upper limit

Can someone please explain the "upper limit" that I sometimes read about on these pages!
I understand(i think) the lower limit,where if your heart beats less than a certain number of beats per minute the P.M sends an electrical charge to make it contract and beat, but don't understand how your heart rate can be slowed by a p.m!

4 Comments

gobsmacked!

by sputnick - 2009-02-11 02:02:14

I had no idea it was so complicated and clever a device. I knew it gave out an electrical impulse, but didn't know that the wires also carried info FROM the heart back to the p.m. I'm learning all the time and will get more info on what excactly I have when I go for my 1st checkup, although I do know that I have a dual-chamber p.m.
You are all such a BIG help. Thanx
Janx

P.S. I have printed this out then I can refer to it when needs be.

you're right

by Angelie - 2009-02-11 02:02:49

It doesn't slow a fast heart at all.
A pacemaker "fires" when someone's natural rate goes lower than the set low rate.
There still is a high rate, mainly for EGM recordings, but the pacemaker does not slow a fast rate down.
Only a defibrillator can shock a rhythm back down.

Technical Details

by tuck3lin - 2009-02-11 04:02:55

If you REALLY want to know the details, I found the following technical paper called "The Evolution of Pacemakers" on the Institute of Electronic and Electrical Engineers (IEEE) web site:

http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=01636350

Circuit diagrams and everything. There is enough non-technical information that most PM recipients will get something out of it, even if they aren't an electrical engineer.

Upper limit

by E from Spain - 2009-02-12 09:02:43

As you said, many PM are used to avoid low HR. But many times the PM is necessary to keep the heart beating the whole time.

I have a complete AV block. Thus, there is no connection between the upper part of the heart and the lower. The PM detects the normal pulse in the right atrium and sends a pulse to the right ventricle. In my case I have my upper limit at 180 beats per minute. If my demand is 180 or less the system works normal. The limitation starts when my demand is higher than 180. In that case, my atrium can beat faster than 180 but the PM is skipping same beats and sending a maximum of 180 pulses to the ventricle.

The question now is; why there is an upper limit? Sometimes it is necessary to control the upper rhythm because the heart is not too healthy, or because the person carrying the PM is too old. There are many other reasons.

A part of the upper limit that can be adjusted, there is the limitation of the device. Depending on the PM model, there are different limits. In my case, the PM can not “read faster” than 210-220 beats per minute. That means that when my right atrium beats faster than 220, the PM can not read all the beats because it needs some milliseconds to transmit the signal from the atrium and, therefore the PM can miss some beats.

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A pacemaker suddenly quitting is no more likely to happen than you are to be struck by lightening.