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    VLF
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    VLF

    VLF power: very slow heart rate oscillations, slow regulation and prognosis.

    VLF — very-low-frequency power — is the part of heart-rate-variability power in the band 0.0033–0.04 Hz, i.e. oscillations with periods from about 25 seconds to 5 minutes. It reflects slow regulatory mechanisms — thermoregulation, the renin–angiotensin system, hormonal and metabolic influences and activity of higher (suprasegmental) brain centres. Low VLF power is one of the strongest HRV predictors of mortality after myocardial infarction.

    Heart rate variabilityFrequency domainSlow regulationPrognosis
    Frequency band0.0033–0.04 Hz
    Oscillation period≈ 25 s – 5 min
    Unitms²
    Recommended recording≥ 5 min, ideally 24 h

    What VLF reflects

    The physiological origin of VLF is less clear than that of LF and HF. Experimental and clinical data link it to several slow processes: periodic changes of vascular tone in thermoregulation, the renin–angiotensin–aldosterone system, physical activity, and intrinsic rhythms of the heart's own nervous system. Because several of these influences are mediated by the sympathetic system and higher brain centres, VLF is sometimes described as a marker of "central" or humoral–metabolic regulation.

    Power spectrum of heart rate variability with very low frequency band up to 0.04 hertz, low frequency band 0.04 to 0.15 hertz and high frequency band 0.15 to 0.40 hertz; total power is the area under the whole curve VLFLFHF ≈ 0.1 Hz: baroreflex≈ 0.25 Hz: breathing (vagus) 00.040.150.40 Frequency, HzPower, ms²/Hz
    Figure 1. Heart-rate power spectrum. VLF (violet) covers the slowest oscillations below 0.04 Hz; a reliable estimate requires sufficiently long recordings.

    Measurement

    A 5-minute recording contains only a few complete VLF cycles, so short-term VLF estimates are imprecise and strongly affected by trends and movement. The Task Force considers VLF in short recordings of dubious value and recommends evaluating it in long-term (24-hour) recordings. VLF is included in total power but excluded from normalised LF and HF units.

    Interpretation

    Low VLF

    • In 24-hour recordings after myocardial infarction, low VLF and ULF power had the strongest association with mortality among frequency-domain measures
    • Heart failure, chronic inflammation, diabetes
    • Chronic fatigue, exhaustion of adaptive reserves

    High VLF

    • Physical activity, posture changes or talking during the recording
    • Strong emotional reactions, sleep-disordered breathing (periodic breathing in sleep apnoea)
    • Non-stationary signal or artefacts
    When to see a doctor

    VLF is not used alone for diagnosis. If VLF and other HRV indices remain low over a long period, especially after a heart attack, with heart failure or diabetes, discuss the results with a cardiologist. Very large VLF oscillations during sleep with snoring may suggest sleep apnoea.

    References

    1. 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
    2. Bigger JT Jr, Fleiss JL, Steinman RC, Rolnitzky LM, Kleiger RE, Rottman JN. Frequency domain measures of heart period variability and mortality after myocardial infarction. Circulation. 1992;85(1):164–171. doi:10.1161/01.CIR.85.1.164
    3. 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 1 July 2019