Tachycardia refers to a faster than normal heart rate. Normal electrical conduction in the heart starts with the generation of electricity in the sinus node in the upper portion of the right atrium. Electricity moves from the sinus node through the atrium. From there, it is transmitted through the AV node to the ventricles. As electricity passes to the ventricles, the heart muscle contracts.
What is Tachycardia?
Tachycardia simply means a fast heart rate. A normal heart rate in a child varies quite a bit based on age as well as activity level. In a normal teenager, the resting heart rate is typically between 60 and 100 beats per minute. With activity, the heart rate may get as high as 200 beats per minute. During sleep, the heart rate can occasionally drop as low as 30-40 beats per minute.
The most common cause of tachycardia in children and teenagers is sinus tachycardia. This simply means that the sinus node is firing at a fast rate. Most of the time sinus tachycardia is a normal physiologic response. For example, during exercise the heart rate normally increases as the metabolic needs of the body increase. Other conditions which cause an increased metabolic rate may also cause sinus tachycardia, for example fever, infection, or stress. In all of these examples, sinus tachycardia is a normal, expected physiologic response of the body.
Supraventricular tachycardia (SVT) is the most common abnormal form of tachycardia that affects children. SVT is most commonly caused by the presence of an extra conducting pathway from the atrium to the ventricles. In conjunction with the AV node, an electrical circuit is established which allows for rapid transmission of electricity in the circuit. Wolff-Parkinson-White syndrome (WPW) is one specific form of SVT. Less common forms of abnormal tachycardia seen in children include atrial tachycardia, atrial flutter, junctional tachycardia, and ventricular tachycardia.
Because sinus tachycardia is usually a normal physiologic response, most children with sinus tachycardia have no symptoms whatsoever. Children with abnormal tachycardias often feel a sensation of palpitations, or a racing heartbeat. If the heart rate is fast enough, a child may feel dizzy or lightheaded. Rarely syncope or loss of consciousness may occur.
Treatment of tachycardia in children depends on the underlying cause. Physiologic sinus tachycardia requires no treatment whatsoever. Tachycardia due to an abnormal heart rhythm, for example SVT, usually requires either medication or a procedure to cure it permanently.