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Patient Beware: MRI-Safe Pacemaker Precludes Ga68 PET/MRI Scan at UCSF

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Posted 9/29/2017 10:22 PM (GMT 0)
Recently had a pacemaker installed (Medtronic "Sure-Scan" OK for 3T MRIs). Before surgery, I clarified with the surgeon that I am a prostate cancer patient who will likely be getting many scans and it was very important to me to be able to have MRIs to avoid the massive ionizing radiation of whole-body CT scans. My urologist and radiation oncologist like Ga68-PET/MRI scans. A few days after my pacemaker surgery, I checked up on the scheduling of the Ga68-PET/MRI scan ordered by my radiation oncologist. I was told that UCSF could not and would not provide that to a patient with a pacemaker because the facility at UCSF where they jigger up the Ga68 tracer and do the combo PET/MRI scans does not medical personnel on hand to monitor a pacemaker patient or a Code Blue capability in case something goes wrong. So it turns out that I can have MRIs at UCSF, just not the MRIs I need as a cancer patient at UCSF. The electrophysiologist who told me I'd be able to have MRIs with the pacemaker tried to work this out with the medical safety czar, but I think I'm stuck with a choice between getting a PET/CT or going somewhere else if I want a Ga68 scan.

I have two questions:

1. How leery should I be of the CT component of a PET/CT? Per Consumer Reports (a frequent source of misinformation, but what the heck?) "CT emits a powerful dose of radiation, in some cases equivalent to about 200 chest X-rays, or the amount most people would be exposed to from natural sources over seven years."
Getting CT scans sounds like a nasty habit to get into, but, of course, I already have a nasty disease that may cash me out before anything else gets to me. (Doctors see me as a young and vigorous 68 with a potentially long lifespan. The pacemaker is supposed to help my biking up steep hills without arrhythmia dragging me down.)

2. Is there a place besides UCSF where I could get the Ga68 PET/MRI? I'm willing to get on an airplane (a chance to soak up more of that ionizing radiation), but the facility would have to willing to scan a "Sure-Scan" pacemaker patient.
Posted 9/30/2017 1:07 AM (GMT 0)
All places that offer a PET/MRI offer a PET/CT too. In fact, there are only about half a dozen Siemens PET/MRI machines in the US (UCSF being one of them) that give simultaneous acquisition of PET and MRI images. GE and Phillips make versions that take consecutive images. You can also just hop from a PET/CT to a separate MRI and then fuse the images. But why not just get the Ga-68-PSMA-11 with the ordinary PET/CT there? The difference should not make a difference - what purpose do you want it for, anyway?

1- the radiation delivered by a CT is negligible compared to the IGRT/SRT you already had. In fact, if you had the SRT at UCSF you had a cone beam CT before each one of your 35 or so treatments, totalling to less than 1 Gy of additional absorbed Xrays.

2-It is unnecessary to have a PET/MRI when a PET/CT would probably suit your purpose (whatever it is) just fine. You can contact Siemens to get a list of operating PET/MRIs in the US. I know MSK, JH, Mass General, Stanford, Cleveland Clinic and Washington University has it. JH only offers the DCFPyL PET, which is more accurate than the Ga-68-PSMA PET. You can call to see if they'd be willing to use their PET/MRI on you, but more likely they'd just recommend the PET/CT.
Posted 9/30/2017 4:45 PM (GMT 0)
When I had the nano-iron MRI in Nijmegan, the Netherlands, Prof. Dr. Barentz told me of another patient from Chicago, one who had a pacemaker. Dr. Barentz did not want to do his 3T MRI on him, but the fellow was wealthy so he flew to Nijmegan (in his private plane), got the infusion, then both flew back to Chicago to have the MRI at some place here that already knew the patient.
Posted 9/30/2017 11:36 PM (GMT 0)
My pacemaker is not MRI-compliant, so I never planned on any evaluation that required MRI. I did, however, have a CT scan for radiation planning, and there was absolutely no problem. I also had 5 SBRT treatments with no issues.

