What is the Difference Between a Pacemaker and an ICD?

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  • Written By: Mary McMahon
  • Edited By: Kristen Osborne
  • Last Modified Date: 21 September 2019
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Pacemakers and implantable cardioverter defibrillators (ICDs) are both devices used to address heart conditions by shocking the heart internally when a problem develops with the heart rhythm, but a pacemaker and an ICD are designed for different purposes. The pacemaker helps to regulate the heart beat, keeping the rhythm stable, while an ICD is designed to shock the heart specifically when it is beating dangerously fast, a rhythm known as fibrillation. Cardiac fibrillation is very dangerous and can cause death if it is not rapidly addressed; the ICD acts as an internal version of the shock paddles used by physicians.

The key difference between these two devices is the function the device is designed for. Both monitor the heart rhythm continuously so they can activate if a problem develops, and they are somewhat alike in size and design. The installation procedure is also similar, with leads being attached to the heart to monitor rhythm and deliver shocks, while the pacemaker or ICD impulse generator is implanted nearby.

Some patients need a pacemaker and an ICD. Their hearts slip into abnormal rhythms periodically and require pacemaking to beat regularly, and they are also at risk of fibrillation. These patients can have a combination pacemaker/ICD device implanted to perform both functions. Other patients just need one device, such as an ICD in a patient with a history of fibrillation or a pacemaker in a patient with an abnormal heart rhythm.


Both devices can save lives by regulating heart rhythm or stepping in when a patient is on the verge of a myocardial infarction. They are implanted in patients of all ages all over the world on a regular basis. Once implanted, the patient must regularly check the device to make sure it is functioning, and periodic follow-up appointments in a medical office are needed for both a pacemaker and an ICD. In both cases, the patient's heart rhythm is checked and the device is tested to see if the batteries are still functioning. On some models, data can also be retrieved to return information on cardiac events of interest to the patient's care provider.

Both a pacemaker and an ICD can be a good management option for a variety of heart problems. Patients with these devices can return to normal activity levels around six weeks after implantation and may experience improved quality of life, as well as a better prognosis, once the device is installed and functioning.


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Post 3

Does anyone know what the effects are of smoking marijuana while in a state of "chronic fibrillation?" I know this question sounds stupid, but I need to have others' opinions because my husband is just saying I don't "want him to be comfortable" after his emergency valve replacement last Christmas Eve, which gave him the chronic afib. Please someone, answer! I don't think he is in his right mind and may be suicidal.

Post 2

@SZapper - From what I gather, these devices don't malfunction often. I imagine if they did, they probably wouldn't be approved by the FDA for use in humans!

I think it's really neat the device can save info for the doctor to review. I think something like this could totally be the future of medicine in other areas besides the heart.

If you could implant something to monitor a patients condition and give information to the doctor, I think it would help in the treatment. If the doctor knew exactly what was going on in the body I'm sure that would make it easier to tailor medical treatments to each patient.

Post 1

An ICD sounds like it could be really scary if it malfunctioned. I understand that there is sometimes a reason to shock the heart, but I think it could be dangerous if there was no reason or if the device starting shocking uncontrollably or something.

I guess what I'm saying is that I'm glad to know patients that have these gadgets get regular checkups!

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