Library · Physiology
Heart rate variability
Make it clearer
The heart does not beat like a clock. Even when the pulse feels steady, the gap between one beat and the next is not identical to the gap before it, and that difference is called heart rate variability. It is like the steps you take when you walk: they look identical, but no two take exactly the same time.
The underlying rhythm is set by the sinoatrial node, the group of heart cells that works as the pacemaker. The fluctuation on top of that rhythm comes from the conversation between the heart and the brain and from the autonomic nervous system, the part of the nervous system that works without you thinking about it.
One example shows up in your breathing. The rhythm rises and falls with each breathing cycle, and that back-and-forth is called respiratory sinus arrhythmia. It mostly reflects the parasympathetic branch, the one that puts on the brakes.
One thing is worth clearing up, because the opposite gets repeated a lot: more variability is not always better. There are pathological conditions, meaning states of disease, that also produce variability.
In brief
Heart rate variability is the fluctuation in the time intervals between adjacent heartbeats.
Like steps when you walk: they look identical, but no two last exactly the same.
The sinoatrial node sets the baseline rhythm, and the fluctuation comes from heart-brain interaction and the autonomic nervous system.
The high-frequency band reflects parasympathetic activity: respiratory sinus arrhythmia, the rise and fall of the rhythm with each breath.
More variability is not always better: some pathological conditions produce it too.
Sources (2)
- Frontiers in Public Health, via PubMed CentralAn Overview of Heart Rate Variability Metrics and NormsPublished
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Sinoatrial Node, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
Updated