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ICD vs. Pacemaker: What’s the Difference?

Heart and pacemaker

Implantable cardioverter defibrillators (ICD) and pacemakers are both medical devices that treat irregular heart rhythms, known as arrhythmias. These devices are surgically placed inside the body and help make sure the heart beats at a steady pace that meets an individual’s needs. They each work in different ways, which are important to discern because understanding how these devices work and what they can do for you can help you make decisions and anticipate life with your new device.

Keeping the Beat: The Body’s Natural Pacemaker

Our hearts each have their own internal pacemaker called the sinoatrial (SA) node or sinus node. The SA node is a collection of cells in the top of the right corner of the heart that naturally makes electrical impulses. These pulses start every heartbeat by traveling down a specific path within the heart to reach the ventricles. If this path is disrupted for any number of reasons, a heart may beat too fast, too slow, too weakly, or too irregularly. These problematic heartbeats are called arrhythmias.

Various heart problems can disrupt your heart’s electrical pathways so electrical impulses cannot pass properly through the heart, leading to arrhythmias. See a few below:

  • damage to the heart from heart disease or heart attack
  • heart surgery complications
  • longstanding, uncontrolled high blood pressure or coronary artery disease
  • a lack of coronary artery blood flow, depriving oxygen to heart tissue
  • cardiomyopathy distorting the heart’s structure
  • sarcoidosis
  • metabolic problems, such as hypothyroidism
  • side effects of certain medications
  • illicit and street drugs, such as cocaine

What is an Artificial Pacemaker?

An artificial pacemaker is a battery-powered medical device that emits electrical pulses to the heart to help it beat when the SA node, or some other part of the heart, is not working effectively and keeping the heart from beating correctly. Pacemakers stimulate the heart’s muscles and regulate its contractions to keep blood pumping through the body. When set correctly, a pacemaker helps regulate an individual’s heart rate, both while they are at rest and when they are active.

How Do Artificial Pacemakers Work?

An artificial pacemaker is made up of two main parts, the generator and the leads. The generator is the battery pack of the pacemaker and is usually inserted into the wearer’s chest and buried beneath the skin. The generator is attached to leads, which are tiny wires that connect to the wearer’s heart. The pacemaker’s generator makes impulses that the leads carry to the heart. These pulses are timed regular intervals that mirror how a healthy SA node would beat.

Most pacemakers used today can sense the person’s heart rate to help inhibit the pacemaker from sending impulses when the heartbeat does not need it. Artificial pacemakers can be used to treat the following heart rhythm problems:

  • A heartbeat that is too slow and irregular.
  • A heartbeat that is sometimes normal and sometimes too fast or too slow.

Types of Pacemakers

Internal artificial pacemakers are inserted through surgery. They are often used when treating:

  • Patients who have had a heart attack and their heart sustained enough damage to need help keeping the right pace.
  • Patients who have heart defects (either present at birth or developed later in life) that cause chronic slow or irregular heartbeats

Patients who are experiencing heart failure. External pacemakers are not surgically implanted. These temporary devices can never replace a permanent pacemaker pacing. However, they do help patients who are either waiting for a permanent pacemaker, or only experiencing a temporary arrhythmia due to other health conditions. External pacemakers are often used for treating:

  • Some patients who have had a heart attack
  • Patients with chest or cardiac trauma
  • Infections (Lyme disease or bacterial endocarditis), sepsis, etc.

Patients with a slow heart rate caused by electrolyte disturbances, metabolic abnormalities, medications (such as beta-blockers), or hypothermia.

Leadless pacemakers are a single unit in the shape of a capsule that is attached directly onto the left ventricle of the heart. They are 90% smaller than a standard implantable pacemaker. Leadless pacemakers have fewer risks than standard implantable pacemakers. They also don’t show under your skin, or result in a scar from the surgery to place them. However, only one leadless pacemaker model is currently FDA approved for use, with others on the way. So, leadless pacemakers are a newer technology that is more difficult to access.


Artificial pacemakers have been used to treat arrhythmias for decades. However, some risks still remain, including device malfunction, infection near the implantation site, and blood clots. But thanks to years of advancements made in artificial pacemaker research and care, people with pacemakers can live long, fulfilling, and active lives.

Learn more about living with a pacemaker from the American Heart Association.

What is an ICD?

An implantable cardioverter-defibrillator (ICD) is a device used in patients who are at high risk for life-threatening cardiac arrest or ventricular arrhythmias. This battery-powered device tracks an individual’s heart rate and delivers an electric shock, not unlike the shock that automated external defibrillators deliver, only ICDs do it from the inside whenever they detect dangerous irregular activity. They do not need someone operating them for the patient, they function on their own.

How Do ICDs Work?

Some ICDs in use today also function as an artificial pacemaker for the person wearing the device, which means they will also measure the person’s heart rate and send small pulses to keep it regular on an ongoing basis.

