Do you know the difference between a pacemaker and an implantable defibrillator?

by Carolyn Thomas  ♥  @HeartSisters

Before surviving a heart attack, I knew virtually nothing about pacemakers (they were just something that old people have to get, right?) and absolutely nothing about the cardiac device called implantable cardioverter defibrillators, or ICDs. 

In fact, the first time I laid eyes on a person with an ICD was at my 7-week Heart To Heart cardiac support group after I was discharged from hospital. 

One of the people in my group was a lovely, athletic 24-year old woman who had been diagnosed with a rare and serious heart arrhythmia called Long QT Syndrome.* Her sister had recently died suddenly due to the same condition.

This young woman was accompanied every week to our meetings by her mother. I could only imagine the impact of this catastrophic diagnosis on the mother, who had already buried one daughter because of it, and was now living with the knowledge that her surviving daughter carried the same deadly (and largely invisible) diagnosis. Her daughter’s ICD device was about the size of a small cellphone, its corners easily visible beneath the taut skin of her upper chest.

Both ICDs and pacemakers are medical devices that are implanted inside the bodies of heart patients. But what’s the difference between the two? Here’s some useful info, courtesy of the American College of Cardiology:

“A pacemaker is a small device that’s placed under the skin of your chest or abdomen to help control abnormal heart rhythms. This device uses electrical pulses to prompt the heart to beat at a normal rate. Pacemakers are used to treat heart rhythms that are too slow, fast, or irregular. These abnormal heart rhythms are called arrhythmias. Pacemakers can relieve some symptoms related to arrhythmias, such as fatigue or fainting. A pacemaker can help a person who has an abnormal heart rhythm resume a more active lifestyle. 

“An ICD is a small device placed in your chest or abdomen if you have an irregular heartbeat or are at risk for sudden cardiac arrest. It sends electrical pulses or shocks to the heart when it senses any abnormalities in heartbeat. For example, if a patient with an ICD has an irregular heartbeat or goes into sudden cardiac arrest, the device will send a shock to the heart to restore normal heart rhythm. ICDs can be life-saving, as cardiac arrest can cause death within minutes if not treated.

“The biggest difference between an ICD and pacemaker is that an ICD continually monitors heart rhythm and can send low- or high-energy electrical pulses to correct an abnormal heart rhythm. ICDs will initially send low-energy pulses to restore heart rhythm, but switch to high-energy pulses when the low-energy shocks are ineffective.

“Pacemakers, however, only give low-energy electrical pulses to restore regular heartbeat.

“Therefore, ICDs are more effective in patients at high-risk for or with a history of sudden cardiac arrest, who may need these more powerful, high-energy electrical pulses to restore their regular heartbeat.”

Most newer ICDs can act as both a pacemaker and a defibrillator. Many can also record the heart’s electrical patterns when there is an abnormal heartbeat, a useful tool when planning future treatment.

An ICD can be programmed for these therapies:

  • Low-energy pacing therapy. You may feel either nothing or a painless fluttering in your chest when your ICD responds to mild disruptions in your heartbeat.
  • Cardioversion therapy. A higher energy shock is delivered to deal with a more serious heart rhythm problem. You might feel as if you’re being thumped in the chest.
  • Defibrillation therapy. This is the strongest form of electrical therapy used to restore a normal heartbeat. During this therapy you may feel as if you’re being kicked in the chest. It may knock you off your feet. The pain from this therapy typically lasts only a second. There should be no discomfort after the shock is over.

♥  ♥  ♥

UPDATE: Watch this helpful video (about 7:20) by Doug Rachac, who has become my go-to resource for questions about implantable devices. Doug worked for Medtronic (a company that manufactures these devices) for 14 years, and then became an ICD patient himself. 


* Long QT Syndrome: An inherited defect in heart rhythm that predisposes to sudden fainting spells, dizziness, palpitations, seizures and sudden death. The heart takes longer to recharge itself between beats. Certain conditions can trigger an abnormal cardiac rhythm. Among the known triggers for Long QT are intense physical exercise, swimming, being suddenly startled or badly frightened.

It’s estimated that 4,000 children and young adults die yearly of Long QT. It is a common cause of sudden death among school athletes, as well as the cause of many unexplained drownings. The first sign may, unfortunately, be sudden cardiac death. The heart muscle abruptly goes into fibrillation, beating too fast and so ineffectively that the blood stops circulating. The heart has to be defibrillated (shocked back into a normal rhythm) within a few minutes if the person is to survive. Early diagnosis is essential. Drugs called beta blockers can help to maintain a normal heart rhythm in many cases. In the remaining cases, a pacemaker can be implanted to set the heart’s rhythm, or an implantable cardioverter defibrillator can be put in that can help to detect and correct an abnormal heart rhythm.


