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Cardiac Defibrillators
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Smaller than the size of a palm, an ICD
packs a lot of power into a little space. It sends
electrical pulses to the heart when rhythms
get dangerously out of control, effectively
halting racing beats and protecting against
Sudden Cardiac Death.
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Almost everyone has seen
a physician on television,
paddles in hand, yelling
“Clear!”, then applying those paddles
to the chest of a patient to shock
him “back to life”. As dramatic as
the scene may be, defibrillation, or
shock, can be the only way to stop
certain deadly heart arrhythmias
before they kill.
For those who are at high risk of
the deadliest forms of arrhythmias –
ventricular tachycardia and ventricular
fibrillation – an internal “shocking”
device may provide the best defense
against sudden cardiac arrest. Such
a device, known as an implantable
cardioverter defibrillator (ICD), is
considered effective in fighting cardiac
arrest over 90 percent of the
time, an astounding success for a
condition that few survived as
recently as 15 years ago.
About ICDs
Implantable cardioverter defibrillators
(ICDs) are small devices, about the
size of a pager, that are placed below
the collarbone. Via wires, or leads,
these devices continuously monitor
the heart’s rhythm. If the heart beats
too quickly, the ventricles will not
have enough time to fill with blood
and will not effectively pump blood
to the rest of the body. Left unchecked,
the rapid heartbeat could cause death.
To intervene, the ICD issues a lifesaving
jolt of electricity to restore the
heart’s normal rhythm and prevent
sudden cardiac death.
ICDs also can act as pacemakers
when a heart beat that is too slow
(bradycardia) is detected.
Most ICDs keep a record of the
heart's activity when an abnormal
heart rhythm occurs. With this information,
the electrophysiologist, a
specialist in arrhythmias, can study
the heart's activity and ask about
other symptoms that may have
occurred. Sometimes the ICD can be
programmed to “pace” the heart to
restore its natural rhythm and avoid
the need for a shock from the ICD.
Pacing signals from the ICD are not
felt by the patient; shock signals are,
and have been described as a kick in
the chest.
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SUDDEN CARDIAC DEATH VS. HEART ATTACK
Cardiac arrest, or sudden cardiac death (SCD), happens when a heart rhythm
disturbance prevents the heart from operating properly and delivering blood
to the brain and other vital organs.
A heart attack occurs when a partial or complete vessel blockage interferes
with the ability of blood to flow to the heart, and heart muscle dies.
Cardiac arrest, or sudden cardiac death (SCD), is NOT a heart attack, but
a prior heart attack can put someone at risk for SCD.
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When is ICD therapy the right choice?
In the simplest terms, anyone who
has had or is at a high risk of having
ventricular tachycardia, fibrillation or
sudden cardiac arrest is a candidate
for an ICD.
Many people have both coronary
artery disease (the primary cause
of heart attacks) and an arrhythmia
(a heart rhythm disorder). They are
at particular risk for sudden cardiac
death and may be candidates for
ICDs, even though they have no
noticeable symptoms of an abnormal
heart rhythm.
A cardiac arrhythmia specialist should
evaluate cardiac patients if they have
experienced any of the following:
- A prior cardiac arrest
- Ventricular tachycardia (VT) which
is an episode of rapid heartbeat
originating from the lower chambers
of the heart
- Ventricular fibrillation (VF), which
is similar to VT but is characterized
by a heartbeat that is too rapid and
is irregular or chaotic
- Ejection fractions of less than 35
to 40 percent. An ejection fraction
(EF) is the proportion, or fraction,
of blood pumped by the heart with
each beat. A normal heart pumps
out a little more than half the
heart's volume of blood with each
beat, making a normal EF 55 percent
or higher
- Patients at a high risk for sudden
cardiac death (SCD) because of an
inherited heart abnormality
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MOST DANGEROUS RAPID HEART RHYTHM
Sudden rapid heartbeats originating in the ventricles are the most dangerous
arrhythmias. Ventricular tachycardia, a rapid yet steady beat is dangerous in
its own right. It can turn into ventricular fibrillation or VF, which is characterized
by irregular and chaotic rapid heartbeats. Because the fibrillating heart muscle
cannot contract and pump blood to the brain and vital organs, VF is the
number one cause of sudden cardiac death. Without immediate emergency
treatment of an electric shock to restore normal rhythm, an individual loses
consciousness within seconds and dies within minutes.
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