The heart’s electrical system

The heart has four chambers. The two lower chambers are called ventricles. The two upper chambers are called atria. The heart has an electrical system. It sends signals to trigger the heartbeats. The sinoatrial (SA) node is in the right atrium. This node is the heart’s own pacemaker. It creates and sends the signal that starts a heartbeat. The signal then moves through the atria. This causes them to contract and to make blood cross the heart valves toward the ventricles. The signal then travels to the atrioventricular (AV) node. This node stops the signal briefly so that the blood can fully enter the ventricles. Then the node sends the signal into paths called bundle branches. The bundle branches pass the signals to the ventricles at nearly the same time. This allows them to squeeze and pump blood to the lungs and body. This cycle completes a heartbeat. After each heartbeat, the heart recharges, and all chambers relax so they can fill with blood again. Then the cycle starts again.

Causes of a cardiac arrhythmia

An arrhythmia happens when the normal pattern of electrical activity of the heart is changed. This may be due to a problem with the electrical system. There are several causes of this. They can include:

• Congenital heart defects. These are structural heart problems present at birth.

• Damaged heart muscle (cardiomyopathy)

• An isolated heart problem such as an abnormal extra electrical pathway in the heart

• Changes after heart surgery

• Infections that damage the normal conduction system

• Chemical imbalances

• Medicines

Symptoms of a cardiac arrhythmia

Symptoms may vary. It depends on whether the rhythm is too fast or too slow. Symptoms may include:

• Lightheadedness, or fainting or passing out (syncope)

• Tiredness

• Chest pain

• Sweating

• Trouble breathing or rapid breathing

• Nausea or vomiting

• An extra or skipped heartbeat (palpitations)

Diagnosis of a cardiac arrhythmia

Your child will be seen by a pediatric cardiologist. This is a doctor who treats heart problems in children. Your child may also be seen by a pediatric electrophysiologist. This is a doctor who is trained to treat electrical problems of the heart in children. The following tests may be done:

• Electrocardiogram (ECG). During this test, the electrical activity of the heart is recorded. It is checked for abnormal heart rhythms. Some problems of heart size or structure may be found as well. Small pads (electrodes) are placed on the chest, arms, and legs using stickers or tape. Wires connect the pads to an ECG machine. The machine records the heart’s electrical signals.

• Echocardiogram (echo). Sound waves (ultrasound) are used to create a picture of the heart and look for structural defects and problems with its pumping mechanism.

• Holter or event monitor. During these tests, the electrical activity of the heart is recorded for a longer period of time. This is done with a special device to track the heartbeat. A log is kept of your child’s activities and symptoms during the day. This log is then compared with the heart rhythm results. With a Holter monitor, the heartbeat is tracked for 24 hours or longer. With an event monitor, a button is pressed to record the heart rhythm each time your child has symptoms. It is used for longer periods, typically up to a month.

• Exercise stress test. During this test, the electrical activity of the heart is recorded while your child is exercising on a treadmill or a stationary bike. This is done to check how your child’s heart responds to different levels of activity (stress). Electrodes are placed on the chest, arms, and legs.

• Electrophysiology study (EP). This test measures the electrical activity of the heart. EP studies are done during a heart catheterization by a cardiologist with special training. Your child will need either sedation or general anesthesia. EP is a more invasive study. The heart is stimulated using catheters and special monitoring devices.

• Implanted loop recorder. This is a heart monitoring device that may be used when there is a concern for a high-risk arrhythmia and other testing has not had a clear result. This type of testing may only be used in children who are considered high risk. The device is implanted under the skin and is used for long-term monitoring.

Treating a cardiac arrhythmia

A minor arrhythmia may cause few symptoms. It may cause no problems in a child’s normal routine and growth. Your child may not need treatment. But an arrhythmia that causes severe or troublesome symptoms can lead to serious health problems if untreated. Treatment depends on the type of arrhythmia and may include:

• Medicines. These may be used to regulate your child’s heart rate.

• Catheter ablation. Thin, flexible tubes (catheters) with special wires are guided into the heart. The area(s) that are causing the arrhythmia are then destroyed with an electrical current or with cold. This breaks the electrical circuit causing the arrhythmia.

• Electrical cardioversion. An electric shock is given. This briefly stops the abnormal electrical action in the heart. It "resets" the heart's normal pacemaker. The heart can then restart in a normal rhythm.

• Pacemaker. This is a device that is placed in the chest with leads (wires) attached to the heart. It is placed in the abdomen if it’s for a newborn or infant. This device is used to create the electrical signal that makes the heart beat at a regular rate. A pacemaker may be used if the SA or AV node is not working properly. It may also be used if the ventricles aren't pumping as often as they should.

• Implantable cardioverter defibrillator (ICD). This is a device that is placed in the chest. It tracks the heart rate. It sends an electric shock to the heart to stop a dangerous fast heart rhythm if needed. This can be uncomfortable for the child when it fires, but it is a lifesaving measure.

Long-term concerns

A child with an arrhythmia can have an active life after treatment. The amount of activity will vary with each child. Check with the healthcare provider about what activities your child can do. Regular visits with a cardiologist may be needed for the rest of your child’s life. This is to make sure that the heart is working right. Your child may have a pacemaker or ICD. If so, the healthcare provider will need to check it regularly and replace the battery when it runs low.

All parents of children with an arrhythmia should learn what to do in an emergency. If your child collapses and is not responsive, call for help and tell someone to call 911. If there is an automated external defibrillator (AED), use it. Learn CPR so that you can support your child until emergency services arrive.