Supraventricular Tachycardia

Supraventricular tachycardia is a condition which causes the heart to beat very quickly (200-300 beats a minute) for an extended period of time. It is the most common cause of a heart rate this fast in children and occurs in one of 250-1,000 kids. But one must first understand how the heart normally beats to understand what happens when it goes awry.

The heart is an amazing organ in that it contains millions of individual cells, yet they all normally contract in a rhythmic manner co-ordinated with each other. This beating is initiated by a natural pacemaker called the sinoatrial node. This SA node, located in the upper half of the heart, generates an impulse at a rate which depends on the age of the child and the level of activity in which the child is involved. Once the impulse is generated, it follows a very specific path toward the lower half of the heart, passing through the atrioventricular node. From there, the impulse travels through the lower half of the heart. This impulse does not travel in the most direct route from top to bottom, resulting in the cells on the top half of the heart contracting just before those on the bottom. This, in turn, allows for efficient pumping of the blood to the rest of the body.

In supraventricular tachycardia (SVT), the impulse takes a more direct route from the top to the bottom of the heart. In the most common type of SVT in children, this impulse travels quickly in a circle from top to bottom but then continues in a route back to where it started, stimulating that impulse all over again. You can see how this would cause a fast heart rate because the impulse is feeding back on itself.

Symptoms depend on the age of the child. In newborns and infants the most common symptom is poor feeding, but other symptoms include fast breathing and lethargy. In older children, a feeling of the heart racing is common, and chest pain, dizziness and fainting may occur. In both sets of children, if you try to take the pulse, you will find it too fast to count.

A procedure called catheter ablation usually cures the problem, especially for those whose SVT is caused by the circuitous impulse pathway described above. This is a procedure in which the cardiologist passes a catheter through the blood vessels into the heart. Then through electrical mapping, the abnormal pathway may be plotted. A small electric current is used to kill the heart cells in that pathway, thus eliminating it.

A child with SVT will only go into the fast heart rate intermittently. When this occurs, most children feel uncomfortable but do not have life-threatening difficulty with the pumping of the blood. There are certain things that can be done at home to get the heart beating correctly. However, they should only be done after a thorough evaluation by a doctor. Most children can be managed well with medication. However, catheter ablation may be most optimal if a predisposing factor to SVT is seen on the EKG, significant life-threatening symptoms occur when the SVT occurs, or the SVT is not controlled by medication. I suggest you talk with your doctor about all the options.