tachogram

A tachogram is a graphical representation used in heart rate variability (HRV) analysis that displays successive inter-beat intervals, usually the RR or NN intervals, over time. The typical tachogram plots the interval length on the vertical axis and the beat number or elapsed time on the horizontal axis. It is derived from ECG data by detecting ventricular R peaks and computing the time between consecutive peaks.

Tachograms are used to visualize beat-to-beat variability and nonstationarities in heart rate. They can reveal trends, drift, or abrupt changes that may indicate physiological responses to activity, respiration, sleep, or autonomic modulation. A relatively flat tachogram suggests stable RR intervals, while larger fluctuations indicate higher short-term or long-term variability. Ectopic beats, artifacts, or irregularities can appear as outliers or abrupt discontinuities in the plot.

In HRV analysis, the tachogram is one of several tools. It complements time-domain measures (such as SDNN and RMSSD) and frequency-domain analyses, as well as the Poincaré plot, which provides a scatter representation of successive intervals. Proper interpretation requires attention to data quality, artifact removal, and segment length, since nonstationarities and measurement errors can distort the tachogram and subsequent HRV metrics. Tachograms are widely used in clinical, sports, and sleep research to assess autonomic function and cardiovascular health.