My pacemaker clinic only wanted me to have a complete pacemaker interrogation before and after the 5 SBRT treatments to ensure that all was well with the pacemaker.
Posted 10/1/2017 12:25 AM (GMT 0)
Thanks, Allen. I understand the 70.2 Gy of SRT delivered to my prostate bed far exceeded the exposure from the cone beam CT, although I'm still curious how the effective radiation exposure (in microsieverts) from either of these exposures compares to the effective radiation from the whole body Ga68 PET/CT (in microsieverts). I couldn't find the answers online, but I gather you are confident that the relative toxicity of whole body CT vs. MRI scans is not really an issue, in which case, I can get back to worrying about my friends in Puerto Rico. A sister of one of my friends has already had her radiation treatments in San Juan interrupted by two hurricanes and is not certain what her doctors will say about the current break of as-yet-undetermined duration. Something to think about for any of us who are struggling with issues our own oncological journeys.

@Cigafred, I think a flight to Nijmegan is not in my future given the relatively minor risk of doing the PET/CT instead.

Thanks to both of you for your responses,
Tomson
Posted 10/1/2017 12:39 AM (GMT 0)
Paxton,

When your current pacemaker battery runs out, you can look into replacing with an MRI-safe pacemaker if it makes sense to you. There are some tasks that are better done with MRI, some better done with CT, although both cover a lot of the same ground. I wanted to be able to do the scans my RO prefers (MRI), but that isn't going to work out. If I ever need imaging other than the fancy Ga68 kind, I can definitely get 3T MRIs at UCSF. My concern about CT was only the ionizing radiation, but, as Allen has explained, that is very little compared to what I've already received from my salvage radiation therapy. I think the general rule is that, if there is a good reason to do a CT scan, the very slight elevated risk of cancer in the distant future is outweighed by the usefulness.

Tomson
Posted 10/1/2017 5:44 AM (GMT 0)
Tomson, replacing an old pacemaker with an MRI compliant one doesn't help, because they only replace the pacemaker unit but not the wires which are by now firmly implanted into the heart.

An MRI would cook your heart!

Incidentally I had problems during my EBRT. I have a Defibrillator (ICD) rather than a pacemaker, but the issues are similar. My ICD was deactivated via a magnet before each treatment and for the first 20 treatments the unit was checked immediately after the treatment to ensure it was ok. It was. They then decided to only check after every 3rd treatment, and you guessed it, somewhere along the way the pacemaker got affected and that impact was not detected. What happened was that the unit got reset to factory defaults which meant that it would activate when it detected a heart rate above 140 rather than the 220 it had been set to for me, (to detect ventricular tachycardia).

The next day when I went for my daily hill climb, I got well above 140 and the ICD activated. Absolutely floored me. Luckily I wasn't too far from home but not before I received 3 shocks 30 seconds apart, until my heart rate dropped below 140.

Caused a great deal of consternation in the cardiac unit and many hours spent in cardiology while technicians reprogrammed it with the help of St Jude experts in the US.

I have since had a Ga68 PET scan without incident.

As the unit has never activated validly (I have had it since 2007) I am seriously considering asking for it to be completely deactivated. With stage 4 PCa, and at 72, I’d rather take my chances on a Cardiac arrest than a prolonged death from cancer - but that is another story.

Chas
Posted 10/1/2017 4:00 PM (GMT 0)
Tomson - chask beat me to the point. I have a dual-lead pacemaker (leads to the atrium and ventricle), and when I was scheduled for my lead revision last summer I discussed MRI's with my electrophysiologist. She reminded me that we would have to change the pacemaker and both leads to get to a MRI-compliant state. She also mentioned that they (Northwestern Memorial Hospital, Chicago) have a couple of radiologists who have successfully performed MRI's on pacemaker patients, even when those pacemakers are not specifically compliant. She said that when the risk of death or serious harm makes that MRI mandatory, they find a way to do it safely.

