Heart Rate Variability

I went for a bike ride this evening and pushed my heart rate up to 145 BPM going up a hill.  In less than 3 minutes I was on the bottom of the hill and my rate dropped to 52 BPM.  During the entire ride leading up to the drop I was averaging 105 to 110 BPM.  Anybody else encounter pacemaker issues when first excersing?


Not enough information

by AgentX86 - 2019-12-02 22:29:22

Why do you have a PM?  Are you chronotropically incompetent? How are you measuring your HR?  A lot more information is needed before anyone can even guess.

Heart Rate Variability

by jamfer - 2019-12-02 22:54:22

Additional information:  I'm 42 and just got a pacemaker 1 month ago for complete heart block.  Lower chambers are being paced about 55% of the time.  I have an Apple Watch 5 giving me the heart rate.  After the sudden heart rate drop I took my pulse manually as well.  Counted the beats for 15 seconds and multiplied by 4. 

I’m pretty new ...

by Pacer2019 - 2019-12-03 01:43:44

My PM is set at 60 on the bottom and I understand it won’t let my heart go below . 

I have heart block and a single chamber device . 

Here is my situation : 

I am active and I’m up to full speed now - inserted 10/23.

i play competive racquetball which demands plenty of oxygen .... I notice I get winded which  and didn’t used to .   

My EP has said my device needs to be adjusted given my activity level - I’m going in 12/11 for them to check it out and possibly adjust . 

Maybe you should call E.P. and share your story ? 

Why is HR variability a problem?

by crustyg - 2019-12-03 03:28:09

Your PM has been designed to pace you at a rate that attempts to match your need for increased cardiac output, and clearly you have Rate Response enabled.  Your model of PM has an accelerometer fitted (same as in a smartphone that allows it to work out which way is down) and it uses the data from that to detect your chest movements and that drives a software algorithm that increases your HR.

As you work hard pedalling to go up hill your PM will increase your HR, and when you relax and freewheel down the other side, your HR will reduce.  Various forms of cycling will produce more or less accelerometer signal and your PM has response factors that can be adjusted for the movement needed to drive the software to deliver max HR.  These factors can be tuned to suit you.

At your age, a suitable maxHR is probably more than 145bpm, and if your heart is fit then a lower HR of 52 is reasonable.

What really matters is how you *feel* - can your legs manage the hills, do you get chest pain at 145bpm, are you feeling faint or dizzy at 52bpm?


by MrTech - 2019-12-03 05:03:45

Why is RR on if you have an implant for CHB? 

I keep hearing that people have RR on for CHB. I’d be interested in the rational for this if there is no chronotropic incompetence. 

The only potential issue is you hitting your max tracking rate but I would guess it would be higher what your HR got to during exercise anyway. Given your age I’d imagine it would have been set higher than 120bpm. 

Rate response for CHB - rationale

by crustyg - 2019-12-03 07:46:31

I hope I'm not missing something vital here, but I'll contribute anyway.

For most people, the natural rate response of the heart to exercise is driven by the SA node.  Yes, you do see an increased rate if you're on a junctional nodal drive only (as I was, my SA node is silent), *BUT* you don't see anything like enough of an increase purely from that.

Tracking the atrial impulses and then generating a delayed but matching ventricular pulse only works up to a certain rate, as the PM *must* wait some time before generating the vent pulse a) to allow for atrial contraction to provide adequate ventricular filling (which is vital for a decent cardiac output) and b) because it's essential that the PM doesn't generate a pulse that nearly coincides with any junctional/nodal natural impulse to avoid triggering VF.  Trouble is, as the required rate increases the programmed delays start to occupy too much of each second and the A-then-V tracking mode runs out of room/reaches max rate.  It's commonly around 130bpm.  But that's not good enough for a lot of athletic folk, so the PM may have a mode switch enabled where it will just drive the ventricles in a less synchronous mode to achieve a higher HR (and hopefully, greater cardiac output).  It will watch for each vent impulse, and then generate the next pulse, safely, but soon to achieve a higher maxHR, using the RR feature.

