MRI with Pacemakers : I – Background
- by brady
- 2023-03-16 16:59:29
- General Posting
- 155 views
- 6 comments
This and subsequent posts are only for people who want to do MRI and also want to understand the risks and the various details of MRI.
I had a pair of Abbott dual chamber leadless pacemakers implanted in September 2022 and just had 3T MRI brain and abdomen scans in March 2023. The pacemakers are still in clinical trial.
MRI in people with pacemakers conjures up an image of a life saving, delicate and sensitive metal device placed in a very strong magnetic field. This raises serious concerns.
Currently 1.5T, 3T and 7T MRI are available. For the leaded pacemakers, there are many studies. Some of them had several hundred patients and almost all used 1.5T, except several small studies, that used 3T. However, for the leadless pacemakers, there is only one study with 15 patients, 7 for 1.5T, 7 for 3T and 1 dropped out. So to understand MRI with Pacemakers, I have to consult publications on leaded pacemakers.
Because my dual chamber pacemakers are still in a clinical trial, for the last several month, I had been struggling to obtain permission to do MRI.
At first I contacted the company, which said it would not approve my MRI. Later during followup, the Abbott engineer told me that “off label” Abbott would not approve MRI, but the electrophysiologist could overwrite the decision and “off label” approve it. I then contact the hospital’s radiology department, after much effort, it approved me doing 1.5T, but would not approved 3T, claiming the clinical trial leadless pacemakers were “incompatible “ with their 3T machine.
During these months, I have been collecting and reading scientific publications on MRI with pacemakers. I used what I had learned and wrote to the chairman of the radiology department arguing that scientific evidence showed the leadless pacemakers were safe to be scanned by 3T MR. Finally, he relented and gave me permission to go ahead.
In the next several posts, I wish to share the information I have collected from publications so that others could start their research based on what I have found instead of starting from scratch. Some of the information would be redundant because I wanted to present the different views from different researchers so that the readers could have a more comprehensive views of the topics presented.
Before I started the current research, in a previous post I had said that for MRI, leadless pacemakers have advantages when compared with (conventional) leaded pacemakers. At that time I was insensitive without realizing that almost all the readers and members of this forum had leaded pacemakers. My apology for being so insensitive. The insensitivity had invited a reader to imply that I worked for the leadless industry. No, I do not and have not worked for any leadless pacemaker industry and I sincerely hope that members and readers of this forum could accept opposing opinions. We can have a debate on the scientific merit of the opinion. If I make any errors, please correct me, but please, no more accusation.
Based on the results of current research, the statement that for MRI, leadless pacemakers have advantages over the leaded pacemakers was and is correct because leadless pacemakers generate less heat at the tips of electrodes than leaded pacemakers ( ref 1-3)
Also the leads could experience a force and torque (ref 3) whereas the leadless has no lead except the hollow titanium can.
Although the comparison is not side-by-side so it is not definitive. The size of a leadless pacemaker is a fraction of a leaded pacemaker. From the size perspective, it is fair to say that leadless pacemakers will have fewer concerns in MRI than leaded pacemakers.
To be continued…..
“In a non-perfused model of the right ventricle, the temperature rose less than 0.4C at 1.5T and less than 0.5C at 3.0 T. These increases in temperature at the device–tissue interface were deemed negligible and safe and to be even lower in a real, blood perfused right ventricle.7” “Monocenter Investigation Micra MRI study (MIMICRY): feasibility study of the magnetic resonance imaging compatibility of a leadless pacemaker system” Hermann Blessberger et al.
“Roguin and colleagues tested the temperature of pacemaker lead tips and ICD coils both in vitro and in vivo: the temperature increase noted at the tip of the leads in vitro was up to 7.0 °C and less than 0.2 °C in vivo. The increase in temperature did not meet clinical significance, defined as a change in temperature of at least 8 °C . In these studies, the extent of change in temper- ature measurements was noted to vary based on scanner type, as well as structural features of the lead, including length, insulation, proximity to scanner, and the coil . “Magnetic resonance imaging safety in patients with cardiac implantable electronic devices” Eunice Yang et al.