The larger shocks ICDs deliver are intended to restore a normal heart rate and rhythm when the heart falls too far out of beat for regular artificial pacemaker pulses. ICDs are deemed necessary when the arrhythmia present is considered more immediately life-threatening or not fixable with surgery. ICDs are programmed to address specific heart problems, which means they can deliver varying levels of energy when the shock is provided depending on what is needed. This includes:

  • Low-energy pacing. When your ICD responds to mild changes in your heartbeat, it will deliver low-energy pacing, which may not feel like anything or may feel like a small, painless fluttering in your chest.
  • A higher energy shock. For more serious arrhythmias, the ICD delivers a higher energy shock to regulate the heart, which can be painful. Some wearers of the device have noted that it can feel as if you’ve been kicked in the chest. The pain usually lasts only a second, and there shouldn’t be discomfort after the shock ends.

Newer models can also track your heart rate over a period of time, which can help your doctor gain important insights, such as:

  • How well your medications are working
  • Whether any adjustments need to be made to the ICDs programming

The following situations may render a recommendation for an ICD:

Types of ICDs

According to Mayo Clinic, there are two basic types of ICDs that are implanted:

  • Traditional ICD — implanted in the chest, and the wires (leads) attach to the heart. The implant procedure requires invasive surgery.
  • Subcutaneous ICD (S-ICD) — implanted under the skin at the side of the chest below the armpit. It’s attached to an electrode that runs along the breastbone. An S-ICD is larger than a traditional ICD but doesn’t attach to the heart.


Higher energy shocks for more serious heart rhythm problems may be more painful than lower energy shocks, but pain typically only lasts briefly and is a sign that the device is doing its job—-keeping a heart beating! Other than sometimes being a bit painful and startling, ICDs have similar risks as artificial pacemakers, including device malfunction, infection near the implantation site, and blood vessel damage from the leads.

While living with an ICD can be daunting, especially if you have to make the decision quickly due to experiencing Sudden Cardiac Arrest, recent research shows that ICDs can improve your quality of life and even extend your life.

Learn more about living with an ICD from the American Heart Association.

ICD vs. Pacemaker: Similarities & Differences

ICDs and pacemakers are both internally implanted medical devices used to treat various types of arrhythmia. Pacemakers deliver low-energy electrical pulses that help make sure the heart beats at a steady pace to meet an individual’s needs. ICDs are slightly larger than pacemakers and also monitor the heart for abnormal beating, but they can also deliver a shock if a dangerous rhythm is detected.

Implantation Procedures

Getting a pacemaker or an ICD will require surgery. For any of these procedures, you may be lightly or heavily sedated or even put under general anesthesia. You will likely spend the night at the hospital afterward so your care team can program your new device and watch to make sure it works. You will also need to arrange to have someone else drive you home from the hospital.

Your doctor will also talk to you about what activities you can and cannot do after surgery. They will also help you understand how best to manage your new device throughout your life.

Pacemaker Implantation

According to Mayo Clinic, surgeons implanting an artificial pacemaker will insert one or more wires (leads) into a major vein under or near the collarbone and guide them to the heart. One end of each wire is secured at the correct position in the heart, and the other end is attached to the pulse generator, which is usually implanted under the skin beneath the collarbone.

The procedure for placing a leadless pacemaker is less invasive, since the surgeon only has to place the one unit. The procedure involves the surgeon entering through a vein in the groin and then guiding the capsule through to the proper position in the heart.

External pacemakers do not require surgery.

ICD Implantation

The procedure to implant an ICD usually takes a few hours and is very similar to the procedure to implant a pacemaker. The doctors will place the leads that connect to the generator of the device on your heart and then place the generator beneath your collar bone.

After placing the ICD, your care team will have to test it to make sure it works. They will also program it to fit your specific heart rhythm needs. This process may require that your care team speeds up your heart and then shocks it back into a regular rhythm.

Maintenance and Battery Life Expectancies

Pacemakers and ICDs can send information about how they are functioning to doctors wirelessly or even over a telephone line. Your care team will want to check your device periodically to ensure it is still working and no changes need to be made. They can do this in person, over the phone, or digitally depending on the type of pacemaker or ICD you have. They will want to check in with you regularly to find out how the device you have is working, how the battery is doing, and how your condition is developing.

A pacemaker’s battery will last anywhere from 5 to 15 years. Meanwhile, ICDs use a lithium battery that can last anywhere from 5 to 7 years. Minor surgery is required to replace batteries for both devices.


Certain electronics, magnets, and other common devices can interfere with a pacemaker or ICD. This can be dangerous to your health. Luckily, the American Heart Association has a helpful list of Devices that May Interfere with ICDs and Pacemakers.


It can be scary and stressful for patients to live with known underlying heart conditions. Implanted cardiac therapy devices like ICDs and pacemakers can provide protection and treatment,These devices are often used alongside other therapies, such as certain medications or corrective heart procedures. These devices have come a long way since their inception many years ago, and scientists are making advancements in the technology behind ICDs and artificial pacemakers all the time. When included as a part of a patient’s care plan, these devices can allow a person with a known heart condition to experience a greater quality of life and extend their life.

In this video, Austin McAnena, President of Heartshield Project and a 2X SCA survivor, spoke to Avive about his recovery after SCA and living with an ICD.

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