Implantable Cardiac Defibrillators
What are implantable cardiac defibrillators?
An implantable cardiac defibrillator (ICD) is a small
electronic device installed inside the chest to prevent
sudden death from cardiac arrest due to life threatening
abnormally fast heart rhythms (tachycardias). The ICD is
capable of monitoring the heart rhythm. When the heart is
beating normally, the device remains inactive. If the heart
develops a life-threatening tachycardia, the ICD delivers
an electrical "shock(s)" to the heart to terminate the
abnormal rhythm and return the heart rhythm to normal.
How does a normal heart function?
The heart is an organ consisting of four chambers that pump
blood. The two upper chambers are called the right and left atria, and the two
lower chambers called the right and left ventricles. The right atrium receives
venous blood (oxygen-poor blood) from the body and pumps it into the right
ventricle. The right ventricle pumps the oxygen-poor blood to the lungs to
receive oxygen. The oxygen-rich blood from the lungs then travels to the left
atrium and is pumped by the left atrium into the left ventricle. The left
ventricle delivers the oxygen-rich blood to the rest of the body. In addition to
oxygen, the blood carries other nutrients (glucose, electrolytes, etc.) to the organs.
In order to keep a body healthy, the heart must deliver a sufficient amount of blood to the
body. As a pump, the heart is most efficient in delivering blood when
functioning within a certain heart rate range. Normally, the heart's natural
pacemaker called the SA node (a special
tissue located on the right atria wall), keeps the
heartbeat (heart rate) in the normal range. Electrical
signals generated by the SA node travel along special
conduction tissues on the walls of the atria and the
ventricles. These electrical signals cause the heart
muscles to contract and pump blood in an orderly and
efficient manner.
How do abnormal heart rhythms
decrease blood delivery by the heart?
Abnormal heart rhythms, either too slow or too fast,
decrease the delivery of blood by the heart. Bradycardia
is a condition in which the heart rate is too slow.
Bradycardias can be due to diseases of the SA node or the
conduction tissues of the heart. The slow-beating heart
delivers an insufficient amount of blood to the body.
Please see the Pacemaker
article of MedicineNet.com for information regarding
the causes and treatment of bradycardias.
Tachycardia is a condition in which the heart rate is
too rapid. When the heart pumps too fast, the ventricles do
not have enough time to fill their chambers with blood
before the next contraction. Therefore, tachycardias can
decrease the amount of blood delivered to he body. One of
the effects of decreased blood delivery to the body is low
blood pressure.
Next: What is the cause of tachycardias? »
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From the Doctors at MedicineNet.com  |
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- Low Blood Pressure - Learn about low blood pressure (hypotension). Low blood pressure is blood pressure below normal and symptoms may include: lightheadedness, dizziness, fainting upon standing (orthostatic hypotension). There are many causes of low blood pressure, and treatment is dependant upon the cause. Source:MedicineNet
- Heart Attack - Overview on heart attack (myocardial infarction) and heart attack symptoms including signs of a heart attack, includes causes, risk factors, prevention, and treatment. Produced by medical doctors. Source:MedicineNet
- Pacemaker - Learn about the pacemaker - an electronic device used to treat patients with abnormally slow or irregular heartbeats on MedicineNet.com Source:MedicineNet
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