“Results: For in vitro testing, the maximum translational force was 2150 mN (mean, 374.38 mN +/- 392.75 [standard deviation]), and maximum torque was 17.8 x 10(-3) N x m (mean, [2.29 +/- 4.08] x 10(-3) N x m). The maximum temperature increase was 2.98 degrees C (mean, 0.16 degrees C +/- 0.45).” “Safety of brain 3-T MR imaging with transmit-receive head coil in patients with cardiac pacemakers: pilot prospective study with 51 examinations” Claas P Naehle et al.
There are much better reasons to prefer leadless to leads for MRI
by crustyg - 2023-03-17 06:56:04
Your data shows very nicely that lead heating during MRI in real patients is not a significant concern for modern MRI-compatible leads.
Leaving aside issues of heating and magnetic fields (the great red herring for MRI, as no part of the PM/lead assembly is ferro-magnetic), the artefacts from metal objects in MRI (and CT) scans is a significant problem. There are some contributors here who've had repeated studies to try and assess if an RV lead has penetrated, or even punctured the RV (the latter is usually clinically obvious), but the scan detail around the lead tip can be very poor with extensive flare obscuring the important information.
by piglet22 - 2023-03-17 07:49:58
Not much that I can add and well done for digging out all that information.
It must have been hard work.
There's that well worn phrase used before any operation, "this procedure carries some risks", before you sign the consent form.
Gemita, crustyg and piglet22: Thank you all for your comments!
by brady - 2023-03-17 17:22:58
Hello Gemita, crustyg and piglet22,
Thank you all for your comments!
I read some your recent posts. They are full of useful information. It is wonderful that all this time you have been helping other members with your experience and knowledge.
I tried to use URL for references as you had suggested. But some of the URLs are very long, so I didn’t do it.
You mentioned “as no part of the PM/lead assembly is ferro-magnetic”. Are you sure that is the case?
I have been looking for this answer for a long time. My current understanding is that in the battery there is a voltage doubler circuit (presumably a step up transformer) that still use a ferromagnetic core. For some reason, that could not be designed out. But I am not sure I am right.
by AgentX86 - 2023-03-18 15:49:22
Voltage doublers don't use transformers, rather switched capacitors. "Voltage doubler" is a specific type of circuit and may not be precise in this context. A step-up, or "boost converter" would use an inductor. There are other circuit topologies, some that use transformers but they're normally used for a lot more current (as is the boost converter).
In short, it's possible to avoid magnetic materials in such power supply. Not having designed a pacemaker, it's hard to know all of the design trade-offs. In fact, I don't know that a voltage higher than the battery is necessary (in an ICD, it could easily be, just to store the energy).
No more ferromagnetic material in pacemakers?
by brady - 2023-03-18 16:37:49
Thanks and I am glad to have an answer from a member who has electronic design background!
I had searched many scientific publications asking since the PM design changed to make them "MRI conditional" in 2011, how much ferrromsgnetic material is still used in current pacemakers. The answer I found was,the voltage doubler in the battery circuit may still use ferromagnetic material.
if you are correct, then crustyg is correct, modern pacemakers do not contain any ferromagnetic.
my research also found that pacemakers need a voltage doubler. The lithium iodine battery output votage is 2.8V. Some people have a capture threshold 2V or more. With a safety margin of 2X, that means the pacing voltage needs to be >4V. The voltage doubler drains the battery more quickly shortening lifetime.
You know you're wired when...
You have a maintenance schedule just like your car.
Hang in there; it does get better every day!
Having an MRI with a pacemaker
by Gemita - 2023-03-17 06:51:57
Hello Brady, thank you for taking the time to post again on this vast subject and for sharing your extensive research with members, particularly members with leadless pacemakers. I am sorry you had such a struggle to get your recent MRI.
I am certainly not concerned about getting an MRI with my 2018 dual lead pacemaker implant, although it is still quite difficult to get an MRI unless we attend a main hospital where radiographers have experience dealing with pacemaker patients and where cardiac technicians are on hand to place pacemakers into a safe mode for the duration of the scan.
I hope the results of your MRI scans will bring reassurance and not find anything too worrying? I hope too your scans didn't cause any dificulties with your pacing? I hope as well you are making good progress with your dual leadless pacemaker?
When you post in future, rather than typing extracts from a Research Paper, it is always best to post the link(s) for the entire paper(s), so that members may read for themselves and form their own opinion of the findings, although I am grateful for the References 1-3 that have been provided to save valuable time.
I have attached a couple of links myself which might be helpful too which should be copied and pasted into our main browser to open.
Welcome back Brady