Can a Fitness Tracker or Smartwatch Help You Live Longer?
Is the Future of COVID-19 in Wearables?
More than 33 million people worldwide have tested positive for COVID-19.  Could fitness trackers and smartwatches be used for the early detection of COVID-19 and help prevent its spread? More data is needed to know for sure, but it’s possible that a fitness tracker or smartwatch could pick up on temperature, heart rate, and/or respiratory rate changes before you notice a change or have symptoms of COVID-19. 
There are currently ongoing studies in this area, including a phase 3 clinical trial for the COVID-19 vaccine in Abu Dhabi using the WHOOP fitness band. These studies will hopefully give us more definitive, scientifically validated data on whether or not fitness trackers and smartwatches are helpful for the early detection of COVID-19.
The ECG on Your Wrist
COVID-19 has shown us that having the option for testing from home is an area that’s becoming more and more useful. One day we may all have a mini-medical office at home. Consider all the people who have bought home pulse oximeters this year to measure their oxygen levels because of COVID-19.
About 21% of Americans use a smartwatch or wearable fitness tracker according to research from the Pew Research Center.  Some wristband fitness trackers and smartwatches are able to alert the wearer to an irregular pulse, such as possible atrial fibrillation. Some have the option to generate an ECG as well. There are also other wearable ECG options, like clothing, that are being studied.  However, I’m only going to review the data on wristband fitness trackers and smartwatches with ECG capabilities, as this seems to be the most popular home ECG option at this time.
How Do Wristband Generated ECGs Work?
The gold standard for ECGs is a 12-lead ECG, which is what’s done at the doctor’s office or hospital. There are now fitness tracker and smartwatch options that can take a 1-lead ECG for you wherever you are. The wristband of your device in theory could be moved around your body to produce a multi-lead or 12-lead ECG, but so far there isn’t enough data to say that this is equivalent to a standard 12-lead ECG.
An ECG is generated on a wristband fitness tracker or smartwatch based on photoplethysmography (PPG) technology which can detect blood flow to determine your pulse and then your device will use machine learning algorithms to try to identify your heart rhythm as normal or irregular.
Other options to identify abnormal heart rhythms include Holter monitors, event monitors, and insertable or implantable cardiac monitors.  These options may not be as convenient for most people as fitness trackers or smartwatches, but they are generally more accurate for detecting abnormal heart rhythms.
Are Wristband Generated ECGs Helpful?
Although there have been many cardiac complications associated with COVID-19 , so far there hasn’t been strong data that ECGs from wristband fitness trackers or smartwatches are useful for COVID-19. However there are other potential scenarios where fitness tracker or smartwatch ECGs could be useful to you.
You can record an ECG from your fitness tracker or smartwatch when you feel palpitations or other symptoms or if your device alerts you that you have an irregular rhythm. So far fitness tracker and smartwatch ECGs have been used primarily to identify atrial fibrillation (AF).
Why is Atrial Fibrillation Important?
Having atrial fibrillation can lead to the formation of blood clots in your body, which can cause a stroke, among other things. Generally speaking the risk of stroke with AF is greater for people who are over 60 years old and/or people with underlying medical conditions like diabetes and high blood pressure.
AF is an independent risk factor for stroke, although it’s not the only cause of stroke.  It’s estimated that around 13% of people who have AF are undiagnosed. Around half of these people may be at high to moderate risk for stroke.  People with subclinical AF (very short lasting AF or AF with no symptoms) can be at risk for stroke as well. 
The Accuracy of Wristband Fitness Trackers and Smartwatches
This review is based on the data available, really more data is needed as a lot of the data isn’t the highest quality data. Some studies were funded by the company making the wearable device, so there could be bias because of that. Also some studies were done in free living conditions (normal everyday life) versus others that were done in Electrophysiology Labs where heart rhythms or heart rates were artificially induced. It could make a difference in how useful the data is if heart rhythms or heart rates are naturally occurring versus induced for the purpose of a medical study.
Wristband fitness trackers and smartwatches have been generally shown to be accurate in measuring heart rate.  But not always within a narrow range  and not always for short periods of time changes in activity level.  Heart rate detection accuracy may also decrease as your heart rate increases, for example if you exercise more intensely.  So fitness trackers and smartwatches may be more useful for looking at general trends in your heart rate and heart rate variability.
Skin color may or may not make a difference in a wristband fitness tracker or smartwatch’s ability to accurately record.  Many only use green light sensors and melanin blocks green light, so it may be harder to get an accurate reading if you have darker skin color.
There is also concern that there may be machine learning algorithmic biases for race and gender. This is already an issue in medical studies which traditionally have studied primarily white men, so existing data is already skewed. Racial and gender biases may be built into machine learning algorithms based on who’s using the device. Frequently the algorithms aren’t shared by companies with physicians or researchers for proprietary reasons, so it may be hard to account for these biases when evaluating data. 
The Accuracy for the Diagnosis of AF
Wristband fitness trackers and smartwatches have been shown to be accurate in detecting atrial fibrillation in some large studies.[16, 17, 18] However more people are also likely to get a notification that they have an irregular pulse, but don’t actually have atrial fibrillation on subsequent testing.  Compared to a traditional 12-lead ECG there is some sensitivity and specificity loss with wristband fitness tracker and smartwatch ECGs .