Since I am not fully pacemaker dependent (when my pacing lead failed last summer, I just felt lousy), they were satisfied with just a full interrogation before the first treatment and after the last. I guess the SBRT was focused tightly enough that the pacer was not affected.
Posted 10/1/2017 6:30 PM (GMT 0)
Oh, you guys are right! I forgot about the leads. I'm still learning about my new "sports appliance." I think of it that way because the only symptom of my arrhythmia was difficulty climbing hills on my bike. Got tired of looking at the back of my regular riding companion's jersey. Turned out my sinus node was kicking out a good pulse, but the ventricles were not getting the message some of the time diagnosed as Wenckebach, Mobitz 1, arrhythmia). My max HR was 90 on a stress test. I'm a little concerned to hear about those shocks when Chas hit the max. My gadget (implanted three weeks ago) was set at 150 max and I've already hit 144 in the gym without going all out. I was afraid to find out what would happen if I reached 150 and now I'm even more afraid. In another week, I was going to start riding and building up to major hill climbs to see whether the pacemaker performs as advertised. Chas's story makes me wonder whether I shouldn't ask them to set a higher max rate before I attack the road. Those shocks don't sound like fun.

Incidentally, Chas, where did you get the Ga68 scans post-ICD? Your plan of deactivating does sound reasonable.

Tomson
Posted 10/1/2017 7:35 PM (GMT 0)
Tomson, I would definitely discuss the triggering rate with your cardio specialist. 150 seems a bit marginal to me. In theory your max HR is theoretically 155, but at age 68 (when I was shocked) I frequently reached 170 when exercising hard, hence my trigger rate being set at 220. But my problem was VT which results in a fibrillating rate way over 200, so safe to set me a high limit. Your circumstances may require different considerations.

Getting unintended shocks is a very unpleasant experience. I was walking up a steep hill when I got the first shock and while it didn't drop me, it stopped me dead in my tracks, the 2nd one did drop me and the 3rd reduced me to a quivering mess. It is not just the pain of the shock, but the scare of “what the hell is happening” that is so debilitating.

I am in Australia and my scan was performed at Nepean Hospital near Sydney.

Chas

Post Edited (Chask) : 10/1/2017 2:18:06 PM (GMT-6)

Posted 10/1/2017 8:22 PM (GMT 0)

Tomson said...
Those shocks don't sound like fun.


I don't believe Tomson can get shocks from his pacemaker. A pacemaker can only send low-energy electrical pulses to restore regular heartbeat. An ICD (that Chas has) is different type of device, it is an implanted heart defibrillator (in combo with a pacemaker) which sends high-energy electrical shock pulses when it thinks it is needed.
Posted 10/1/2017 8:29 PM (GMT 0)
Gemlin, I wondered that too, but was influenced by Tomsons comment that his “gadget” was set to a max of 150. I didn't think a pacemaker had a max setting, only a defibrillator, but I guess Tomson will know exactly what he has.

Chas
Posted 10/1/2017 8:48 PM (GMT 0)
Chas - If it is a standard pacemaker and when the patient is exercising the pacemaker will add beats where needed up to 150. After that it just monitors. The heart is then on its own until it heart rate goes below 150 again. I am sure Tomson knows his "gadget" much better but that is my understanding how a PM works.
Posted 10/1/2017 9:04 PM (GMT 0)
Ah, OK, now I understand, makes sense. Thanks.
Posted 10/1/2017 11:10 PM (GMT 0)
They don't all top off at 150 BPM. Mine is set to a max of 160 BPM, at my insistence. When I first got mine, I would often hit the high 140's to mid 150's under exercise load. I wanted some headroom at that level. Now, some years later, I rarely go beyond the mid-140's -- partly due to the beta blocker I take, and partly due to advancing age and reduced exercise tolerance. I still think I do OK for an old fart. . .
Posted 10/1/2017 11:29 PM (GMT 0)
I don't know my gadget very well, but I have been studying posts over at pacemakerclub.com and I think it really is a problem if the max rate is set too low. I have a/v heart block so the function of the pacemaker is to keep my ventricles paced to what my healthy sinus is calling for. As I understand it, this means that if my sinus rate goes above 150, my ventricles will not keep up and I will, according to many firsthand accounts, not feel good at all. The upper tracking rate for my PM can be set as high as 210 bpm. Not sure why they thought 150 would be adequate for me.

