What Is an Implantable Cardioverter Defibrillator?
An implantable cardioverter defibrillator (ICD) is a
small device that's placed in your chest or abdomen. This device uses
electrical pulses or shocks to help control life-threatening, irregular
heartbeats, especially those that could lead the heart to suddenly stop beating
(sudden
cardiac arrest). If the heart stops beating, blood stops flowing to the
brain and other vital organs. This usually causes death if it's not treated in
minutes.
The Heart's Electrical System
Your heart has its own internal electrical system
that controls the speed and rhythm of your heartbeat. With each heartbeat, an
electrical signal spreads from the top of the heart to the bottom. As it
travels, the electrical signal causes the heart to contract and pump blood.
Electrical signals normally begin in a group of
cells called the sinus node. As these signals spread from the top to the bottom
of the heart, they coordinate the timing of heart cell activity. First, the two
upper chambers of the heart, called atria (AY-tree-uh), contract. This
contraction squeezes blood into the lower chambers of the heart, which are
called ventricles (VEN-trih-kuls). The ventricles then contract and send blood
to the rest of the body. The combined contraction of the atria and ventricles
is a heartbeat.
For more information about the heart's electrical
system and how a healthy heart works, see the Diseases and Conditions Index
article on
How
the Heart Works.
Overview
A problem with any part of the electrical system
process can cause irregular heartbeats called
arrhythmias
(ah-RITH-me-ahs). During an arrhythmia, the heart can beat too fast, too slow,
or with an irregular rhythm. Faulty electrical signaling in the heart causes
arrhythmias.
ICDs use electrical pulses or shocks to treat
life-threatening arrhythmias that occur in the ventricles (lower chambers of
the heart).
When these ventricular arrhythmias occur, the heart
can't effectively pump blood, and a person will pass out within seconds and die
within minutes if not treated. To prevent death, the condition must be treated
right away with an electric shock to the heart. This treatment is called
defibrillation.
An ICD has wires with electrodes on the ends that
connect to the chambers of your heart. The ICD will continually monitor your
heart rhythm. When the device detects that you're having an irregular rhythm in
your ventricles, the ICD will use low-energy electrical pulses to restore a
normal rhythm. If this doesn't restore your normal heart rhythm, or if your
ventricles start to quiver rather than contract strongly, the ICD will switch
to high-energy electrical pulses for defibrillation.
Doctors also treat irregular heartbeats with another
device called a pacemaker. An ICD is similar to a pacemaker, but there are some
differences. Pacemakers can only give off low-energy electrical pulses. They
are often used to treat less dangerous heart rhythms, such as those that occur
in the upper chambers of your heart. Most new ICDs can act as both pacemakers
and ICDs.
Comparison of an Implantable
Cardioverter Defibrillator and a Pacemaker
The illustration compares an
implantable cardioverter defibrillator and a pacemaker. Figure A shows the
location and general size of an implantable cardiac defibrillator in the upper
chest. The wires with electrodes on the ends are inserted into the heart
through a vein in the upper chest. Figure B shows the location and general size
of a double-electrode pacemaker in the upper chest. The wires with electrodes
on the ends are inserted into the heart through a vein in the upper chest.
For more information, see the Diseases and
Conditions Index article on
Pacemaker.
June 2007 |