Sudden rate drop

I had sudden onset complete heart block last February and had a pacemaker placed. I've been doing fine, for the most part. This morning I was spinning and my heart rate got up to 167 (I have an Apple Watch and a separate HR monitor) and suddenly my HR dropped to low 80s, I got off the bike and laid down, though I didn't feel bad. After a couple minutes my HR jumped back up to a little over 100, which would be consistent with it coming down 2-3 minutes after stopping. Anyone else ever have that happen? It was a little alarming.


two causes I can think of

by Tracey_E - 2020-11-21 17:22:18

It's possible your sinus rate randomly tanked. Mine does that sometimes, they changed the pacer settings to prevent it. It can come down slowly on its own but if it drops quickly it will pace me to keep my rate up. 

Do you know what your upper limit is? With av block, our sinus rate is usually normal but we need the pacer to make the ventricles stay in sync. It will only pace us as fast as our upper limit. If you hit your upper limit then there is a safety feature to help in the case of afib that will put us in an artifical 2:1 block. That means pacing every other beat which drops our rate in half. If we are in afib and the atria is racing/quivering, then this is a good thing. If we are simply working out and need the higher rate, it's like hitting a wall. If you have no history of afib, this can be turned off. It's also possible you need your upper limit higher. Ideally we want it 10-15 above the highest number we hit working out so we always have a cushion. 

Or if you felt fine, it could be the monitors. Pacers can confuse the heck out of them. Always count manually when in doubt. 

Exercise-induced tachy-arrythmia is another possibility

by crustyg - 2020-11-21 17:49:52

A less pleasant thought is that you had a short burst of an arrhythmia which would make your monitoring devices miss a lot of beats.  If this is what happened, there's a reasonable chance that your PM will have recorded the event in the log and it will turn up at your next interrogation.

Against this, is that this sort of arrhythmia will normally drop your cardiac output quite significantly and you will often feel terrible and be unable to keep exercising at the same level.  You say that you got off the bike and laid down (both good things to do), but didn't feel bad - perhaps because you did the best thing.

As the arrhythmia ended, your monitoring devices could detect normal beats/regular pulse waves so their reported HR suddenly shot up.

You have to ask yourself if you were pushing hard in the spinning class: if yes, then that makes an arrhythmia more likely.  There's no guarantee that your PM will have recorded the episode (they aren't nearly as sensitive for detecting this type of problem as an implanted Reveal device), and a lot depends on the settings selected that control what your PM will record.

Try not to dwell on it, but make sure that you are well hydrated when exercising.  We sweat a *lot* during a hard spinning class.

2:1 block or hit max track rate

by PacedNRunning - 2020-11-23 07:00:25

When you have complete block or any kind of AV block the upper rate limit really matters.  The PM will pace up to your max track rate ie 160bpm. Once you are at 160bpm it will only pace at 160 bpm so if your sinus rate is going at 165bpm, your bottom will only pace at your max of 160bpm.  There is a 2:1 rate that will happen once you go over that but it should be higher than your upper rate limit.  So if your upper rate is 160bpm, your 2:1 block rate should be higher ie 200bpm.  Ask what your upper rate limit is. See if they can adjust it higher to fix the sudden drop. This happened to me as well.  I started at 160bpm as my upper rate and now at 185bpm and rarely get over 175bpm. So your upper rate limit should be a number you can't reach.  If your heart is healthy otherwise, they should be able to adjust your max track higher.  

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