A member of pacemakerclub.com said...
And yes, if your sinus rate is 160-170 and your ventricles are only doing 150 you will most definitely feel it. For me it can be anything from mildly dizzy to black around the edges and feeling like I'm going to pass out to arms and legs like lead. My old pacer (I'm on #5) only went to 170 and I was regularly maxing out so this happened to me several times every workout. It was too frustrating so I eventually went on beta blockers to keep my rate down, then when I got a new one last year they gave me one that goes higher so now it's not an issue. Long way of saying I'm a bit of an expert on how it feels when you max out lol. Yes, the atria can go as fast as it wants. If you are in block, the ventricles are limited to the upper limit.

I'll try to check this out with my electrophysiologist and circle back here with his response in case any other pacemaker guys happen on this thread. I also read one post on pacemakerclub.com that said a Medtronic rep conceded that cyclists are the hardest old farts to please. Sounds like I am in good company.
Posted 10/2/2017 12:06 AM (GMT 0)
That's all good Tomson.

As Gemlin said, it looks like you have a Pacemaker only, without the defibrillator function so it looks like you won't need to worry about unexpected shocks. That is good.

Chas
Posted 10/2/2017 1:02 PM (GMT 0)
Tomson - I'm glad you've joined us at pacemaker club. I don't post much there, but have been a member since getting my first pacemaker in 2011. A couple of related items:

The first time I "outran" my pacemaker I was mountain biking on St. Maartin. I had plenty of muscle left as I neared the crest, but I just ran out of wind. Had to dismount and walk to the peak gasping for breath and on the verge of blacking out. The entire group was wondering if medevac was in my future. I just had to wait a few minutes to re-oxygenate, then completed the ride. Had some settings tweaked when I got home.

Also, when I first got the PM, I was in cardiac rehab. Had no trouble on treadmill, but stationary bike dropped me like a rock. It turns out that my particular pacemaker has two different ways to sense my activity level and exercise load, but only one was switched on. They had the "bounce sensor" turned on, so when I was walking or jogging, the PM sensed activity and raised my heart rate. They had missed turning on the respiratory rate sensor, so while I was riding a bike and not bouncing up and down, the PM failed to recognize activity and did not raise my heart rate.

Also, you should note that many pacemakers will automatically drop your heart rate to about half of your normal rate if they sense your heart rate is going higher than your pre-set limit. Under these conditions they "think" that you are going into atrial fibrillation, hence the "slow-down." I have the t-shirt from this one, too.

Getting a pacemaker set properly for those of us who are "older" but still heavily active can be a challenge. The pacemaker clinicians often see our apparent age and tend toward setting our PM's as they do for the typical old person - which we most certainly are not. We need to have an active dialog with the tech to be sure that they understand our lifestyles and the demands we place on the pacemakers. The devices can be set to work for us, but it is a trial and error task. After all, there are also many younger pacemaker patients who place heavy demand on their PM's, and they do well, so why shouldn't we?
Posted 10/2/2017 7:56 PM (GMT 0)
Paxton,

Right. Even the standard (and much criticized) 220 minus age formula would estimate a maximum heart rate of 152. The electrophysiologist set my maximum at 150 without any idea whether my normal max is 140 or 170. Why would they program the machine to treat 155 as afib?!

On your other point about the sensors, Medtronic does not have respiratory rate sensors but they do have MRI-safe technology. Fortunately, I don't need a bounce or respiratory rate sensor because my sinus node is perfectly fine; the only reason I have a pacemaker is to get the signals from my sinus node down to my ventricles with a suitable delay. Before I understood this thoroughly, I was researching what cyclists were doing if they had pacemakers without the respiratory rate sensors and learned that some were having luck taping small vibrators to their chests and using remote control units to give their PMs a jiggle. Ingenious! Sometimes we just have to do for ourselves.

I'm still not sure how I will feel if I drive my sinus rate past 150 bpm but I am relieved that I'm more likely to experience a leaden feeling in my arms and legs rather than an electric shock. I'm thinking of corresponding with my doctor to see if I can get the limit raised before I start cycling up hills as I don't want to find out when I'm riding alone in a deserted canyon.

P.S. Imagine you felt some grief watching the hurricane beat up St. Maartin.
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