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Overview of Pacemakers and Implantable Cardioverter Defibrillators (ICDs) in Children


Overview of Pacemakers and Implantable Cardioverter Defibrillators (ICDs) in Children

What is an implanted pacemaker?

An implanted pacemaker is a small device implanted under the skin that sends electrical signals to control an irregular or slow heartbeat. An implanted pacemaker may be used to stimulate the heartbeat if the heart's natural pacemaker (the sinoatrial, or SA, node) is not working properly, has developed an abnormally slow rate, or if the electrical pathways are blocked.

Rhythm problems may occur in teens and young adults with congenital heart disease due to scar tissue buildup from prior surgeries and procedures.

Children's pacemakers may be placed under the skin in one of several locations. Young children (infants, toddler, preschool, and young school-aged children) often have the pacemaker generator placed in the abdomen, since the fatty tissue found there can help protect the generator from normal everyday childhood activities such as playing. As a child gets older (nearing adolescence), the generator is often placed in the shoulder area, just under the collarbone.

What is an implantable cardioverter defibrillator (ICD)?

An implantable cardioverter defibrillator (ICD) is a small device, similar to a pacemaker, that is implanted under the skin. An ICD senses the rate and regularity of the heartbeat. When the heart rate exceeds a rate programmed into the device, the ICD delivers a small, electrical pulse to the heart to slow the heart rate. Most newer ICDs can also function as a pacemaker by pacing the heart out of a rapid rhythm and taking over when the heart rate is dangerously low. When the heartbeat becomes so erratic and disorganized that the heart muscle cannot pump blood from the ventricles, an ICD can deliver a stronger electrical pulse — often referred to as a "shock" — that can restore organized electrical activity, and therefore an effective heartbeat, to the ventricles.

What is the reason for getting a pacemaker or an ICD?

The heart's natural pacemaker is the network of heart tissues that conduct the electrical impulse downward from the atria to the ventricles. When it malfunctions, the signals sent out may become erratic: either too slow, too fast, or too irregular to stimulate adequate contractions of the heart chambers. When the heartbeat becomes erratic, it is referred to as an arrhythmia (an abnormal rhythm of the heart, which can cause the heart to pump less effectively).

ICDs may be recommended for people with significant ventricular rhythm problems which could pose a risk for sudden death.

Arrhythmias can cause problems with contractions of the heart chambers by:

  • Not allowing the chambers to fill with an adequate amount of blood because the electrical signal is causing the heart to pump too fast.

  • Not allowing a sufficient amount of blood to be pumped out to the body because the electrical signal is causing the heart to pump too slowly or too irregularly.

Anatomy of the heart, view of the electrical system

How does the heart beat?

An electrical stimulus is generated by the sinus node (also called the sinoatrial node, or SA node), which is a small area of specialized tissue located in the right atrium (right upper chamber of the heart). The sinus node generates an electrical stimulus about 60 to 190 times per minute. The rate depends on the age of the child and his or her activity level. This electrical stimulus travels down through the conduction pathways, similar to the way electricity flows through power lines from the power plant to your house. This causes the heart's lower chambers to contract and pump out blood. The right and left atria (the two upper chambers of the heart) are stimulated first and contract a short time before the right and left ventricles (the two lower chambers of the heart).

The electrical impulse travels from the sinus node to the atrioventricular node (also called AV node), where impulses are slowed down for a very short period, then continue down the conduction pathway via the "bundle of His" into the ventricles. The bundle of His divides into right and left pathways to provide electrical stimulation to the right and left ventricles.

Normally, as the electrical impulse moves through the heart at rest, the heart contracts about 60 to 140 times a minute, depending on a person's age. Each contraction of the ventricles represents one heartbeat. The atria contract a fraction of a second before the ventricles so their blood empties into the ventricles before the ventricles contract

Under some abnormal conditions, certain heart tissue is capable of starting a heartbeat, or becoming the "pacemaker," just like the sinus node. An arrhythmia (abnormal heartbeat) may occur when:

  • The heart's natural pacemaker (the sinus node) develops an abnormal rate or rhythm.

