Several tests can help your doctor diagnose an arrhythmia. Identifying, or documenting, an arrhythmia requires recording the heart's activity using an electrocardiogram (ECG or EKG).

Watch an animation of an electrocardiogram (ECG)

Small patches or stickers, called electrodes, are placed on different parts of the body. One is put on each arm and leg and several across the chest. They don't hurt. With various combinations of these electrodes, different tracings of the heart's electrical activity can be made and permanently recorded on paper or in a computer.

Three major waves of electric signals appear on the ECG. Each one shows a different part of the heartbeat.

• The first wave is called the P wave. It records the electrical activity of the atria.
• The second and largest wave is the QRS wave. It records the electrical activity of the ventricles.
• The third wave is the T wave. It records the heart's return to the resting state.

Exercise test — ­­ It may be important to know if exercise makes an arrhythmia worse. To test this, your child will walk and run on a treadmill — or ride a stationary bicycle — while the heart rate and rhythm are monitored. This is painless, but your child must cooperate.

In Holter monitoring, electrodes are taped to the chest. The wires are connected to a portable, battery-operated recorder that can run for 24 to 48 hours. Your child can do most normal activities while being tested. Then the tape is analyzed on a computer that rapidly identifies rhythm disturbances.

See an illustration of Holter monitoring

Trans-telephonic monitor/event recorder —  Sometimes arrhythmia symptoms happen infrequently, or pass so quickly that you can't get to a doctor or hospital. In these cases, a "transient event monitor" may be used. These small recorders are sent home with a person for a month or two. When your child has symptoms, attach the recorder with bracelets, finger clips or patches under the arms. The ECG will be recorded and stored. When it's convenient, you can transmit the ECG by phone to the cardiologist to be analyzed.

Echocardiogram —  Echocardiography works much like sound waves used to study solid objects in the sea (sonar). You may only think of ultrasound being used to monitor a baby's growth, but ultrasound waves can also show the heart's size, structure and motion. This simple, painless test often provides valuable information about a heart with an arrhythmia.

See an illustration of an echocardiogram

Tilt test —  A tilt test may be advised for children who've had recurrent fainting spells (syncope). This test shows how your child's heart rate and blood pressure respond to a change in position from lying down to standing up. In this test, an intravenous line (a small plastic tube in a vein) is usually started. A catheter also may be placed in the artery to monitor blood pressure. In some cases medications are given through the intravenous line.

If a cause of the fainting spells is found, doctors give medications through the intravenous line to help prevent the episodes. This information will help your child's doctor find the best way to treat these episodes.

Esophageal electrophysiologic procedure —  In some situations, your cardiologist may advise doing an esophageal electrophysiologic procedure. This is used to diagnose or treat the type of tachycardia your child has. A thin, soft, flexible plastic tube will be inserted into your child's nostril and positioned in the esophagus (the tube that connects the mouth and stomach). Because the esophagus is close to the heart's upper chambers (atria), an ECG recording there gives more precise information than a regular ECG. An electrical stimulator may be used to make the heart beat faster to try to restart your child's arrhythmia. This helps your child's doctor make the right diagnosis.

During this procedure certain medications may be tested to find the most effective one. This procedure also may be done to temporarily stop certain types of arrhythmias.

Intracardiac electrophysiologic procedure —  Sometimes it's necessary to study the heart's electrical system with an intracardiac (within the heart) electrophysiologic procedure. In this, one or more long, thin tubes (catheters) is placed into the large blood vessels in the legs, arms or both. Then the tips of the catheters are moved into the heart. Once there, they record electrical signals from the normal electrical system. This gives much more precise information than an ordinary ECG.

During these studies, the heart is stimulated to beat rapidly or irregularly. The heart's response to this — and the way electricity moves around the heart during a tachycardia —  helps the cardiologist diagnose the nature of an arrhythmia.

Watch an animation of electrophysiology studies

This content is reviewed regularly. Last updated 01/16/09.