<p>The difference is rather simple. NN-intervals refer to the intervals between <strong>normal</strong> R-peaks. During a measurement, artifacts may arise due to arrhythmic events or faulty sensors, for example (<a href="https://www.researchgate.net/publication/230638325_A_Real-Time_Automated_Point-Process_Method_for_the_Detection_and_Correction_of_Erroneous_and_Ectopic_Heartbeats" rel="noreferrer">Citi, Brown &amp; Barbieri, 2012</a>). This may lead to abnormal R-peaks, which may in turn distort the statistical measures. To ensure reliable and valid data, only normal R-peaks are selected. Alternatively, the abnormal R-peaks can be corrected. </p>

<p>In practice, however, RR-intervals and NN-intervals are synonymous (Tarvainen, 2014; <a href="https://en.wikipedia.org/wiki/Heart_rate_variability" rel="noreferrer">Wiki</a>). The use of "NN-intervals" is merely used to emphasize that normal R-peaks were used. </p>

<hr>

<h3>References</h3>

<p><a href="https://www.researchgate.net/publication/230638325_A_Real-Time_Automated_Point-Process_Method_for_the_Detection_and_Correction_of_Erroneous_and_Ectopic_Heartbeats" rel="noreferrer">Citi, L., Brown, E. N., &amp; Barbieri, R. (2012). A real-time automated point-process method for the detection and correction of erroneous and ectopic heartbeats. IEEE transactions on biomedical engineering, 59(10), 2828-2837.</a></p>

<p>Tarvainen, M.P. (2014). Kubios HRV version 2.2: User's Guide. </p>

<p><a href="https://en.wikipedia.org/wiki/Heart_rate_variability" rel="noreferrer">https://en.wikipedia.org/wiki/Heart_rate_variability</a></p>

CC BY-SA 3.0
2016-10-17T14:02:01.113Z
2016-10-28T09:43:56.837Z
2016-10-28T09:43:56.837Z
Robin Kramer-ten Have
<p>Heart rate variability (HRV) is often used as a measure of the sympathetic nervous system. One way to quantify HRV is by calculating the Inter-beat interval (IBI), also referred to as the RR-interval. The RR-interval refers to the time between two R-peak of a traditional ECG heart-beat waveform (see Figure 1). </p>

<p><a href="https://i.sstatic.net/B4j77.png" rel="noreferrer"><img src="https://i.sstatic.net/B4j77.png" alt=""></a><br>
<em>Figure 1: Two subsequent heart-beats with component names. The RR interval is the time between two subsequent R-peaks. Picture taken from: <a href="http://lifeinthefastlane.com/ecg-st-segment-evaluation/" rel="noreferrer">http://lifeinthefastlane.com/ecg-st-segment-evaluation/</a></em> </p>

<p>However, in a review article by <a href="http://journal.frontiersin.org/article/10.3389/fpsyg.2014.01040" rel="noreferrer">Shaffer, McCraty and Zerr (2014)</a> they refer to normal-to-normal (NN) intervals instead. This extends to the statistical measures of the RR intervals, such as SDRR, pRR50 (<a href="http://innovareacademics.in/journals/index.php/ijcpr/article/viewFile/3396/1314" rel="noreferrer">Urooj, Gupta, Sp &amp; Tandon, 2014</a>), i.e., SDNN and pNN50, respectively (Shafer et al., 2014). 
<strong>What is the difference between RR-intervals and the NN-intervals?</strong></p>

<hr>

<h3>References</h3>

<p><a href="http://journal.frontiersin.org/article/10.3389/fpsyg.2014.01040" rel="noreferrer">Shaffer, F., McCraty, R., &amp; Zerr, C. L. (2014). A healthy heart is not a metronome: an integrative review of the heart's anatomy and heart rate variability. Frontiers in psychology, 5, 1040.</a>  </p>

<p><a href="http://innovareacademics.in/journals/index.php/ijcpr/article/viewFile/3396/1314" rel="noreferrer">Urooj, M., Gupta, S., Sp, V., &amp; Tandon, M. (2014). REFERENCE RANGE OF HEART RATE VARIABILITY AND VALIDATION IN SUBJECTS WITH ASYMPTOMATIC ELEVATED LIVER FUNCTION ENZYMES. International Journal of Current Pharmaceutical Research, 6(4), 49-52.</a>  </p>

<methodology><data><workload><heart-rate-variability><ecg>
What is the difference between RR-intervals and NN-intervals in HRV-data?
Robin Kramer-ten Have
# What is the difference between RR-intervals and NN-intervals in HRV-data?

