To understand abnormal heart rhythms, or heartbeats, it can be helpful to first understand how your heart’s electrical system governs the heartbeat.
The Heart's Electrical System
Over the course of your life so far, you were most likely familiar with the heart because of its beating. Perhaps you heard your heartbeat through a stethoscope or listened to someone else's heartbeat. Or maybe you put two fingers to your wrist or neck to feel your pulse. Your pulse is your heartbeat sensed in your arteries.
Your heartbeat is the relaxing and contracting of your heart's chambers: the atria and ventricles. This process is stimulated by electrical impulses that travel through your heart and regulate your heartbeat. The electrical impulse begins in the sinoatrial (SA) node in the top of the right atrium and travels through the muscles of both atria. The atria contract in response. The electrical impulse is then picked up by the atrioventricular (AV) node, which is between the atria and the ventricles, and passed to the fibers of the His-Purkinje system. The ventricles fill with blood from the atria before the electrical impulse causes them to contract. Once the ventricles do contract, they force the blood out of the heart and to the lungs and body.
The timing of the flow of blood through the heart is key for good health. Problems with the heart's electrical system can be life threatening. A patient's care team may advise implantation of a pacemaker or other treatment.
Abnormal Heart Rhythms
An abnormal heart rhythm – or heartbeat – is called an arrhythmia or dysrhythmia. The number of heartbeats in a minute determines the heart rate. Normal heart rates change as a child matures. The heart of a newborn baby normally beats about 140 times per minute. A five-year-old may have a heart rate of 100 beats a minute. And the normal heart rate of an older child or teenager at rest is about 70 beats a minute. The heart rate changes easily. During exercise, it beats faster. During rest, it slows.
Usually the heart beats at regular intervals. Arrhythmia, or dysrhythmia, occurs when it beats irregularly. One type of arrhythmia – sinus arrhythmia – is normal. It occurs when a child breathes in and the heartbeat increases and when he or she breathes out and the heart rate slows.
If your child’s doctor detects another kind of arrhythmia, he or she may recommend tests and/or a visit to a pediatric cardiologist (a doctor with special medical training in children's heart problems).
Often an irregular heartbeat has no symptoms and goes unnoticed by parents and the child. Sometimes, it is detected during a routine wellness exam. Medications – those that are prescribed and those bought without prescription at your pharmacy – may contribute to your child’s irregular heartbeat. Talk with your doctor about your child’s medications if an irregular heartbeat is detected.
Kinds of Abnormal Heart Rhythms
Some abnormal heart rhythms are fast, others are slow and some are irregular. How an arrhythmia is treated depends on the kind of abnormal beat. Read more about arrhythmias that most commonly develop in children and young adults:
- Fast heart rhythms
- Slow heart rhythms
- Irregular heart rhythms
Fast Heart Rhythms (Tachycardia)
Supraventricular Tachycardia (SVT)
In this abnormal heart rhythm, the impulse stimulating the heart does not come from the sinus node. Instead, it comes from a collection of tissue involving the atrioventricular (AV) node. Electrical impulses are generated at a rapid rate, which may result in 280 heart beats per minute. Treatment is possible with the Valsalva Maneuver, in which the patient is asked to strain, or bear down, in order to slow the heart rate. If this is not effective, medications can be used to slow the heart rate. For those with severe SVT, cardioversion may be recommended. In cardioversion, an electrical shock is delivered to the heart to change an abnormal heart rhythm back to a normal rhythm.
Atrial Flutter
This condition occurs when rapidly fired signals cause the muscles in the atria to contract quickly, leading to a very fast and steady heartbeat. Treatment is possible through the use of medications. Those with severe atrial flutter may be treated with cardioversion, an electrical shock delivered to a rapidly beating heart to return it to a normal rhythm.
Ventricular Tachycardia
This is a dangerous type of rapid heart rhythm usually associated with poor cardiac output (amount of blood ejected from the heart). It arises in the heart’s lower chambers (ventricles) from tissues that generate a rapid and irregular heart rhythm. Ventricular tachycardia is a life-threatening emergency that may require electrical shock therapy (cardioversion).
Slow Heart Rhythms (Bradycardia)
Atrioventricular Block (AVB)
AV block occurs when some or all of the electrical signals traveling from the heart's upper chambers (atria) to the lower chambers (ventricles) are impaired or fail to transmit. This is "heart block" or "AV (atrioventricular) block." In this condition, the atria (upper chambers) may contract at a normal rate, but the signals to the ventricles are “blocked.” There are various types of AV block depending upon the mechanism of block. For example, second degree AV block occurs when the electrical impulse from the atria is blocked every certain number of beats. In “complete AV block,” none of the signals pass through the atrioventricular node, leaving the ventricles to generate their own rhythm. A pacemaker, a small implanted device that stimulates the heart to beat at a certain rate, is a recommended treatment for AV block.
Irregular Heart Rhythms
Premature Atrial Contraction (PAC)
In this condition, an impulse generated in the upper chambers “fires” early. This causes the heart to beat earlier than normal, resulting in an irregular heart rhythm. PAC typically does not require therapy. However, if it is severe, medications may be prescribed to control it.
Premature Ventricular Contraction (PVC)
In PVC, the ventricles (lower heart chambers) generate an early impulse which causes the heart to beat earlier than normal, resulting in irregularity in the heart rhythm. It typically does not require therapy, particularly if it occurs infrequently. More frequent PVCs require treatment with medications. The cause of PVC should be investigated as it may reflect heart muscle disease.
Atrial Fibrillation (AF)
In AF, which is unusual in children, many sites within the heart’s upper chambers generate irregular electrical impulses to cause an irregular heart beat. Electrical shock therapy (cardioversion), in which the heart is “shocked” back into normal rhythm, and medications are used to treat AF.