What Is an Implantable Cardioverter Defibrillator?
An implantable cardioverter defibrillator (ICD) is a
small device that's placed in your chest or abdomen. The device uses electrical
pulses or shocks to help control life-threatening, irregular heartbeats,
especially those that could cause
sudden
cardiac arrest (SCA).
SCA is a condition in which the heart suddenly and
unexpectedly stops beating. 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.
Understanding the Heart's Electrical System
Your heart has its own internal electrical system
that controls the rate and rhythm of your heartbeat. With each heartbeat, an
electrical signal spreads from the top of your heart to the bottom. As the
signal travels, it causes the heart to contract and pump blood.
Each electrical signal normally begins in a group of
cells called the sinus node or sinoatrial (SA) node. As a signal spreads from
the top of the heart to the bottom, it coordinates the timing of heart cell
activity.
First, the hearts two upper chambers, the
atria (AY-tree-uh), contract. This contraction pumps blood into the
hearts two lower chambers, the ventricles (VEN-trih-kuls). The ventricles
then contract and pump blood to the rest of the body. The combined contraction
of the atria and ventricles is a heartbeat.
For more information on the hearts electrical
system and detailed animations, go to the Diseases and Conditions Index
How
the Heart Works article.
Overview
A problem with any part of the hearts
electrical system 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 (the hearts
lower chambers).
When ventricular arrhythmias occur, the heart can't
effectively pump blood. You can 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
(de-fib-ri-LA-shun).
An ICD has wires with electrodes on the ends that
connect to your heart chambers. The ICD will continually monitor your heart
rhythm. If the device detects an irregular rhythm in your ventricles, it will
use low-energy electrical pulses to restore a normal rhythm.
If the low-energy pulses dont 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. These pulses last only a fraction of a second, but they can be
painful.
Doctors also treat arrhythmias 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. Theyre 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 defibrillators.
Comparison of an Implantable
Cardioverter Defibrillator and a Pacemaker
![The illustration compares an ICD and a pacemaker. Figure A shows the location and general size of an ICD 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 pacemaker in the upper chest. The wires with electrodes on the ends are inserted into the heart through a vein in the upper chest.](https://webarchive.library.unt.edu/eot2008/20090825100456im_/http://www.nhlbi.nih.gov/health/dci/images/icd.jpg)
The illustration compares an ICD and
a pacemaker. Figure A shows the location and general size of an ICD 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 pacemaker in the upper chest. The wires with electrodes on the ends are
inserted into the heart through a vein in the upper chest.
Patients who have
heart
failure may need a special device called a cardiac resynchronization
therapy (CRT) device. The CRT device is able to pace both ventricles at the
same time. This allows them to work together and do a better job pumping blood
out of the heart. CRT devices that have a defibrillator are called
CRT-D.
Revised August 2009 |