About Your Procedure

About Implantable Cardioverter Defibrillators (ICDs)

You have been recommended to have an implantable cardioverter defibrillator (ICD) to treat your heart rhythm problem. The purpose of this guide is to help you and your family prepare for this procedure and for your recovery at home.

The Heart's Electrical System

Your heart is a muscle that works like a pump. The main job of your heart is to pump blood throughout your body. The heart is divided into a right and left side. Each side has an upper chamber, or atrium, that collects blood returning to the heart and a muscular lower chamber, or ventricle that pumps the blood away from the heart.

Medical illustration of a heart showing the left and right atria, which collect blood returning to the heart, and the left and right ventricles, which pump the blood away from the heart.

The pumping of your heart is regulated by an electrical current or impulse – much like a spark plug in a car. The electrical impulse starts in the sinoatrial (SA) node, often called the body’s natural pacemaker, and then spreads throughout both atria like ripples in a pond. This c auses both atria to contract squeezing blood into the ventricles.

The impulse then travels down to the atrioventricular (AV) node which is like a wire that connects it to the ventricles. The AV node splits into two branches, allowing the even spread of the electrical signal to both ventricles at the same time. This lets your heart beat effectively.


Medical illustration of a heart showing the sinoatrial node, the atrioventricular node, and the His-Purkinjie fibres, which control the electrical impulse that causes your heart to pump.

Heart Arrhythmias

Arrhythmias are an abnormality of the heart’s electrical system. Ventricular arrhythmias are rapid heartbeats in the lower chambers of the heart. This fast heart rhythm is either ventricular tachycardia (VT) or ventricular fibrillation (VF). Both of these arrhythmias can be life threatening because they prevent the heart from keeping the blood circulating throughout your body.

Implantable Cardioverter Defibrillators (ICDs)

Primary Prevention implantable cardioverter defibrillators (ICDs) are recommended for people who have not yet had a ventricular arrhythmia but who are at risk of having one.

Secondary Prevention ICD’s are recommended in people who have already experienced a ventricular arrhythmia and are at risk of having another one.

An ICD is a small device that is implanted under the skin and specially designed to monitor for heart rhythms that could be harmful. When the ICD picks up abnormal, rapid ventricular heart rhythms, it reacts by sending a series of rapid paced beats called anti-tachycardia pacing or by delivering an electric shock to the heart. Both of these actions are designed to quickly restore a normal heart beat. The ICD can also recognize if your heart is beating too slowly and send electric pacemaker signals to help your heart to beat at a normal rate.

Parts of an ICD

There are different ICD models, each of which works in slightly different ways. The decision about which ICD to implant is based on your particular situation.

The ICD has two basic parts: the ICD generator (often referred to as the battery) and one or more wires called leads. The ICD generator contains the battery, important wiring and computer components that make the ICD work properly. When the generator is implanted, it is programmed to recognize harmful heart rhythms. The leads are special wires that are connected on one end to the generator with the other end attached to a spot inside your heart.

Every year, thousands of people in Canada receive an ICD. Most people who have ICDs return to their normal active lives. For more information about life with an ICD, please ask us for the patient information CD titled “Implantable Defibrillator Therapy.” It provides extra information about living with ICD implants.

Illustration of a heart and an Implantable Cardioverter Defibrillator (ICD), showing the ICD generator and the electrical leads inserted into the heart.

In general, ICD’s are implanted on the left side of your chest just beneath your collar bone.

Depending on which ICD is implanted, expect to receive an information booklet form the company that made your device in the mail. This booklet will have extra information about your specific ICD.


How the ICD Works

When the generator senses abnormal heart rhythms, it sends out either pacing pulses called anti-tachycardia pacing or an electrical shock to the heart through the leads. The ICD does not prevent the abnormal rhythms from happening but it stops them as soon as they happen. The ICD will also store information about your heart’s electrical activity which is checked whenever you visit the Pacemaker/Defibrillator Clinic.

Anti-Tachycardia Pacing

When the ICD senses abnormally fast heart rhythms, it sends a series of tiny rapid electrical impulses that override the abnormal rhythm. This works to restore a normal heart beat. Usually you will not feel anything when this happens.


For abnormal heartbeats that are extremely fast, the ICD delivers an electrical shock to stop the arrhythmia. This shock is called defibrillation. It is delivered suddenly and the sensation lasts for a couple seconds. Some patients describe the feeling as a small thump in the chest while other s have felt a strong and uncomfortable sensation like being kicked in the chest.

Bradycardia Pacing

If your heart begins to beat too slowly, the ICD can act like a pacemaker and stimulate the heart to beat at a regular and healthy rate. Usually you will not feel anything when this happens.

Cardiac Resynchronization Therapy

A cardiac resynchronization (CRT) device is a specialized ICD designed for people with heart failure. It is designed to coordinate both sides of the heart to help it beat more efficiently. CRT devices are usually only used for people with certain types of heart failure.

Ensure that you know which type of ICD device you had implanted and write the name in the space provided at the beginning of this guide.