Heart rate dropping at night

This is (I hope) more curoiosity than anthing else... but whatever. There are some heart rhythm experts here that I hope can provide insight.

Background: after years of adventures with drug resistant AF, pace-and-ablate, then diagnosed with diastolic heart failure (should have been diagnosed10 years before but hey), having an SCA and then an ICD, I had a heart transplant in 2022.  Life was (and continues to be) good (we wil not dwell on drug side effects because honestly they're minor in the scheme of things I endured in the past).

However, post transplant my resting heart rate was consistently circa 103. Not unusual -- a transplanted heart is not attached to the nervous system and makes up its own mind on when it's going to beat.

18 months after transplant I started having dizzy spells. Identified via 48 hour monitor as 'Intermittent high grade heart block with ventricular standstiills'. (The transplant process unfortunately can damage donor hearts). Cue new pacemaker at zero notice -- just as well I was clued up in advance.

Pacemaker is set so that ventricles follow atria after a short delay, with a minimum of 60 bpm.

So...According to that very accurate Fitbit thingy (tongue very firmly in cheek) my heartbeat drops once I go to sleep to circa 75-85 overnight and then raises to 130ish as soon as I get up. It varies around 120--140 during the day -- very volaitile; not correled with exertion -- but I'm not bothered about that.

However, I do wonder about the heart rate doppong at night. Fitbit rubbish, but it's awfully consisent? Last time i saw my transplant team I asked and they said 'yes, we noticed when you were an inpatient - which rules out the Fitbit)  but dunno' but she was a trainee..

Thoughts?

2 Comments

You are a challenge but a nice one

by Gemita - 2024-05-28 19:39:22

Atiras, I wonder if this could be related to circadian rhythms of heart rate and blood pressure?  There are clearly dippers and non dippers of nocturnal heart rate following heart transplantation?  The second link even suggests Cardiac transplant patients with autonomic denervation have a preserved nocturnal bradycardia 7–36 months after transplantation.  These results challenge the commonly held notion that autonomic tone is the dominant mechanism by which the SCN (Suprachiasmatic nucleus - the brain's circadian clock) drives circadian changes in heart rate.  

I appreciate a fall in heart rate to 75-85 bpm isn't bradycardia (a heart rate below 60 bpm) but since you are consistently lower at night than during the day when I see your heart rate becomes volatile and runs at between 120-140 bpm, this might explain what is going on?  It would appear cardiac transplant recipients still have a circadian rhythm in heart rate. 

Cannot offer any other explanation unless a pacemaker setting or a medication is at work at night lowering your heart rate?  A lower resting heart rate will be safer for you in any event to give your heart a rest from daily tachycardia which might be taking a toll.  

Please do report back when you get confirmation from your medical team that all is functioning as it should.  Remain well.  You are an inspiration to us all

https://pubmed.ncbi.nlm.nih.gov/1386753/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6520649/

Interesting articles

by atiras - 2024-05-29 15:57:10

Thank you, Gemita. Food for thought. There's a graph in the second article that looks very familiar.

You know you're wired when...

Your ICD has a better memory than you.

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I, too, am feeling tons better since my implant.