Lower limits of PM

Can anyone offer an answer to this question??

My pacemaker is set to prevent my HR from going below 60 BPM

I was diagnosed with SSS along with bradycardia.

So does this mean that my PM only kicks in when my HR wants to drop below 60BPM?? When my heart rate is above 60 BPM is my PM just monitoring and not actually helping my heart beat??

My cardiologist said that my PM is simply acting like an insurance policy. Is this kind of what he meant. l


Thank you!


Yes, sort of.

by crustyg - 2021-05-17 03:18:18

Actually your PM doesn't measure BPM (which implies that it measures beats across a minute at a time).  What it does it watch for activations, and if it doesn't see one for 1000milliseconds (in your case), it delivers an activation.

Think about it: you *could* have 59 beats in 30s, and then nothing for another 30s.  Your BP would crash and so would you.  Waiting until a full minute has elapsed before delivering the 60th beat wouldn't be useful.

Therefore, you *may* find your PM pacing at 1-2% even though you *think* your natural rate is already at 60BPM.

Make sense?

Lower limits of pacemaker

by Gemita - 2021-05-17 06:42:36

Steve, Hope you are doing well.  Yes I believe you are correct in saying your pacemaker is simply there to protect you when you need protection (like an insurance policy) and that the pacemaker will only step in when your heart rate falls below your personal set minimum (60 bpm) or when you need support during any electrical disturbances with your Sick Sinus Syndrome. 

I just wanted to say however that it can be perfectly normal for our pacemakers to register a bpm slightly below our minimum set level.  Mine does this quite often.  My set minimum is 70 bpm and I can see my rates are regularly in the range 67-69 bpm, particularly in the presence of arrhythmias.  I found crustyg's explanation very helpful

Chronotropic Incompetence- Rate Response?

by Marybird - 2021-05-17 10:41:54

SteveV, though you don't mention this in your post, the inability of the heart to beat fast enough to keep up with the person's activity levels, or chronotropic incompetence, (CI)  is often part of the sick sinus syndrome package. The rate response program on the pacemaker can be activated so the pacemaker can kick in to provide a heart rate that will go up when you need it to during increased activity.

It may be, if your EP didn't mention it to you, you don't have issues with CI, and your rate response setting is off. With CI, you'd notice perhaps shortness of breath, tiredness, and difficulty completing activities, like walking up lots of steps, exercise, or heavy work, as your heart rate would not increase enough to provide you with the " oomph" you need during those activities. With the pacemaker's rate response turned on, your heart rate would increase to levels where you can function better during those activities. 

I also have sick sinus syndrome- tachy- brady, and went about 6 weeks after the pacemaker implant with the lower heart rate set at 60, and rate response turned off. I felt better, but still had some problems with increased activity, like exercise and even trying to walk fast, stairs. Even with all that they found my atrial pacing rate was 84%.

At my 6 week post- implant checkup the EP turned on the rate response, and reset the lower heart rate setting to 55. He told me this would save a little pacing when I slept, with no need during sleep to pace to 60. He also said I wouldn't see my heart rate at 55 much as the rate response would keep it higher with any activity at all. That's proven to be the case, and that rate response has made the biggest difference, I feel so much better. And with the rate response on, my atrial pacing rate has increased to the low 90- something percentages. 


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