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.