Pacemaker changes ?

Good morning all ! i had an MRI yesterday on my foot, an issue I've been dealing with for 20+ years. The Medtronic rep came to put my pm into " safe " mode. I told him and the MRI tech that I guess I was  anxious -rapid heart rate - not with the MRI- but with anything pertaining to the PM. The rep made his adjustments and they took me in to get the MRI. I was getting hooked with etc. when the rep asked how long my procedure would take and he was told about an hour and 15 minutes. On hearing this, he asked them to bring me back out and he said he put on " scan." On my PM.  He said he didn't want my intrinsic heart beating that hard for an hour and 15 minutes. My heart rate finally slowed and eventually  The MRI finally was completed, He told me he was resetting everything as it was and I asked him for a print copy. Last device check in late January, here's what a few of my setting were... 
impedance Atrial 494; now it's 551.    Ventricular lead was 437, now 456

Capture Threshold in January Atrial, 0.625V @.40ms. In ventricle, 0.25v@.40ms

March 26 setting: 0.875@.40ms Atrial and 1.250 V@.40ms In the ventricle.

Amplitude/ Pulse width in January 150 V/.40ms Ventricle 2.25V@.40ms

March 26, 1.75V@.40ms. Ventricle 2.50 V@.40ms

sensitivity was unchanged : atrial .30 mv and ventricle .90 mv

Pacing percentages weren't listed on the sheet. 
I'd appreciate any thoughts any of you who understand more of this than I do !


I have a dual chamber PM with intermittent 2 nd and 3rd degree Heart block. I feel great and been doing well since I got my PM in 2020.

Thanks again



Hello Dixie Chick

by Gemita - 2021-03-27 10:44:03

Love the new name!  Your last fews words said it all "I feel great".  This is really most reassuring.

I will leave others more qualified to answer this, but I just wanted to say some of these figures will change over time naturally.  Mine certainly have and I have not had an MRI.  I would advise you to phone your EP though on Monday for peace of mind and discuss the significance (if any) of these changed values and ask whether your MRI scan may have caused any capture difficulties or whether this is all pretty normal stuff?  A quick visit to the pacemaker clinic for a few additional checks would do no harm in my opinion.

I am glad otherwise you suffered no ill effects from your MRI.  Take care and please try not to worry but thank you for reporting your experience.  I really hope the MRI will help your doctors to heal that foot of yours

Not easy to follow the numbers

by crustyg - 2021-03-27 12:06:50

Lead impedances haven't changed significantly, capture thresholds are good, sensitivity is good.

*IF* I understand the numbers correctly he hasn't put your PM back to exact same settings that you had in Jan, for good reason.  If I take the numbers at face value, you *appear* to have a failing vent lead: vent-capture threshold 0.25V 0.4ms in Jan and now 1.25V 0.4ms - that's a big increase in threshold.  DO NOT PANIC!

However I *suspect* that there's a typo in the Jan capture - else why would you have had a pacing output of 2.25V 0.4ms in Jan.  If it's now 2.5V 0.4ms then that is an increase - which doubles my suspicion that the Jan vent-capture threshold wasn't 0.25V but was 1.25V.  In fact, I don't think you (or anyone else) can achieve capture at 0.25V - it's simply too low to overcome the normal electrical potential of a cell.  I had to greatly enlarge my browser to spot the decimal point for the pulse-width values - and it's missing in one instance.  Usually PMs deliver a very short output pulse - less than half a millisecond - to save battery power.  It's helpful to always start with a 0 in front of a decimal point 0.4ms rather than .4ms.

OK, the above demonstrates all of the dangers of remote 'diagnosis', and I've probably given you a fright.  The numbers aren't *bad*, but *IF* there's a trend upwards for your vent-capture threshold, then this needs to be watched.  How often are you reviewed?

Many contributors here will re-emphasise that if you feel good (apart from the foot problem) then carry on enjoying life and let your EP-team do the gentle worrying about that vent-lead.

Was there a particular reason why you shared your numbers?  Has someone made a comment about your PM or leads in your hearing?

BTW, I know that you can edit your post (if I'm correct about the putative typo) - I've made a screenshot...

Best wishes.

PM changes

by Dixie Chick 65 - 2021-03-27 12:28:28

Thanks to Gemita and Crusty for your responses...

I had thought about calling my EP’s office on Monday, Gemita. However, since I feel good and no issues I wouldn’t want to appear “ neurotic” so I’m going to hold off unless something changes ! 

Crusty, I guess the reason I shared to numbers is because I also had doubts about the Ventricular capture numbers in January. I asked him for a copy of the interrogation and he gave me 3 pages. Then the doctor struck through 1.125v @0.40ms and wrote in 0.25v. So maybe in his haste he left out something. I’d attach a picture if I could ! At any rate, I think I’m doing well and don’t want to rock the boat too much. My pacing percentages then were 14.8% Atrial and 0.2% Ventricle, which is pretty good. Of course that could change quickly and I’m sure my Heart Block will do Just that. But with my PM in place, I’ll be prepared !!!

One reason I like this site is that I can get such good advice for free !! Without bugging my doc ! Lol. 

Thanks again, I really appreciate it.

Try sending a pic to the gallery

by Gemita - 2021-03-27 12:41:54

Dixie Chick you could try sending a pic to the gallery blanking out personal details??  I am glad you feel reassured

PM changes

by Dixie Chick 65 - 2021-03-27 12:49:16

Good idea, Gemita. I’ve never posted to the gallery but I’ll see if I can do that.

PM interrogation

by Dixie Chick 65 - 2021-03-27 13:13:18

Well, Gemita, I was able to post it - In fact, I posted it twice !! Sorry, not sure how I did that. Tried to take one of them sown and couldn't Thanks for the suggestion !


Don't do anything more, I will delete one for you

by Gemita - 2021-03-27 14:04:10

Well done Dixie Chick !!  We are all having to learn fast on this forum

Update okay deleted one copy 

Guess nearly right

by crustyg - 2021-03-27 14:29:11

1.125V - clear as a bell.  Whatever was going through the Doc's mind when this was struck through and replaced with 0.25V wasn't the real value.  I commented that I didn't think it possible to capture at this low voltage just using my remembered physiology from a lifetime ago.  A quick search online suggests that I was correct.

Anyway, the numbers are OK.

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My pacemaker was installed in 1998 and I have not felt better. The mental part is the toughest.