  • The normal conduction pathway is interrupted.

  • Another part of the heart takes over inappropriately as pacemaker.

In any of these situations, the body may not receive enough blood because the heart can't pump out an adequate amount with each beat as a result of the arrhythmia's effects on the heart rate. The effects on the body are often the same, however, whether the heartbeat is too fast, too slow, or too irregular.

What are the components of a permanent pacemaker/ICD?

A permanent pacemaker has two components, including the following:

  • A pulse generator which has a sealed lithium battery and an electronic circuitry package. The pulse generator produces the electrical signals that make the heart beat. Many pulse generators also have the capability to interpret signals that are sent by the heart itself.

  • One or more wires (also called leads). Leads are insulated, flexible wires that conduct electrical signals to the heart from the pulse generator. The leads may also relay signals from the heart to the pulse generator. One end of the lead is attached to the pulse generator and the electrode end of the lead is positioned in the atrium (the upper chamber of the heart) or in the right ventricle (the lower chamber of the heart). In the case of a biventricular pacemaker, leads are placed in both ventricles.

Pacemakers can "sense" when the heart's natural rate falls below the rate that has been programmed into the pacemaker's circuitry.

Illustration of a single-chamber pacemaker

Pacemaker and ICD leads may be positioned in the atrium, ventricle, or both; or positioned to pace both ventricles, depending on the condition requiring the pacemaker to be inserted.

  • An atrial arrhythmia (an arrhythmia caused by a dysfunction of the sinus node or the development of an extra atrial pacemaker within the heart tissue that takes over the function of the sinus node) may be treated with a lead wire located in the atrium.

  • A ventricular arrhythmia, an interruption in the conduction pathways, or the development of another pacemaker within the tissues of the ventricle, may be treated with a ventricular pacemaker or ICD whose lead wire is located in the ventricle.

  • Commonly, pacemakers and ICDs have lead wires positioned in both the atrium and the ventricle. There may be one lead wire for each chamber, or one lead wire may be capable of sensing and pacing both chambers.

  • Pacemakers that pace either the right atrium or the right ventricle (but not both) are called "single-chamber" pacemakers. Pacemakers that pace both the right atrium and right ventricle of the heart and require two pacing leads are called "dual-chamber" pacemakers.

  • An ICD always has a lead wire that is positioned in the ventricle ("single-chamber"), as it is used for treating fast ventricular arrhythmias. ICDs can also be "dual-chamber", meaning they have a lead wire positioned in the right atrium as well as the ventricle.

  • Some pacemakers and ICDs can provide cardiac resynchronization therapy (CRT) using three leads: one in the right atrium, one in the right ventricle, and one in the left ventricle. These CRT devices are used only in specific situations.

How is a pacemaker/ICD implanted?

Pacemaker/ICD insertion is done in the hospital, either as a short-stay surgical procedure, or in the cardiac catheterization or electrophysiology lab. The child may be awake during the procedure, although local anesthesia is given over the incision site, and generally sedation is given to help the child relax during the procedure.

In older children and teenagers who receive a transvenous pacemaker, a small incision is made just under the collarbone. The pacemaker/ICD lead(s) is inserted into the heart through a blood vessel which runs under the collarbone. This procedure is usually done in the catheterization lab.

X-ray of a single-chamber implanted pacemaker

The picture above is a chest X-ray. The large, white space in the middle is the heart. The dark spaces on either side are the lungs. The small object in the upper corner is an implanted pacemaker.

In younger children, the pacemaker may be placed into the abdomen through a small incision, with the leads placed directly on the surface of the heart. This procedure is usually done in the operating room. Once the procedure has been completed, the child goes through a recovery period of several hours and often is allowed to go home the day after the procedure.

After receiving a pacemaker or ICD, you will receive an identification card from the manufacturer that includes information about your child's specific model of pacemaker and the serial number as well as how the device works. You should carry this card with you at all times so that the information is always available to any health care professional who may have reason to examine and/or treat your child. Your child can also wear a medical identification bracelet or necklace  to alert others about the pacemaker or ICD in case of emergency.