sdHR
sdHR — the standard deviation of heart rate — describes how much the instantaneous heart rate (in beats per minute) varies around its mean during a recording. It is a time-domain measure of overall heart-rate variability, closely related to SDNN, but expressed in the more intuitive unit of beats per minute. Reduced variability of heart rate after myocardial infarction is associated with a worse prognosis.
What sdHR shows
Each heartbeat interval can be converted into an instantaneous heart rate: HRᵢ = 60000 / NNᵢ. sdHR is the standard deviation of these values. If the heart rate swings widely with breathing, activity and rest, sdHR is large; if the rhythm is rigid, as under strong stress or in advanced heart disease, sdHR is small. Because heart rate is the reciprocal of the interval, sdHR is approximately equal to the mean heart rate multiplied by the coefficient of variation of the intervals (SDNN / MeanRR).
Example: a mean heart rate of 70 bpm with SDNN = 43 ms and MeanRR = 857 ms (CV ≈ 5 %) gives sdHR ≈ 3.5 bpm in a short resting recording.
Clinical significance
Mathematical analysis of heart rate variability shows that heart rate is regulated by many interacting mechanisms; their loss reduces variability. Clinical studies have shown that reduced heart-rate variability after acute myocardial infarction is an independent predictor of mortality and arrhythmic death. Low variability is also found in heart failure, diabetic autonomic neuropathy, chronic stress and ageing.
Low sdHR
- Rigid rhythm, sympathetic predominance
- Stress, fatigue, fever, high heart rate
- After myocardial infarction, in heart failure, autonomic neuropathy
High sdHR
- Good autonomic flexibility, rest, slow breathing
- Changes in activity or posture during the recording
- Falsely high values with extrasystoles, atrial fibrillation or artefacts
sdHR, like SDNN, depends on the length of the recording and can only be compared between recordings of the same duration and under similar conditions.
Discuss your results with a doctor if heart-rate variability remains low over a long period, particularly after a heart attack, with heart failure or diabetes, or together with palpitations, breathlessness or dizziness.
References
- Kleiger RE, Miller JP, Bigger JT Jr, Moss AJ. Decreased heart rate variability and its association with increased mortality after acute myocardial infarction. Am J Cardiol. 1987;59(4):256–262. doi:10.1016/0002-9149(87)90795-8
- 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
- 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.
Published on 11 June 2019