MRI with Pacemakers : II – 3T-MRI with Dual Chamber Leadless Pacemakers

• by brady
• 2023-03-17 11:59:32
• General Posting
• 93 views
• 2 comments

In Mid March 2023, I had 3T-MRI scans with and without contrast on the brain then on the abdomen. The former was successful but the latter had failed due to excessive motion.

The MRI scans were done in the radiology department of the same hospital where I had my implant. When I arrived at the hospital, I was surprised to find not only two research representatives from electrophysiology department were there but also the Abbott engineer who is responsible for the clinical trial.  But the EP was not there, which was expected.

The engineer then interrogated the PMs. I asked for a copy of the printout but I was careless and didn’t notice that he didn’t measure the threshold voltages (he used the one measured in the last followup in January).  He asked me what mode I preferred to be programmed to during MRI. I had done my research. I said turned it off because I was not pacemaker dependent. When that was done, my heart rate initially dropped to 30bpm, but later increased to 38-45 bpm throughout the MRI scans.

Beside the MRI technician, a nurse was also there. She hooked me up to an EKG machine and IV drip (for the dye); also put an oximeter on my finger.

So the life support was in place to do the MRI scans.

During the head scan, an RF coil was put over my head and a blanket like RF coil was put over the abdomen. The movement of the head was restricted by foam pads, but there was no restriction on the abdomen.  According to literature, the specific absorption rate (SAR) for the head could be as high as 3.6 Watts/kg whereas else in the body could be 2 Watts/kg.

There were 4 scans. Each scan took about 15min. The total time was one hour. I received the radiologist report within 20 min. The MRI brain scan was successful. However, for the abdomen, because of the earplugs and my poor hearing, I couldn’t hear “hold your breath” well. The abdomen scan was no good because of excessive motion. I went back to ask the technician and he said it was common for the abdomen scan to have excessive motion.

If the tech were more competent, I would have a better chance of getting a good abdomen scan. He should have had me checked out the sound system to see if I could hear the instructions. The noise comes from the RF coils. It would be better not to do 4 scans all at once, but to pause between the brain and abdomen scans. After the brain is done, stop the scan and remove the head RF coil and remove the earplugs. This would allow the patient to hear more clearly the weak sound instruction.

It is easy for the abdomen scan to fail because there is nothing to restrict the motion of the abdomen. It would be difficult to stay put throughout the ½ hour scanning time.  But I ddn’t know this before the scans. Another option would be go for a CAT scan instead of MRI.

After the scan, the Abbott engineer restored the pacemakers to their original settings. The performance of the pacemakers were interrogated once again to make sure they were fully functional. I also got a printout.

The pacemaker parameters before and after are as follows.

Battery longeivity: 

RA 7.5 yr, RV 14.0 yr Before MRI

RA 7.2 yr, RV 14.1 yr  After MRI

Threshold voltages:

RA: capture  0.5V@0.4ms, sense 1.4mV, impedance 390 ohm Before MRI

RA: capture  0.5V@0.4ms, sense 1.7mV, impedance 360 ohm After MRI

RV: capture  0.5V@0.4ms, sense 7.9mV, impedance 570 ohm Before MRI

RV: capture  0.75V@0.4ms, sense 9.3mV, impedance 580 ohm After MRI

Pacing voltages:

RA:  1.25V@0.2ms, sensitivity 0.5mV Before MRI

RA:  1.25V@0.2ms, sensitivity 0.5mV After MRI

RV:  1.25V@0.4ms, sensitivity 2.0mV Before MRI

RV:  1.25V@0.2ms, sensitivity 2.0mV After MRI

Pacing frequency

Atrium:  AP >99%, lifetime 97% Before MRI

Atrium:  AP >99%, lifetime 97% After MRI

Ventricle:  VP <1%, lifetime 5% Before MRI

Ventricle:  VP <1%, lifetime 5% After MRI

From the above, the notable parameter changes are the ventricular threshold voltage has increased 0.25V  and the atrium battery lifetime has decreased from 7.5 to 7.2 yrs.  I am concerned about these two degradations and thought that if I had done the brain and abdomen scans on different dates, the degradations might not have happened.  And I hope that the increase in threshold is transient.

In summary, MRI with a pacemaker is a serious matter. Full life support needs to be there for the scan to be carried out. During 3T-MRI of one hour, my leadless dual chamber pacermakers seemed to have no major issues except the ventricle threshold had increased 0.25V, and atrium battery longevity has decreased by 4 months, both are undesirable and concerning.   In hindsight, it was unwise of me to do 4 scans in a single visit. The risk was unnecessary.

To be continued…..