An arrhythmia is an abnormal rhythm of the heart. In an arrhythmia, abnormal electrical signals through the heart muscle may cause the heart to beat too fast (tachycardia), too slow (bradycardia), or irregularly. When the heart doesn't beat normally, it isn't able to pump blood to the body as well. That means the brain, lungs, and other organs may not get enough blood. And the organs can't work as well and may become damaged.

Arrhythmias in children include:

  • Long-Q-T syndrome (LQTS). This is a condition passed from parents to children (inherited). It usually affects children and young adults. Many children have no symptoms, but fainting is common in those who do.
  • Premature atrial contraction (PAC) and premature ventricular contraction (PVC). PACs or PVCs are abnormal beats that start in the upper chambers of the heart (atria) or the lower chambers of the heart (ventricles). They are common in children and adolescents. Often, they are considered completely normal and harmless.
  • Sinus tachycardia. A fast heart rate that occurs with fever, excitement, and exercise. It is normal.
  • Supraventricular tachycardia (SVT), paroxysmal atrial tachycardia (PAT), or paroxysmal supraventricular tachycardia (PSVT). This is the most common tachycardia in children. It involves the atria and ventricles. It is not life-threatening. Treatment may be needed if it happens often or lasts long.
  • Wolff-Parkinson-White (WPW) syndrome. This is an abnormal electrical signal that gets to the ventricle too quickly. A fast heart rate is a common symptom. Or a child may not have symptoms. Sudden cardiac death may occur.
  • Ventricular tachycardia (VT). This is a life-threatening arrhythmia. It may be from serious heart disease. It is caused by a very fast electrical signal from the ventricles. A child may feel weak, tired, dizzy, or may faint (syncope). He or she may also feel his or her heart beat (palpitations).
  • Sick sinus syndrome. The heart's natural pacemaker (sinus node) doesn't work as it should. A child usually has both bradycardia and tachycardia. It may occur in children who have had open heart surgery. A child may not have symptoms. A child with symptoms may be tired or dizzy, or may faint.
  • Complete heart block. The electrical signal from the upper to lower chambers is blocked. The heart usually beats considerably more slowly. This problem may happen after heart surgery or be caused by heart disease. It may cause a child to faint.