Hi dear colleague,

The heart rate variability is a method that quantifies the difference between successive sinus heart beats. So, the basic asumption of this method is that the individual has a preserved sinus rhythm. Since your subject present some arrhythmias, you will not be able to detect if his heart rate variability is promoted by the autonomic nervous system or by the arrhythmias.

You can try exclude the ectopic heart beats and then interpolate the missing data, before the analysis of HRV. However,  if the amount of such arrhythmias is too large, your analysis will be compromised.

Why don't you try to assess other indexes of autonomic function in your subject ? A simple way would be to quantify the heart rate recovery after a single session of exercise.

I hope my answer can help you. 

Tiago

If you are talking of Respiratory Sinus Arrhythmia, yes.If Non-respiratory or in association with Complete Heart Block, no.

Dear Tiago Peçanha, 

Thank you for your answer. 

I already have the HRVs calculated for all my subjects, and I do not have the option of assessing autonomic function with other methods. Now I need to decide whether HRV in subjects who had sinus arrhythmia (SA) is valid for further analysis...

I was thinking, as other colleagues suggested, that SA is a physiological phenomenon, therefore HRVs measured in those subjects should be valid. Do you think that this is correct and what is your opinion about that?

Thanks again.

Simin

"I need to decide whether HRV in subjects who had sinus arrhythmia (SA) is valid"

"that SA is a physiological phenomenon, therefore HRVs measured in those subjects should be valid."

You've muddied the water here somewhat by saying 'sinus arrhythmia'. From what you've said this could be one of two things:

* I have a 70 year old patient, their HRV is really low, so is it valid to calculate short-term (i.e. respiratory) related changes in their heart beat over time?

* I have a 70 year old patient who has frequent cardiac arrhythmia (APCs/VPCs etc.), so is it valid to calculate their HRV?

What you've written above that I've bolded implies you mean the second option. However, this isn't *sinus* arrhythmia. It's just arrhythmia or dysrhythmia.

If you're not measuring the difference between beats in normal sinus rhythm, you're not measuring HRV. This is why there are so many methods for automatically detecting and removing arrhythmia published - because it needs to be quantified and removed before you perform analysis. 

The easiest way to demonstrate the scale of the problem is to make a 'fake' arrhythmic error and see what happens to your data. 1) find a series of clean RR intervals and analyse it, 2) for two consecutive intervals, make the first one 400ms shorter and the second one 400ms longer, 3) run the analysis again.

Your introduced error should seriously distort many of the typical HRV calculations esp. those over the short-term - simple and straightforward. You can see a similar approach, taken to 24 hour records, here:

http://link.springer.com/article/10.1186%2F1475-925X-11-2

Any subject with persistent arrhythmia should be removed from analysis.

The analysis of respiratory sinus arrhythmia is one of the ways you can use to assess cardiac autonomic modulation of its volunteers or patients. Like any research tool, there are criteria for their use so that data are reliable and that you can interpret the phenomenon you are studying. If your patient has pathological changes in heart rate, they will interfere in their data analysis of respiratory sinus arrhythmia, whose oscillations of RR intervals were due to the way that your patient breathed and that interferes with the power spectral band between 0, 15 to 0.4 Hz. If cardiac stimuli were originated from ectopic heart outbreaks, they will cause bias in their analysis and their data will not reflect the true respiratory sinus arrhythmia. 

This could be solved with the completion of a clinical electrocardiogram and thus you could identify whether or not there are pathological changes in heart rhythm.

Technically speaking, HRV is a frequency modulation

of the sinus node relaxation oscillators(carrier frequency), driven by ANS.

The possibility of demodulation in the presence of the carrier distortions and noise,

has a threshold, below which it is impossible to obtain the modulating signal.

Dear Simin Mahinrad,

I suggest you to read carefully the answers of Dr. Heathers and Dr. Paschoal. I strongly agree with them.

The main question is: What are you referring as "sinus arrhythmia"? From what you've saying, I think that your individuals present non-sinus arrhythmia, eg. premature heart beats,  atrial flutter, etc.  If this is so, you have to remove this irregularities before calculating the heart rate variability. 

The problem here is how many episodes of arrhythmias do your individuals have? If they are very recurrent, so I am afraind that removing them will result in great loss of information. I they are rare, so you can  remove it from your signal and perform the heart rate variability analysis using the standard methods.

There are a lot of methods for removal of such ectopic heart beats. If you have the entire ECG signal you can remove it manually and then you can interpolate the missing heart beats. If you just have the RR-interval time-series (e.g. from a heart rate monitor), there is also some interpolation methods that can be used in order to subsititute the missing data. 

Please, let me know if my answer helps you. If not, I kindly ask you to try to explain better your case. Maybe you could do some prints of your signal and upload here so we can try to give you some directions.  

Best,

Tiago

Dear Simin,

unfortunately the term "arrhythmia" is ambiguous:

So for your problem it is important to clarify if the "arrhythmia" should be classified as a physiological or a pathological one (which, I must confess, is not always easy).

Kind regards, Matthias

Dear Tiago, 

Thank you very much for your answer and I understand what the problem is now. 

i need to contact the person who calculated the HRVs.. 

Regards,

Simin

Dear all,

Thank you so much for your explanations. It was a huge help for me in understanding and solving the problem.

Best,

Simin

Dear Tiago

Frequency based HRV measures are likely to be polluted to use but Poincaré analysis may be suitable

Regards, Michael

Hi, Respiratory Sinus Arrhythmia is normal health signal and appears on everybody heart rate. An important thing is that a subject has heart rate recovery.