The heart is composed of four chambers enclosed within a wall of muscle. The upper two chambers (atria) will help fill the lower two chambers (ventricles) with blood. The ventricles are larger and more heavily muscled than the atria. They pump blood to the lungs and throughout the rest of the body.
The heart's natural pacemaker, located in the upper part of the heart, normally regulates your heart rate. This natural pacemaker, called the sino-atrial node (S-A node), is a small cluster of specialized cells that produce electrical signals at regular intervals. The S-A node automatically increases your heart rate in response to your body's needs - for example, during exercise, when a faster blood flow is required.
The electrical impulses sent out by the S-A node travel to the atrioventricular node (A-V node), a second cluster of cells located near the center of the heart. The A-V node then transmits the electrical signals out to the walls of the ventricles.
This natural electrical pathway is very important because when the signals reach the lower heart, both ventricles contract, pumping blood throughout the body. Sometimes things go wrong in the heart's electrical system. The heartbeat becomes irregular or changes its rate. This is called an arrhythmia. Dangerous arrhythmias may prevent the heart from pumping enough blood throughout the body, and your cardiologist may recommend implantation of an AICD.
Every AICD system has two parts; the pulse generator and the lead or leads. The pulse generator checks your heart's electrical signals and delivers electrical therapy when it senses a dangerous heart rhythm. The lead or leads connect the pulse generator to the heart. Based on settings programmed by your cardiologist, the AICD system watches your heart all the time. It waits for an arrhythmia to happen. If one is sensed, the AICD determines what type of electrical treatment, if any, you need. Then, it delivers the electrical treatment to return your heart rate to normal.
The AICD is usually implanted below the collarbone just beneath the skin. The leads are threaded into the heart through a vein located near the collarbone; the tip of each lead is then positioned inside the heart. However, sometimes the pulse generator is positioned in the abdomen and the pacemaker leads are attached to the outside of the heart. The decision, where and how to implant the pacemaker system, is made by your cardiologist based on individual needs.
Following implantation, your cardiologist will tell you when to call him and what to do if you experience an electrical treatment from your AICD. Periodic evaluations will be scheduled to monitor AICD function. During these visits your cardiologist will analyze your AICD using a programmer computer. Programmers are used to communicate with the AICD pulse generator for programming treatment and retrieving treatment history.