Overview of Pacemakers and Implantable Cardioverter Defibrillators (ICDs)
What is a permanent pacemaker?
A permanent pacemaker is a small device implanted in the chest to send electrical
signals to start or regulate a slow heartbeat. It's most often placed in the chest
area just under the collarbone. A pacemaker may be used if the heart's natural pacemaker
(the SA node) is not working properly causing a slow heart rate or rhythm, or if the
electrical pathways are blocked.
Another specialized type of pacemaker, called a biventricular pacemaker, is used for
ventricles that don't contract at the same time. This can worsen heart failure. A
biventricular pacemaker paces both ventricles at the same time, increasing the amount
of blood pumped by the heart. This type of treatment is called cardiac resynchronization
What is an implantable converter defibrillator (ICD)?
An implantable cardioverter defibrillator (ICD) looks similar to a pacemaker, though
slightly larger. It works very much like a pacemaker. However, the ICD can send a
low-energy shock that resets an abnormal heartbeat back to a normal. It can also send
a high-energy shock if an arrhythmia becomes so severe that the heart can't pump at
Many devices combine a pacemaker and ICD in one unit for people who need both functions.
After the shock is delivered, a "back-up" pacing mode is available if needed for a
The ICD has another type of treatment for certain fast rhythms called anti-tachycardia
pacing (ATP). This is a fast-pacing impulse sent to correct the rhythm. This can be
used instead of shocking the heart in some cases.
What is the reason for getting a pacemaker or an ICD?
Pacemakers are most often used when your heart beats too slowly. ICDs are advised
if you are at risk for potentially fatal ventricular arrhythmias. There may be other
reasons for your healthcare provider to advise placement of a pacemaker or ICD.
When your heart's natural pacemaker or electrical circuit malfunctions, the signals sent
out may become erratic: either too slow, too fast, or too irregular (arrhythmia).
Arrhythmias can cause problems with contractions of the heart chambers by:
Not allowing your heart chambers to fill with enough blood because the heart pumps
Not allowing enough blood to be pumped out to your body because your heart pumps too
slowly or too irregularly.
How does the heart beat?
The heart is, in the simplest terms, a pump made up of muscle tissue. The heart's
pumping action is regulated by an electrical conduction system that coordinates the
contraction of the filling and pumping chambers of the heart.
In an adult, the sinus node generates a steady electrical stimulus. The right and
left atria (the two upper chambers of the heart) are stimulated first and contract
a short period of time before the right and left ventricles (the two lower chambers
of the heart). The electrical impulse travels from the sinus node through the atria
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,
called bundle branches, to provide electrical stimulation to the right and left ventricles.
At rest, the heart normally contracts about 60 to 100 times a minute, depending on
your age and physical condition. Each contraction of the ventricles is 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. An arrhythmia (abnormal heartbeat) occurs when:
The heart's natural pacemaker develops an abnormal rate or rhythm
The normal conduction pathway is interrupted
Another part of the heart takes over as pacemaker
In any of these situations, the body may not get enough blood because the heart cannot
pump well. The effects on your body are often the same, however, whether the heartbeat
is too fast, too slow, or too irregular. Some symptoms of arrhythmias include:
Low blood pressure
Shortness of breath
The symptoms of arrhythmias may look like other medical conditions. See your healthcare
provider for a diagnosis.
What are the components of a permanent pacemaker/ICD?
A permanent pacemaker or ICD has 3 main components:
A pulse generator with a sealed lithium battery. The pulse generator produces the
electrical signals that make the heart beat. Most pulse generators can also receive
and respond to signals that are sent by the heart itself.
One or more wires (also called leads). Leads are insulated flexible wires that conduct
electrical signals between the heart and 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 heart. In the case of a biventricular pacemaker, leads are placed on both
Electrodes, which are found on each lead.
Pacemakers can "sense" when the heart's natural rate falls below the rate that has
been programmed into the pacemaker.
Pacemakers that pace either the right atrium or the right ventricle 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. Pacemakers
that pace the right atrium and right and left ventricles are called "biventricular"
How is a pacemaker/ICD implanted?
Your doctor will insert the pacemaker or ICD in the cardiac catheterization, or the
electrophysiology lab. You are awake during the procedure, although your doctor will
provide local anesthesia over the incision site. He or she will also sedate you to
help you relax during the procedure. You may need to spend the night in the hospital
so that your doctor can make sure the device is working properly.
Shown here 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 right corner
is an implanted pacemaker.
Your doctor will make a small incision just under the collarbone (clavicle). He or
she will insert the pacemaker/ICD lead(s) into the heart through a blood vessel that
runs under the collarbone. Once the lead is in place, your doctor can test it to make
sure it is in the right place and is working. He or she then attaches the lead to
the generator (battery), which is placed just under the skin through the incision
made earlier. Your doctor will close the incision with stitches, stapes, or a medical
adhesive (glue) and apply a dressing. Once the procedure has been completed, you will
go through a recovery period or several hours.
There are certain instructions related to having an implanted permanent pacemaker
or ICD. For example, after you get your pacemaker or ICD, you will get an ID card
from the manufacturer that includes information about your 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 healthcare
professional who may have reason to examine or treat you.
After you have a pacemaker or an ICD implanted make sure you ask and understand the
instructions from your healthcare provider regarding:
Medicines you should be taking
Any precautions that should be observed with your device
How often you should have follow up appointments
How your device will be monitored
Signs and symptoms you should report to your healthcare provider after the procedure