(Asked by: username_0 on 2016-10-17)

Heart rate variability (HRV) is often used as a measure of the sympathetic nervous system. One way to quantify HRV is by calculating the Inter-beat interval (IBI), also referred to as the RR-interval. The RR-interval refers to the time between two R-peak of a traditional ECG heart-beat waveform (see Figure 1).

[![](https://i.sstatic.net/B4j77.png)](https://i.sstatic.net/B4j77.png)  
*Figure 1: Two subsequent heart-beats with component names. The RR interval is the time between two subsequent R-peaks. Picture taken from: <http://lifeinthefastlane.com/ecg-st-segment-evaluation/>*

However, in a review article by [Shaffer, McCraty and Zerr (2014)](http://journal.frontiersin.org/article/10.3389/fpsyg.2014.01040) they refer to normal-to-normal (NN) intervals instead. This extends to the statistical measures of the RR intervals, such as SDRR, pRR50 ([Urooj, Gupta, Sp & Tandon, 2014](http://innovareacademics.in/journals/index.php/ijcpr/article/viewFile/3396/1314)), i.e., SDNN and pNN50, respectively (Shafer et al., 2014).
**What is the difference between RR-intervals and the NN-intervals?**

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### References

[Shaffer, F., McCraty, R., & Zerr, C. L. (2014). A healthy heart is not a metronome: an integrative review of the heart's anatomy and heart rate variability. Frontiers in psychology, 5, 1040.](http://journal.frontiersin.org/article/10.3389/fpsyg.2014.01040)

[Urooj, M., Gupta, S., Sp, V., & Tandon, M. (2014). REFERENCE RANGE OF HEART RATE VARIABILITY AND VALIDATION IN SUBJECTS WITH ASYMPTOMATIC ELEVATED LIVER FUNCTION ENZYMES. International Journal of Current Pharmaceutical Research, 6(4), 49-52.](http://innovareacademics.in/journals/index.php/ijcpr/article/viewFile/3396/1314)

**Tags:** methodology, data, workload, heart-rate-variability, ecg


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## 1 answers

### Answer by username_0 on 2016-10-17. Score: 5 | Accepted answer

The difference is rather simple. NN-intervals refer to the intervals between **normal** R-peaks. During a measurement, artifacts may arise due to arrhythmic events or faulty sensors, for example ([Citi, Brown & Barbieri, 2012](https://www.researchgate.net/publication/230638325_A_Real-Time_Automated_Point-Process_Method_for_the_Detection_and_Correction_of_Erroneous_and_Ectopic_Heartbeats)). This may lead to abnormal R-peaks, which may in turn distort the statistical measures. To ensure reliable and valid data, only normal R-peaks are selected. Alternatively, the abnormal R-peaks can be corrected.

In practice, however, RR-intervals and NN-intervals are synonymous (Tarvainen, 2014; [Wiki](https://en.wikipedia.org/wiki/Heart_rate_variability)). The use of "NN-intervals" is merely used to emphasize that normal R-peaks were used.

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### References

[Citi, L., Brown, E. N., & Barbieri, R. (2012). A real-time automated point-process method for the detection and correction of erroneous and ectopic heartbeats. IEEE transactions on biomedical engineering, 59(10), 2828-2837.](https://www.researchgate.net/publication/230638325_A_Real-Time_Automated_Point-Process_Method_for_the_Detection_and_Correction_of_Erroneous_and_Ectopic_Heartbeats)

Tarvainen, M.P. (2014). Kubios HRV version 2.2: User's Guide.

<https://en.wikipedia.org/wiki/Heart_rate_variability>


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