IN THIS ISSUE

Learning Center

What's Inside of Me?

Pacemakers. Leads. ICDs. CRTs. It can be hard to understand the difference. Here are some simple explanations for devices.

What is the difference between a pacemaker and an ICD?

Both a pacemaker and an ICD (implantable cardioverter defibrillator" are devices implanted in the chest to deliver electrical impulses to the heart. A pacemaker is used when the heart beats too slowly. An ICD is used when the heart beats too quickly in an abnormal, potentially life-threatening rhythm.

Impulses in a pacemaker increase the heart rate to a more normal rate. These impulses are tiny and most people cannot feel them. Pacemakers send out these impulses often to help even out the rhythm. A pacemaker is about the size of a matchbook.

Electrical impulses from an ICD slow down the heart rate by converting an abnormally fast rhythm to a more normal rhythm. The impulses from an ICD can be intense and may feel like a kick in the chest. But it is good to know that the ICD is treating the problem. ICDs activate as needed and most are about the size of a jelly jar lid.

ICDs are a combination of an ICD and a pacemaker.

What device is used for heart failure?

In a healthy heart, both ventricles (lower part of the heart) pump or beat at exactly the same time in a coordinated way. It’s like making a fist—all of the fingers squeeze in unison. But for many people with heart failure, the ventricles do not pump at the same time. For these people, the pumping is uncoordinated. It’s like making a fist just one finger at a time.

Cardiac Resynchronization Therapy (CRT) helps restore proper coordination so that your heart pumps more efficiently.

A CRT system consists of several components—the pulse generator and three thin, insulated wires called leads. A CRT device delivers electrical impulses to the heart through these leads. This helps restore the normal timing of the heartbeats, causing both ventricles to pump together again. CRT helps both sides of your heart work together. It’s like a fist closing normally again.

There are two types of CRT devices. One is a special kind of pacemaker. It’s called a cardiac resynchronization therapy pacemaker (CRT-P) or biventricular pacemaker. The other is the same device, but it also includes a built-in ICD. This type is called a cardiac resynchronization therapy defibrillator (CRT-D).

What is a pulse generator?

A pulse generator is part of a pacemaker or defibrillator system. The pulse generator is the power source for the system. It is also the "brain" of the device. The doctor programs the pulse generator to monitor a specific heart problem.

The pulse generator monitors the heart. It determines if the heart is beating too quickly or too slowly, depending on how the doctor has programmed it. Then, when needed, it sends an electrical impulse to the heart through the leads to speed up or slow down the heart.

What is a lead? (pronounced “leed”)

Learn More

Heart and Blood Vessel Basics

Cardiovascular Disease: Blood Vessel and Heart Problems

Talk to your doctor about important safety information.