Pacemaker and Heart Rate Variability

I have a three year old St. Jude Pacemaker for Bradycardia which maintains my  heart rate at 60(does go down to 55 sometimes at night).  Six months ago I got an Apple Watch to record my exercise results.  It also records Heart Rate Variability and my numbers are quite low(6-9) with an occaisional spike to 30-55 lasting for 1-2 days.  My research comes up empty regarding the question: Can an implanted Pacemaker effect HRV?  My cardiology opined it was possible but wasn't sure and wasn't familiar with any research supporting his speculation. Help/


PM and HRV

by ar_vin - 2021-07-15 18:55:36

If you think about it a little you'll understand that for atrial pacing (as in the case of bradycardia) HRV can be quite meaningless. The synthetic pacing rates do not have a programmed variability; the normally functioning sinus node responds to a range of inputs to synthesize a pacing rate which might result in a variable heart rate. Higher heart rate variability is claimed to be associated with better recovery from exercise and other stressors in a normally functioning sinus node. With a "sick sinus node" (which is the primary cause of bradycardia) I doubt HRV measurements would provide any meaningful information.

There have been research  efforts to create a pacemaker that might mimic the "natural" sinus node but none that are in commercially available PMs AFAIK. I would love to know if there's such a PM on the market.




Heart rate monitors

by AgentX86 - 2021-07-15 22:10:44

I think ar_vin has it right, as far as heart rate variabiity.  All you're doing is measuring the response of the pacemaker, which, of course, has nothing to do with your conditioning.

Add to that, heart rate monitors are iffy, or worse, for people without pacemakers.  Pacemakers make things more complicated, particularly the EKG type (which I think the Apple Watch is).  They work for some and not at all for others.The Pulse-ox sort of watches are much worse, but for everyone.  Watches slide around, making it almost impossible for the sensor to stay on the artery without a lot of variation in the signal.  It's hard enough to get them to work when you're still.  You really can't rely on a watch to give any reliable numbers.  Take your pulse manually.

I would say your cardiologist is dreaming.  The sinus node measures the pCO2 of the blood and increases heart rate as pCO2 increases.  Muscle energy requires H and O2 to "burn" ,which creates CO2).  There is a 1:1 corelation between O2 and C02, so the heart has the measurement it needs to pump the oxygen-rich blood required blood to fuel the body for the work being done.  Work more => higher CO2 concentration => heart pumps faster.  Pacemakers don't have access to blood so can't measure the pCO2.  If it were possible to measure pCO2 the pacemaker would need a chemical lab.  How do these chemicals get stored/replentished?

Current pacemakers try to calculate the needed heart rates indirectly by motion or, in some cases, by measuring the breathing rate.  Neither of these work well in every case and are difficult to tune.  This indirect approach may get better but I don't see a direct measure in any of our lifetimes.



HRV: cause or effect?

by crustyg - 2021-07-16 10:05:07

I think the fundamental problem with HRV as an indicator of better outcome is that it's difficult to see how anyone can tease out cause and effect.

It seems to me just as likely that those who go into an illness with significant HRV are just more healthy to start with than those with little HRV, so it would make perfect sense to expect a better outcome for those that start in better shape.  It's very close to University-of-the-Bleeding-Obvious.  Overweight folk do less well than healthy, non-overweight people, and despite all of the on-message noise to the contrary, lack of exercise is the number 1 cause of people being overweight (no flame wars, please, it's not the *only* cause).  And HRV is most pronounced in those with a healthy, fairly athletic heart with good blood vessels and decent lungs, because most of HRV is actually sinus-arrhythmia.  I've posted elsewhere that any idea that introducing artificial HRV into a bradycardia-PM might be better for you is a) probably complete nonsense, b) unlikely to get regulatory approval.

I think you're sweating the wrong detail.  There are much better heart-related numbers to focus on than HRV.

Pacemaker and Heart Rate Variability

by mac1coffey - 2021-07-16 12:41:17

I really appreciate your detailed responses.  Looking back on my appointment I believe my cardiologist was attempting to say the same thing in a complicated 3  minute tutorial. I beleive I should stop looking at my Apple watch HRV..  My blood panel numbers and weight are excellent, eat right and exercise x3 weekly and enjoy a 50 year marriage. Thanks.  


by islandgirl - 2021-07-17 00:01:14

Coincidentally, I saw my EP this past week and HRV came up.  I'm in a pilot study for people that survived a SCA.  HRV is measured.  He showed on the ICD Medtronic computer screen I had no HRV due to sinus node dysfunction.  I always learn more on this site.  Great question and thanks to all that responded.

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