Our latest research introduces heart rate tracking through a wearable device as a new way to discover seizure likelihood
What are seizure cycles?
Our research has well established that seizures occur at certain, regular intervals. For instance, some people’s seizures tend to follow daily, weekly, or monthly rhythms — or other unique cycles like every 11 days or five (5) weeks. Seizure cycles are common, although they are different for everyone. Using cycles estimated from historical seizure times, ‘seizure likelihood’ can be forecasted and used to determine periods when someone has a high, low, and baseline likelihood of having a seizure.
Using wearable devices to improve seizure cycle tracking
Our research has proven that seizure likelihood can be forecasted by combining data from wearable devices and self-reported seizures logged in the Seer app.
The best way to track someone’s cycle is to continuously measure their brain activity since it is ultimately the brain that causes seizures to occur. Long-term recordings of brain waves show very clear, multiday cycles that are strongly predictive of seizure likelihood.
Previously, these cycles have only been found using implanted brain recording devices, which are not appropriate for everyone. So the Seer Research team studied other organs which are connected to the brain, such as the heart, which might also show long-term cycles related to seizure likelihood.
Our research participants wore a Fitbit smartwatch to record data on heart rate, stress, sleep and physical activity, and used the Seer app to record events they believed to be a seizure. It’s important to note that the wearable devices don’t detect seizures, rather they record other health data, such as heart rate, which show changes connected to seizure timing.
Our research found that cyclic rhythms outside the brain could strengthen seizure cycle tracking and be tracked with a non-invasive wearable device.
Heart rate cycles are linked to seizure cycles
For the first time, our research team was able to track long-term rhythms using heart rate, and relate those changes to someone’s likelihood of having a seizure.
Our studies tracked participants’ long-term seizure cycles and found slow, rhythmic changes in people’s average resting heart rate. Heart rate cycles were different for each person. For instance one person might show a rhythm of around 6 days, whereas another person might have a 14-day cycle.
Our research scientists use mathematical analysis to extract the strongest rhythms from these signals, and the cyclic pattern can be seen just by looking at charts of recorded data.
Figure 1. A graph showing two examples of different heart rate cycles.
The other important finding was that heart rate cycles were linked to seizure risk cycles for many people. Gradual changes in resting heart rate that build up and build down over many days could indicate when seizures are more or less likely to occur.
Figure 2. An example of how seizure timing is linked to heart rate cycles.
Like seizures, the cause of these slow heart rate cycles remains a mystery we are working to solve — however, we can now use heart rate cycles to monitor seizure likelihood.
Understanding the connection
There are many bi-directional connections between the brain and the heart so it is possible that brain excitability could affect heart rate or vice versa. However, it is also possible that there is no direct (causal) link between cycles of heart rate and seizures.
We don’t yet know whether the same changes in the brain that lead to seizures could also drive heart rate cycles. This question is the focus of ongoing research.
People with epilepsy may experience other alterations in their cardiac function. For instance, for some people, heart rate increases in the minutes to hours before a seizure. Stress and hormonal changes are also reported to be seizure triggers and have been known to affect heart rate. For some women, their menstrual cycle could be linked to monthly rhythms of both heart rate and seizures. However, heart rate cycles and seizure cycles are observed with equal frequency in men.
Interestingly, our study found heart rate cycles exist in people without epilepsy, and this led our team to hypothesize that there are probably other mysterious slow rhythms affecting human biology. Ultimately, researching the cause of these other long-term cycles might help us to understand the cause of seizure cycles.
Knowing when a seizure will occur remains unpredictable, but we can create a warning of when someone is more likely to have a seizure through the Seer app.
This new study shows that long-term seizure cycles can be tracked using a smartwatch and is an important step forward in developing a seizure cycle tracking app for people with epilepsy. However, there’s more to uncover.
Our researchers believe that for people with epilepsy these many biological rhythms can combine to create conditions that are conducive to seizures. While seizure onset may retain an element of unpredictability, if we can track enough key biological rhythms we hope to be able to warn people of high-risk conditions.
The relationship between biological rhythms and seizure cycles are not yet fully understood. Additional research will continue at Seer to understand seizures and further improve the lives of people living with epilepsy.