Pacemaker – Lower Rate/Upper Rate what does this really mean?
A pacemaker does not LOWER your heart rate it stops it going too low. In essence if your lower rate is set to 60 your heart will not drop below 60bpm.
The 130 is a little harder to explain but bear with me…
Now we all have a natural pacemaker in our heart called the Sino Atrial Node in healthy hearts our Sino Atrial node makes our heart go quicker when we are exercising… If you run up a hill your heart rate increases.
Now in some hearts that require pacemakers the signal from the top of the heart doesn’t reach the bottom of the heart (Heart Block).
Lets take a scenario where a man has complete heart block and NO pacemaker (the signals from the top of his heart doesn’t reach the bottom of his heart).
This man is asleep and his NATURAL pacemaker is going at 60 bpm…. but the bottom heart (ventricles) aren’t getting this signal (because of the heart block). So instead they contract at 30 bpm as a safety mechanism.
This person may feel faint or tired because the top of his heart, which doesnt do much in terms of pumping blood to the whole body are going at 60 but his bottom part (which does most of the hard work supplying the body) is going at 30.
Enter a Pacemaker, this gentleman gets a pacemaker, he has a lead in the top heart and a lead in the bottom heart. This allows communication between the two!
Now this gentleman is asleep his top heart is going at 60bpm again but this time the pacemaker can recognise this and pace the bottom chambers accordingly. Now he has an upper chamber heart rate of 60 bpm and a bottom (paced) heart rate of 60 bpm.
This is great because this persons natural pacemaker is still working well and is being used by the pacemaker to know what rate to pace the bottom chambers of the heart.
This gentleman runs up a hill…. his natural pacemaker in the top of his heart increases to 115bpm…. the pacemaker recognises this and makes the bottom chambers beat at the same rate. The top and bottom are now both going in synchrony at 115bpm.
This is all working well…. and will in this case work all the way up to the top number 130bpm…. so if he ran up a hill and his top heart was going 130 bpm the pacemaker would pace the bottom of your heart up to 130bpm also…..
BUT in this case 130 is the upper limit for this…. if the top heart was to go any faster the bottom heart would be paced no faster than 130 bpm….. the pacemaker would not track the heart rate in the top of the heart over 130.
There is a simple and good reason for this…..
If the top of your heart went into an arrhythmia like atrial fibrillation, the top of the heart could be going at anything upto 300bpm… if the pacemaker made the bottom of a persons heart go at 300bpm they would be in big trouble! so they dont.
The Upper rate limit 130 is basically saying that the persons heart is likely to go up to that rate in a natural physiological manor… however anything above this should probably be ignored as it may be pathophysiological i.e. something not normal which should be ignored.
Younger people therefore tend to have a larger upper limit i.e 60/180 as there heart can naturally go faster through exercise.
A complete explanation of these topics and more is available in the book Pacemakers Made Easy by Carl Robinson.