What is heart rate variability?
Heart rate variability is where the amount of time between your heartbeats fluctuates slightly. These variations are very small, adding or subtracting a fraction of a second between beats.
These fluctuations are undetectable except with specialized devices. While heart rate variability may be present in healthy individuals, it can still indicate the presence of health problems, including heart conditions and mental health issues like anxiety and depression.
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Is heart rate variability like an arrhythmia?
Heart rate variability is a normal occurrence, and it isn’t an arrhythmia on its own.
The normal beating of your heart is called “sinus rhythm.” When your heart is beating normally but the variability between heartbeats is greater than 0.12 seconds, this is called “sinus arrhythmia.” Heart rate variability can sometimes meet the criteria for sinus arrhythmia.
Sinus arrhythmia is usually due to breathing (this is called respiratory sinus arrhythmia), which is part of a normal reflex of your heart and circulatory system. However, when sinus arrhythmia isn’t caused by breathing, it may be a sign of another heart problem that does need assessment by a healthcare provider.
How does heart rate variability work?
Your heart beats at a specific rate at all times. That rate changes depending on what you're doing at the time. Slower heart rates happen when you're resting or relaxed, and faster rates happen when you're active, stressed or when you’re in danger. There is variability in your heart rate based on the needs of your body and your respiratory patterns. Certain medications and medical devices — such as pacemakers — can also affect your heart rate variability. Your heart rate variability also tends to decrease normally as you get older.
Whether you’re awake or asleep, calm or stressed, your heart has to be able to react to changes in your life and surroundings. But it doesn’t know when to react on its own, so it relies on another body system for help.
Parasympathetic vs sympathetic branches and heart rate variability
Your brain and nervous system support your heart. Your senses — sight, sound, smell, taste and touch — feed information to your brain about everything around you. Your brain has a direct line to your heart, telling your heart when it needs to speed up and work harder.
This direct line to your heart is your autonomic (pronounced “auto-nom-ick”) nervous system. This is a part of your brain and a set of nerves that operate without you thinking of them, even when you’re asleep. It’s divided into two main parts: your sympathetic nervous system and your parasympathetic nervous system.
In general, the sympathetic and parasympathetic nervous systems work like so:
- Sympathetic. This is where your “fight-or-flight” response comes from. It manages increases in heart rate and blood pressure in emergency situations.
- Parasympathetic. This helps balance out the sympathetic nervous system and controls the natural relaxation response, especially after you’ve been in fight-or-flight mode. It controls slowing your heart rate and blood pressure, among other things, especially when you’re taking it easy.
Here’s an example of how these two parts of your nervous system work together.
If you think you’re in danger, you get scared or startled, or if you’re anxious about something, your sympathetic nervous system kicks in and starts the fight-or-flight response. Your body releases adrenaline so you can react faster. Your heart rate goes up, just in case your muscles need more blood and oxygen because of physical activity.
Once the situation that put you into fight-or-flight mode is over, your parasympathetic nervous system takes the lead. It tells your heart rate to slow back down and lowers your blood pressure. It also tells various systems of your body to relax or go back to how they normally work.
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Why is heart rate variability a good thing?
Your body has many systems and features that let it adapt to where you are and what you’re doing. Your heart’s variability reflects how adaptable your body can be. If your heart rate is highly variable, this is usually evidence that your body can adapt to many kinds of changes. People with high heart rate variability are usually less stressed and happier.
In general, low heart rate variability is considered a sign of current or future health problems because it shows your body is less resilient and struggles to handle changing situations. It's also more common in people who have higher resting heart rates. That’s because when your heart is beating faster, there’s less time between beats, reducing the opportunity for variability. This is often the case with conditions like diabetes, high blood pressure, heart arrhythmia, asthma, anxiety and depression.
How is heart rate variability measured?
The variances in your heart rate are very small, so it takes specialized equipment or devices to detect them. Modern technology has reached a point where non-medical devices that can track heart rate variability are affordable and easy to find.
In a medical setting, an electrocardiogram machine (also called an EKG) is usually used to detect heart rate variability. This device, which measures the electrical activity of your heart using sensors attached to the skin of your chest, is highly accurate. Healthcare providers can also send you home wearing a monitor that tracks heart rate variability continuously for longer periods of time. The length of time that your heart rate variability is monitored can be anywhere from a few minutes to 24 hours. Longer monitoring times tend to give the best data.
Outside of a medical setting, there are several devices commonly used by athletes, especially runners. These often consist of a device attached to a band that wraps around your chest. Some look like pulse oximeters (devices that attach to a finger and measure your pulse and blood oxygen level) but are more sensitive and accurate.
The majority of wrist-worn fitness devices and trackers track your heart rate through your skin. Unfortunately, this means they usually aren't sensitive enough to detect heart rate variability accurately.
