ventricles. In some cases, it is caused by inherited cardiac conditions

The most frequent cause of slow heart rate (bradyarrhythmia) in children are benign and do not require treatment. In rare circumstances, an abnormally slow heart rate can be related to abnormal conditions as:

• Complete heart block. Heart block occurs when the electrical signal from the atria to the ventricles is blocked. This causes the heart to beat more slowly. Complete heart block may be caused by heart disease or happen after heart surgery.
• Sinus Node dysfunction: Occurs when the sinus node in the heart doesn’t fire properly and the heartbeat slows down. It can sometimes occur in children who have had open-heart surgery. In the case a bradyarrhythmia is causing symptoms in a child, one option to evaluate is the indication of a pacemaker.

How to evaluate an arrhythmia?

• ECG: An electrocardiogram (ECG) is a simple test that can be used to check the electrical activity of the heart by means of sensors attached to the skin. Once the electrical activity is transformed by the machine in patterns of waves printed on paper, it can be analysed by a cardiologist.
• Holter: this is a type of ambulatory ECG performed by a portable device for at least 24 to 72 hours but can be extended to one week. The Holter’s most common use is for monitoring the electrical  activity of the heart. Its extended recording period is sometimes useful for observing occasional cardiac arrhythmias which would be difficult to identify in a shorter period. The monitor is about the size of a mobile phone and you/ your child will need to wear it around your waist or carry it in your pocket. When you return the monitor to the hospital, a cardiac physiologist will analyse the data and produce a report for your doctor. 
• External loop recorder (ELR) is a kind of ECG monitoring system that records cardiac activities of a subject continuously for a long time. When the heart palpitations are not the frequent and nonspecific character, it is difficult to diagnose the disease.
• Implantable loop recorder (ILR) is a small device about the size of a USB memory stick that is implanted just under the skin of the chest and that has a life spam of around 4 years. It can both monitor for abnormal heart rhythm. Recording can be activated in two ways. First, recording may be activated automatically according to heart rates ranges previously defined and set in the ILR by the physician. If the heart rate drops below, or rises above, the set rates, the ILR will record without the patient’s knowledge. The second way the ILR records is through a hand-held “patient activator” whereby the patient triggers a recording by pushing a button when they notice symptoms. The ILR records by “freezing” the electrical information preceding, during and after the symptoms in the format of an electrocardiogram. This information can be either sent immediately to the physician by a central in the patient’s house, or downleaded in the doctor’s office by a special programmer.