MeanRR

Mean RR interval: average time between heartbeats and its relation to heart rate.

MeanRR — the mean RR (NN) interval — is the average time between two successive heartbeats, measured from the peak of one QRS complex (R wave) to the peak of the next on the electrocardiogram. It is the exact reciprocal of the mean heart rate and the basic quantity from which almost all heart-rate-variability indices are derived.

Heart rate variabilityECGHeart rateTime domain

Healthy adults, 5 min rest926 ± 90 ms

Normal resting range≈ 600–1000 ms

ConversionHR = 60000 / MeanRR

Unitms

What MeanRR shows

The RR interval is the length of one complete cardiac cycle. Its average over a recording reflects the "operating level" of the heart: long intervals mean a slow heart rate (rest, sleep, high vagal tone, good fitness), short intervals a fast one (exercise, stress, fever, sympathetic dominance). Because the ventricles are activated with each QRS complex, MeanRR also describes the ventricular rate. For HRV analysis only normal sinus beats are used (NN intervals); extrasystoles and artefacts are removed.

Figure 1. The RR interval is measured between successive R waves. Mean RR and mean heart rate are two expressions of the same quantity.

MeanRR = Σ NNᵢ / N · HR (bpm) = 60000 / MeanRR (ms)

Interpretation

Healthy adults in short-term recordings average 926 ± 90 ms (Nunan 2010). Children have shorter intervals.
MeanRR, ms	Mean HR, bpm	Interpretation
< 600	> 100	Short — tachycardia: exercise, stress, fever, anaemia, dehydration, hyperthyroidism, heart failure, arrhythmia
600–1000	60–100	Normal at rest
1000–1500	40–60	Long — normal in sleep and trained people; otherwise check for conduction disorders or medication effects
> 1500	< 40	Very long — marked bradycardia; with symptoms needs evaluation

MeanRR is closely linked to other HRV indices: most variability measures (SDNN, RMSSD, Baevsky indices) increase as MeanRR lengthens, partly for purely mathematical reasons. Interpreting HRV therefore always requires knowing the mean heart rate at which it was measured.

When to see a doctor

Consult a doctor if MeanRR at rest is repeatedly shorter than 600 ms (pulse above 100) or longer than 1500 ms (pulse below 40), or if changes are accompanied by palpitations, dizziness, fainting or shortness of breath.

References

Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. Heart rate variability: standards of measurement, physiological interpretation and clinical use. Circulation. 1996;93(5):1043–1065. doi:10.1161/01.CIR.93.5.1043
Nunan D, Sandercock GRH, Brodie DA. A quantitative systematic review of normal values for short-term heart rate variability in healthy adults. Pacing Clin Electrophysiol. 2010;33(11):1407–1417. doi:10.1111/j.1540-8159.2010.02841.x
Fox K, Borer JS, Camm AJ, et al. Resting heart rate in cardiovascular disease. J Am Coll Cardiol. 2007;50(9):823–830. doi:10.1016/j.jacc.2007.04.079

This article is for general information and does not replace a consultation with a doctor.

Published on 24 June 2019