ICDs
An implantable cardioverter defibrillator (ICD) is a small implantable device
that looks similar to a pacemaker. Most ICDs can fit easily in the palm of your
hand. While pacemakers can speed up a slow heart rate, ICDs were designed to
slow down a fast heart rate. In addition, many ICDs also contain a built-in
full-featured pacemaker.
The ICD detects arrhythmias (both
bradyarrhythmia and
tachyarrhythmia) and delivers electrical therapy-pacing pulses or
defibrillation therapy as necessary. When not needed, the ICD merely monitors
the heart without delivering any electrical energy.
Often ICD therapy is prescribed for people who have experienced at least one
episode of ventricular
tachycardia or
ventricular fibrillation, previous cardiac arrest, or drug therapy that
was ineffective in controlling the
tachyarrhythmia or that caused severe side effects.
Though you may feel anxious about receiving an ICD, be assured that you are
joining hundreds of thousands of people who now enjoy more normal and active
lifestyles because of their ICDs.
The ICD system consists of three main components. Select a link below to jump
down the page:
ICD
The ICD consists of a mini-computer (the hybrid) powered by a battery, all
sealed in a titanium case. The battery is connected to a capacitor, which helps
the ICD to charge and store enough energy to deliver therapy when required.
To know if, when, and what type of therapy might be needed, the ICD monitors or
senses the heart. The ICD's computer brains can determine from certain patterns
of heart activity what type of arrhythmia is occurring. The ability to sort out
arrhythmias is called discrimination and it's done with very advanced software
formulas called algorithms. The algorithms make sure you get therapy when you
need it, while avoiding unnecessary therapy.
The ICD case is made of titanium, a metal that is 10 times as strong as steel,
but much lighter. In the United States, the National Aeronautics and Space
Administration (NASA) uses titanium to make rockets and satellites.
A typical ICD unit is small in size, often four to five ounces in weight, less
than two inches wide and a half-inch thin. This means that the device is
roughly the size of four to five silver dollars (United States currency)
stacked on top of one another.
ICD Lead
The ICD lead, which connects the ICD with the heart, is a flexible insulated
wire with an electrode tip. This tip, inserted into the heart through a blood
vessel, carries electrical impulses from the ICD to the heart. It also carries
information from the heart back to the ICD for access by a physician via a
programmer.
Today, most ICDs use transvenous leads, which are passed through the vein.
Previously, ICD systems most often used epicardial leads, which were sewn onto
the heart in an open-chest procedure. Nowadays, most ICDs are implanted without
open-chest surgery.
A defibrillator lead has a shocking coil near its tip to deliver defibrillation
therapy to the heart. All ICDs require at least one defibrillator lead, which
is placed in the right ventricle. A single-chamber ICD uses one pacing lead,
placed in or on the ventricle.
Sometimes ICDs are called single-chamber and dual-chamber. All ICDs from St.
Jude Medical defibrillate the ventricle only. The single- and dual-chamber
refers to the built-in pacemaker. A single-chamber ICD defibrillates the
ventricle and paces the ventricle. A dual-chamber ICD defibrillates the
ventricle and paces the atrium and ventricle.
Programmer
A special tabletop computer, a programmer, enables a physician to talk to the
pacemaker, even after it is implanted. The physician can evaluate the
pacemaker's performance and change settings noninvasively (without surgery). A
telemetry wand is placed on your chest over the implanted device, enabling the
pacemaker to communicate with the programmer and vice versa.
To facilitate programming, the programmer software provides high-speed
processing and easy operation. At the touch of a button, the unique Automated
Follow-Up feature delivers customized information on pacemaker function and
cardiac activity to help provide therapy specifically tailored to you.
Related Information
Select a link below to jump to another page:
Related Web Site
- Inside Cardiac Arrest
-
This site—created by St. Jude Medical—is an educational resource providing
information about sudden cardiac arrest and a review of the heart's anatomy.
Watch the “Am I at Risk?” video and commentary provided by Charles Machell, MD.
-
[ www.insidecardiacarrest.com
]
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