Reduced heart rate variability predicts fatigue severity in individuals with CFS/ME. Escorihuela et al. 2019

I agree, HRV is too non-specific to be a useful predictor.

 

Given that HRV is affected by just about any stressor on the body, whether physical, psychological or environmental, I can see it has biomarker potential for showing the body struggling with something or other - but they don't seem to have found any ME-specific HRV signature (or have they? details were a bit over my head) so I can't see how HRV would be a useful part of any diagnostic criteria.

The bit about using HRV as an end-point marker in treatment trials could be worth looking at further though. I have a dim memory reading about just that being done in heart failure. If your HRV improves it means you're objectively getting better, and vice versa. And they do show here that HRV and the severity of certain symptoms correlate, which is also what many patients have found with their own monitoring. If reliable readings can be taken that would be better than a lot of the questionnaires we usually get.

 

I agree with @Michiel Tack and @Snow Leopard and @Ravn

It is very likely that HRV is a non-specific ME marker but nevertheless it can help us to identify potentially interesting mechanisms behind ME.

 

Escorihuela et al 2020 found reduced HF and LF in patients (and LF/HF ratio), compared to the case-controls, and inappropriately concluded this is due to "increased sympathetic hyperactivity". It is notable that they simply stated that participants had "natural breathing", without providing any measurements or evidence of respiratory rates, which can have a substantial impact on HRV...

If both LF and HF are reduced then the more likely cause for the findings is different respiration rates and reduced vagal/parasympathetic drive (and deconditioning is a big factor). If it was primarily due to "increased sympathetic hyperactivity" then the increase in LF/HF ratio would be due to an increase in LF power, not a decrease in both LF and HF.

Of course it is not that simple!


Counter with:
"An Overview of Heart Rate Variability Metrics and Norms"
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5624990/

It is always important not to confuse the directionality between cause and effect when measuring correlations. Many biological changes hypothesised as being the cause of an illness, may in fact be adaptations, either positive or negative. In this case, different activity patterns and lower fitness could result from more severe illness, which on its own (less intense activity patterns and lower fitness) has been shown to cause the aforementioned HRV findings in healthy participants.