MaxRR

Maximum RR interval: longest beat-to-beat interval, vagal slowing and pauses.

MaxRR — the maximum RR interval — is the longest time between two successive normal heartbeats during the recording. It corresponds to the lowest instantaneous heart rate and shows how strongly the heart was slowed by the vagus nerve — typically during exhalation, rest or sleep. Very long intervals may also reveal sinus pauses or conduction blocks.

Heart rate variabilityECGBradycardiaPauses

Definitionlongest NN interval

Instantaneous min HR60000 / MaxRR

1000 ms= 60 bpm

Pause on ECGRR > 2000 ms

What MaxRR shows

The vagus nerve can slow the heart within a single beat. With every exhalation, and during relaxation or sleep, the interval between beats lengthens; the longest such interval in a recording is MaxRR. The difference between MaxRR and MinRR — the variation range ΔX — is a simple measure of how widely the vagus modulates the rhythm and is used in Baevsky's indices (AR, AB, stress index).

On standard ECG paper (25 mm/s) five large squares between two R waves correspond to 1000 ms, or 60 bpm.

Figure 1. Converting RR intervals to heart rate on an ECG grid: five large squares (1000 ms) correspond to 60 bpm.

Interpretation

Pauses during sleep in healthy young people and athletes can be benign; the clinical meaning depends on symptoms and the ECG.
MaxRR in a resting recording	Meaning
Up to ≈ 1200–1300 ms	Usual — normal vagal slowing at rest, especially during exhalation
1300–2000 ms	Long — strong vagal tone (athletes, sleep) or the effect of beta-blockers and other heart-slowing medicines
> 2000 ms	Pause — sinus arrest, sinoatrial or atrioventricular block, or a missed beat by the detector; requires ECG review
≥ 3000 ms while awake	Significant pause — especially with dizziness or fainting, needs cardiological evaluation

A single very long interval may also follow an extrasystole (compensatory pause) or be an artefact — such intervals are excluded from HRV analysis.
The ratio of the longest to the shortest interval during deep breathing (the expiration/inspiration ratio) is used in autonomic function tests; a reduced ratio suggests vagal dysfunction, for example in diabetic neuropathy.

When to see a doctor

Seek medical advice if long pauses are found, or if a slow heart rate is accompanied by dizziness, fainting, unusual tiredness, shortness of breath or confusion.

References

Kusumoto FM, Schoenfeld MH, Barrett C, et al. 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay. Circulation. 2019;140(8):e382–e482. doi:10.1161/CIR.0000000000000628
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
Baevsky RM, Chernikova AG. Heart rate variability analysis: physiological foundations and main methods. Cardiometry. 2017;(10):66–76.

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

Published on 24 June 2019