MARI
MARI — the mean absolute RR-interval difference — is a time-domain heart-rate-variability index: the average of the absolute differences between successive heartbeat intervals. It measures how much, on average, each heartbeat differs from the previous one and therefore reflects fast, beat-to-beat (vagal) regulation of the heart.
What MARI shows
The interval between two heartbeats changes with every breath: it shortens when we breathe in and lengthens when we breathe out (respiratory sinus arrhythmia). These quick changes are produced almost entirely by the vagus nerve, whose action on the sinus node starts and stops within one heartbeat. Indices based on successive differences — RMSSD, pNN50, SD1 and MARI — therefore reflect parasympathetic activity, and they are much less affected by slow trends in heart rate than SDNN.
MARI is closely related to RMSSD, the root mean square of successive differences. RMSSD squares the differences, so a few large jumps (artefacts, extrasystoles) influence it strongly; MARI uses absolute values and is somewhat more robust. For normally distributed differences MARI ≈ 0.8 × RMSSD.
Reference values and interpretation
There are no separate international norms for MARI. Its values can be estimated from RMSSD: in short-term (5-minute) recordings healthy adults have RMSSD of about 19–75 ms, which corresponds to MARI of roughly 15–60 ms. Values decline with age and with increasing heart rate.
Low MARI
- Weak vagal regulation, sympathetic predominance
- Stress, fatigue, lack of sleep, acute illness, fever
- Ageing, physical inactivity, obesity
- Persistently low values: hypertension, heart failure, coronary disease, diabetic autonomic neuropathy — associated with higher cardiovascular risk
High MARI
- Strong vagal tone: rest, sleep, good aerobic fitness
- Slow, deep breathing during the recording
- Falsely high values: extrasystoles, atrial fibrillation, artefacts — check the ECG
What affects MARI and how to improve it
- Measure lying or sitting quietly, at the same time of day, before coffee and exercise.
- Regular aerobic exercise, enough sleep and slow-breathing practice increase vagally mediated HRV.
- Alcohol, nicotine, overtraining and chronic stress reduce it.
Discuss your results with a doctor if MARI stays low for your age over a long period, especially with palpitations, breathlessness, high blood pressure, diabetes or known heart disease, or if very high values coincide with an irregular pulse.
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
- Shaffer F, Ginsberg JP. An overview of heart rate variability metrics and norms. Front Public Health. 2017;5:258. doi:10.3389/fpubh.2017.00258
This article is for general information and does not replace a consultation with a doctor. HRV values depend on the device, recording length and conditions.
Published on 5 June 2019