Ellipse
Ellipse — the area of the Poincaré-plot ellipse (S) — is a geometric heart-rate-variability index. Each heartbeat interval is plotted against the next one, an ellipse is fitted to the resulting cloud of points, and its area summarises the overall variability of the heart rhythm: short-term (beat-to-beat) and long-term components together.
The Poincaré plot (scatterogram)
A Poincaré plot is a "map" of the heart rhythm. For every beat a point is drawn whose horizontal coordinate is the current interval RRn and vertical coordinate the next interval RRn+1. If the rhythm were perfectly regular, all points would merge into one dot on the diagonal (the line of identity). In a healthy heart the points form an elongated cloud — a "comet" or "torpedo" — along the diagonal.
How the ellipse is calculated
SD1 — the width of the cloud perpendicular to the line of identity — describes beat-to-beat variability and depends mainly on the vagus nerve. SD2 — the length along the line — describes slower fluctuations and total variability. Example: SD1 = 30 ms and SD2 = 70 ms give S = π × 30 × 70 ≈ 6600 ms². The ratio SD1/SD2 characterises the shape of the cloud and is sometimes used as an additional index.
Interpretation
Small ellipse area
- Low overall HRV — rigid rhythm controlled mainly by the sympathetic system
- Stress, fatigue, illness, fever, dehydration
- Ageing, sedentary lifestyle
- Persistently small area: heart failure, after myocardial infarction, diabetic autonomic neuropathy — associated with increased cardiovascular risk
Large ellipse area
- High HRV and good autonomic flexibility: rest, sleep, good fitness
- Falsely large area: extrasystoles and artefacts create points far from the main cloud; atrial fibrillation produces a scattered "fan" instead of an ellipse
The shape of the scatterogram is as informative as its area: a "comet" is typical of healthy people, a small "ball" of sympathetic dominance, and separate clusters or a "fan" suggest arrhythmia. In Russian-language literature the same parameter is described as S, the area of the ellipse covering the main cloud of the scatterogram, an analogue of total variability.
Consult a doctor if the ellipse area stays small for your age, or if the scatterogram shows scattered points, several clusters or a fan shape — this may indicate extrasystoles or atrial fibrillation, which require an ECG.
References
- Brennan M, Palaniswami M, Kamen P. Do existing measures of Poincaré plot geometry reflect nonlinear features of heart rate variability? IEEE Trans Biomed Eng. 2001;48(11):1342–1347. doi:10.1109/10.959330
- Tarvainen MP, Niskanen JP, Lipponen JA, Ranta-aho PO, Karjalainen PA. Kubios HRV — heart rate variability analysis software. Comput Methods Programs Biomed. 2014;113(1):210–220. doi:10.1016/j.cmpb.2013.07.024
- 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
- Voss A, Schulz S, Schroeder R, Baumert M, Caminal P. Methods derived from nonlinear dynamics for analysing heart rate variability. Philos Trans A Math Phys Eng Sci. 2009;367(1887):277–296. doi:10.1098/rsta.2008.0232
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 10 July 2019