What I now know about ICDs
- Apr 26, 2024
- 4 min read
I got my implantable cardioverter defibrillator (ICD) implanted in June 2022. That is now almost two years ago. That blows my mind a little bit.
Every time I see a cardiac tech, I still learn something new about my ICD.
What is an ICD?
Most people will be aware of pacemakers as an implanted device to help the heart beat faster. An ICD is similar to a pacemaker in that it is an implanted device, but it's main purpose is to help slow down the heart when it beats too fast. I had never heard of am ICD before either..
I got my ICD in June 2022. I haven’t had to replace the battery yet. I think that happens on average every 7 years.
Leads
There are different types of ICDs. The main differences are how many leads they have and what kind of pacing they will do.
I have a single-lead ICD connected to my lower left chamber of my heart - the left ventricle. The main purpose of my ICD is to pace my heart into a lower rhythm when it detects that my heart has started beating too fast. It can do pacemaker pacing as well, but it is not meant to do this long term.
I have mainly had fast rhythms. 130 beats per minute. 185 beats per minute. 200 beats per minute. My ICD has treated these by pacing me and also shocking me.
Some other cardiac sarcoidosis patients have what is called a CRT-D. That is a different type of ICD with three leads. Two of the leads are for pacing slow heart rhythms, and one for fast heart rhythms. CRT-Ds are needed by people who have complete heart block with arrhythmias.
Luckily I have not gone into complete heart block. I do have AV block, but it only went up to second degree. And it's back down to first degree now. So my single-lead ICD is perfectly fine for me.
You will know you are in complete heart block if your resting heart rhythm is really, really low. Under 40 beats a minute. Please confirm this with your doctor though. I am not a medical professional.
What does a shock feel like?
When I got the ICD, the nurse said a shock would feel like a horse kicking you on your chest.
I have been shocked 5 times. Each time has been with a Ventricular Fibrillation (VFib) rhythm of over 200 beats per minute. When your heart beats that fast, your brain gets starved of oxygen. I lost consciousness within seconds each time, and have never felt a shock.
I would just wake up on the floor with a slight pain in my chest. I feel very lucky not to have felt any, to be honest.
Magnets
One of the first things I was told in the hospital in preparation for getting my ICD was that magnets can interfere with it, and that I need to avoid magnets.
The nurse who gave me an overview of the ICD told me about a few everyday things that might have magnets in it:
Anti-theft devices at shop entrances
Phones with magnets for wireless charging
Wireless earphones with magnets.
I am also not allowed to interact with a car battery and jumper cables, or do any ARC welding. Such a pity! 🤣
Some medical equipment like MRI machines also have magnets. If I need to get an MRI I need a cardiology team on standby to turn my ICD off temporarily, and to make sure they can shock me with an external defibrillator if an emergency occurs during the MRI.
Anti-Tachycardia Pacing (ATP)
When your heart beats too fast, but before it gets to the point of a shock, the ICD will try to pace the heart down into a safe rhythm. This is called anti-tachycardia pacing or ATP.
For a really detailed technical article on how ATP works, take a look at
I can feel this pacing when it happens. In general I also feel a wave of dizziness or weakness when my heart rhythm goes high enough for this to kick in. The pacing happens within seconds, most of the time. It feels like - and this sounds worse than it probably is - my heart is being flicked with an elastic rubber band a few times in a row.
Normally I will feel 3 flicks in a row, and then a pause. If the pacing hasn't worked, it will repeat until it does work.
Zones
My ICD has different heart rate zones for monitoring, pacing and defibrillation.
My pacing zone is now set to 150. When I first got my device, it was set to 180. This has been lowered over the last 2 years to suit my heart and the fast heart rhythms where I am feeling symptoms like sweating and dizziness.
My defibrillation zone is set to start at 220. If I have a VT arrhythmia that shoots over 220 beats per minute, my ICD will shock me.
The monitoring zone is where the ICD will record the heart rhythm and send it to the ICD monitoring team, but no pacing or shocking takes place. This is set to 135 for me.
Morph match
An ICD doesn't just pace or shock based on heart rate. It also checks if the heart rhythm pattern (morphology) matches a dangerous heart rhythm pattern. This is called morph match and the sensitivity of the matching can be set to best suit your heart.
That is pretty cool!
Reprogramming the ICD
If for some reason my ICD's settings need to change, I go to the hospital to see the ICD tech team. They wheel out a computer, and hold a device over my ICD. This device connects to my ICD from outside my body, and allows the tech team to change settings without touching the device. Almost like a Bluetooth headset to your phone.
Feel free to message me if you have any questions.
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