Effectively, everyone with CHB has a degree of chronotropic incompetence, which is why they all end up with a PM, some later than was perhaps ideal.  The sympathetic nerve supply to the heart does affect both SA node and AV node, but the AV node just doesn't have cells with a high enough response to deliver a good maxHR.  Does that make sense?


by MrTech - 2019-12-03 13:03:41

‘Everyone with CHB has a degree of chronotopic incompence’. Not to sound contrary but I’ve never seen that documented anywhere or , In fact, try and find research suggesting SInus node disease and AV node diseas are linked. Papers suggest the opposite (on limited info out there - congenital CHB is different). The fact they both are connected to the sympathetic nerve doesn’t mean they both get effected.  There are many many reasons why diseases’ of each SA node or AV node can separately occur. 

People with SSS can have a perfectly functioning AV node and visa-Versa. 

Hitting a 2:1 HB due to AV delays in someone with CHB isn’t going to improve with RR on.  You don’t turn on RR to try stop that. 

If your own sinus rate can reach say 150bpm on its own and you find your are suddenly getting 2:1 HB (assuming one has CHB)?  RR is going to nothing to help. Regardless whether you begin with a atrial senses or atrial paced beat, the AV delay determines the ability to allow the V rate to keep up. 

You turn on RR if you have a blunted response to exertion.

People with CHB can have a perfectly functioning SA node and one shouldn’t assume RR is needed.  

Anyway it really isn’t the end of the world if it’s on. Just might not be needed. If it was me I’d let my own body determine its HR variation before turning RR on. 

Of course - it’s the doctors decision etc etc. 

Not making sense

by crustyg - 2019-12-04 13:31:15

I'm sorry if I'm not explaining myself very well.

MrTech: No-one - and certainly not me - is suggesting that SA node and AV node disease are necessarily linked (although ischaemic heart disease can do it). My point, which clearly I'm not getting across, is that the main source of an increased heart rate is the SA node: if you have CHB, then how does the increased rate from the SA node reach the ventricles to achieve a greater ventricular rate - and hence greater cardiac output?

My comments about sympathetic nerve innnervation were designed to head off anyone who knows enough cardiology who might say 'Ah, but patients with CHB who survive on a junctional (==AV) rhythm *can* increase their ventricular rate.  True, but not by very much.  You can see the effect of sympathetic innervation of the AV node in patients in AFlut: they often sit at 5:1 block, but as they exercise or become agitated their block reduces to 4:1 then 3:1 and if they are unlucky sometimes to 2:1 or 1:1 - which is sudden cardiac death territory - the atria are typically fluttering at 200-250bpm.

So I stand by my assertion that all patients with CHB have a degree of chronotropic incompetence.  And in my medical experience, *ALL* CHB patients have a 'blunted response to exertion'.

CHB stands for complete heart block. So you don't get 2:1 HB with CHB which your post mentioned.


by MrTech - 2019-12-06 12:46:19

no I’m sorry but I stand by my assertion that -  just because one has CHB, it doesn’t mean ONCE the CHB has been fixed by the pacemaker you you still need RR. 

By all means, please link the data that shows those with AV node disease will also have SInus node disease. 

All your examples are relating to when people are in CHB or in flutter. Not relevant once CHB has been fixed. 

So, once you have 1:1 conduction with aid of a pacemaker, no reason AT ALL to assume you need RR on. 

Also I never said 2:1 was CHB. They are separate things.  i was making the point you can get both as they flip from to the other. 

In summary. IMO (15 yrs In cardiology working directly with devices) slapping on RR straight away without evidence isn’t the best idea.


2:1 Issue

by jamfer - 2020-01-19 12:45:34

I had a different pacemaker tech look at my settings and issue with my heart rate crashing when exercising.  He immediately recognized the issue.  My lower rate was set to 50 bpm and my upper rate was set to 130 bpm.  My lower chambers are 100% paced.  When my heart rate went over the 130 bpm the lower chambers reset to 50 bpm.  I'm not sure of the specifics but he said it was a 2 for 1 beat or something.  He increased my upper rate to 160 bpm and I haven't had the issue since.  

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