See also:

19 thoughts on “Do you know the difference between a pacemaker and an implantable defibrillator?

  1. Dear Carolyn
    Thank you so much for this article on ICD and Pacemaker – my husband had a bad heart attack back in February this year and he has now been told he will have an ICD fitted. I was worried as I thought for his condition the pacemaker would be better from what people were saying but THANK you so much for clarifying what the doctors should have.

    I am very grateful to know people like you are around to help us lay folk understand.

    Liked by 1 person

    1. Thanks for your kind words, Flora – but it’s upsetting to know that your husband was not fully informed by his doctors about his upcoming ICD procedure. This is a scary scenario for anybody to imagine, and yet patient education is often woefully absent.

      Make sure to ask the doctors lots of questions about the ICD procedure and follow-up, and do not leave the doctor’s office until you’re comfortable with what you hear. Good luck to your husband (and to you!)


  2. What an amazing, informative, to the point, and perfect explanation between an ICD and a pacemaker.

    I’m a nurse and could NOT have explained it better.
    I will forever now just hand copies of this article to my cardiac patients, instead of trying to explain the difference between the two devices myself. lolol.
    Thank you.
    Debbie Q., RN
    Hudson Valley, NY

    Liked by 1 person

  3. Its very interesting to know the difference between a Pacemaker, and a ICD.

    My Brother is having a ICD Device implanted, and we had a discussion about Pacemaker’s and Defibrillator’s.

    There was confusion over how the two devices worked to treat irregular heartbeat conditions.

    I did explain that the two devices worked differently, but was unsure how?

    The information you have provided is very helpful, and it gives us the medical knowledge to understand how these two different Devices work when Implanted.

    Thank you so much for the information.


  4. Hi. My name is Gabriela and I am in my last year of college. I have to make a thesis about “Exercises allowed to pacemaker carriers”, and I was wondering if you could share with me your life from the moment you got this device until now. By this I mean if you did physiotherapy after surgery, what kind of exercises were you recommended, what you shouldn’t practice and what is your heart beat before and after a moderate effort. I hope you can see my message and I look forward to hearing from you.

    Liked by 1 person

    1. Hello Gabriela – I don’t have a pacemaker implanted so cannot answer your questions. Perhaps some of my readers will see your request and share their personal experiences with you. Meanwhile, you could ask Dr. Google the same questions. I just did a quick search and found lots of links. Good luck to you…


  5. Can you tell me a little about this please I did have open heart surgery because I was born with a hole in my heart. I got it corrected a few years ago. Doctors told me its a mechanical valve that ticks inside of me. They also told me that I need to take warfarin for life. Can you all help me understand this. Thanks


    1. Hi Madeline – the main difference is whether the patient is at risk for sudden cardiac arrest or not (that’s when an ICD is considered). Re-read the first couple paragraphs quoted from the American College of Cardiology to remind yourself of the basic differences.


  6. I too had never heard of ICDs – right up until the day I had one implanted. Thanks for this very clear explanation of these two life-saving devices.

    Liked by 1 person

  7. This is definitely a helpful, clear explanation between the two. However, as heart disease survivor with an ICD, I have to laugh at the term “small device!” When you are a small framed woman, they have to cut your breast muscle to insert the device. It may be only an over-night hospital procedure, but I was in severe pain for a year, with no empathy for help from the surgeon. Now, almost 3 years later, it still causes pain and soreness when I work out. Stretching and yoga helps, but definitely was on my own in figuring out how to cope.

    Liked by 1 person

    1. Hi Stephanie – yes, I think when doctors use the word “small”, it’s a relative term, isn’t it? I know a number of women with ICDs, and those with soft, rounded shapes seem to adapt a bit easier. Your surgeon sounds like a person who’s never personally had a breast muscle cut open . . .


    2. Stephanie, maybe you can answer for me about the exercise and yoga: I work out but it is uncomfortable, so that is kinda normal? Thanks for your help.

      Liked by 1 person

    3. Yes I had a 2nd pacemaker inserted. It’s quite big, I have a small frame and it moves about in my chest especially when I bend. When I mentioned this to the surgeon, he just said put on more weight! Do the symptoms improve with time?

      Liked by 1 person

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