Artifact

HRV is calculated from a list of beat-to-beat intervals, so it is only as good as that list. An artifact is any interval that does not reflect a real, normal heartbeat. Researchers split them into two kinds:

• Technical artifacts come from the equipment. A loose electrode, a strap that shifts or a wrist that moves can make the sensor miss a beat, count one twice or time it wrongly.
• Physiological artifacts come from the heart itself, mainly ectopic beats ectopic beats Ectopic beat A heartbeat that starts outside the heart's normal pacemaker and usually comes early. Ectopic beats are common, but they distort HRV unless removed or corrected. More about Ectopic beat that start outside the normal pacemaker.

Either way, the result is an interval that is far too short or far too long. HRV metrics that compare neighboring beats, such as RMSSD RMSSD RMSSD Root mean square of successive differences: an HRV metric built from how much each heartbeat interval differs from the next. It mainly reflects vagal activity. More about RMSSD , are especially sensitive, because one bad interval creates two large differences. Lipponen and Tarvainen note that missed, extra and mistimed beat detections can significantly distort HRV values.

Good software finds and corrects artifacts before calculating HRV, either by deleting the bad intervals or by replacing them with estimated values. Different methods can give slightly different results, so the cleaning step is one of several reasons devices disagree.

You can prevent many artifacts yourself. Keep still during a spot reading, wear the strap or band snugly, and wet chest-strap electrodes before use. If one reading is far from your usual range, it is worth retaking before you read meaning into it.

The lesson How to take a good HRV reading gives a step-by-step routine.