The reason accuracy, sensitivity, and specificity are important is because your fitness tracker or smartwatch may think you have an irregular rhythm like atrial fibrillation and you don’t or you may have an irregular rhythm and your fitness tracker or smartwatch may not pick it up. Some people have atrial fibrillation transiently for short periods of time and have a normal heart rhythm the rest of the time.
In addition, sometimes your fitness tracker or smartwatch ECG can flag artifacts as being irregular, but actually there are no irregularities in your heart rhythm. Similar to how your cell phone signal can break up, a similar thing can happen when your device tries to generate an ECG. In the doctor’s office adjustments can be made to a 12-lead ECG to try to eliminate artifacts by someone who has experience adjusting for artifacts. In addition multi-lead or 12-lead ECGs are more likely to be readable with artifacts, in a 1-lead ECG if you only have 1-lead and that lead has artifacts you don’t have any other leads to look at.
People Who Have a History of AF
Wristband fitness trackers and smartwatches may have difficulty determining what a person’s heart rate is when they are in atrial fibrillation. [21, 22] For people with a history of atrial fibrillation this information can be important to their healthcare providers to determine how to adjust their medications for atrial fibrillation. So wristband fitness trackers and smartwatches may be less useful to a person who has a known history of permanent atrial fibrillation for managing their atrial fibrillation.
The Diagnosis of Non-AF Heart Disease
There are many future uses for wristband fitness trackers and smartwatch ECGs as their capabilities improve. Wristband fitness tracker and smartwatch ECGs could eventually be used to identify when people are having a myocardial infarction (heart attack)  and ischemic changes (not enough blood flow in the heart arteries) . Moving the Apple Watch to different parts of your body to get a multi-lead or 12-lead ECG may be a promising option in the future to help with diagnosing heart attacks and abnormal heart rhythms. [25, 26]
As the accuracy and capabilities improve fitness trackers and smartwatch ECGs could also be used to identify other problems with people’s heart rhythms besides AF, like supraventricular tachycardias (fast heart rhythms), heart blocks (part of the heart’s electrical signal being blocked), and bradycardic rhythms (slow heart rhythms).
One study showed the Apple Watch may be able to capture atrioventricular nodal reentry tachycardia (AVNRT).  Another showed it may be able to record high grade atrioventricular (AV) blocks.  They may also be able to help detect ventricular tachycardia (VT).  Having documentation of these rhythms while you’re having symptoms will help your cardiologist come up with a treatment plan for you as sometimes the abnormal heart rhythms go away by the time you come in to the Emergency Room.
The Apple Watch has also been tested for measuring QT prolongation, using the watch in multiple positions across the body. This is relevant for different scenarios including for monitoring QT length when taking certain medications like hydroxychloroquine  that can cause QT prolongation and lead to cardiac arrest for some people.
But again it’s important to note just because your wristband fitness tracker or smartwatch ECG doesn’t pick up on any abnormalities for your heart, it doesn’t mean you don’t have any heart problems. If you have any concerns about having heart problems you should discuss this with your healthcare provider.
Should You Buy A Wristband Fitness Tracker or Smartwatch?
For COVID-19, in my opinion, it’s possible it could help in early detection, although there’s very limited data showing this so far. But there are many ongoing studies, like the FitBit COVID-19 study, as well as the study the Department of Defense is conducting on commonly used wearables. We’ll have to wait and see what the outcomes are from these studies.
The part that would be the most useful from fitness trackers and smartwatches theoretically for COVID-19 would be the ability to track heart rate, temperature, respiratory rate, and some options like the Apple Watch 6 have the ability to track your oxygen saturation levels, although it’s not clear yet if this tracking is accurate. The ECG capability so far doesn’t seem to have any usefulness for COVID-19. It’s likely not helpful for you to buy a wristband fitness tracker or smartwatch with ECG capabilities specifically for COVID-19.
For the purpose of atrial fibrillation my opinion is wristband fitness trackers and smartwatches with an ECG option still have room for improvement. It’s most likely to be helpful at this time if you have risk factors for atrial fibrillation or have a history of stroke or TIA (“mini stroke”). Some of the risk factors for atrial fibrillation are, but not limited to, high blood pressure, coronary artery heart disease, diabetes, obesity, chronic kidney disease, and obstructive sleep apnea. Most otherwise healthy people have a low probability of having atrial fibrillation and seem more likely to get false positive irregular pulse notifications.
In the end I would say most of my patients find wristband fitness trackers and smartwatches more useful to help them meet their fitness and workout goals. Many people find closing the rings, competing with friends and family, and tracking their workouts motivating.
Close to 80% of cardiovascular disease is thought to be preventable , and a major part of the prevention of cardiovascular disease is cardiac or aerobic exercise. Given that atrial fibrillation affects up to 2% of Americans depending on the data source [32, 33] and cardiovascular disease (which includes stroke and all heart disease) affects around 48% of Americans  and is the leading cause of death in the United States, a wristband fitness tracker or smartwatch is more useful, for most otherwise healthy people, for it’s fitness tracking capabilities.
Regular cardiac exercise can help you prevent cardiovascular disease which can help you live longer, so if you feel like a fitness tracker or smartwatch will help you do that, then it’s a good investment for your health.
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- COVID-19 Map — Johns Hopkins Coronavirus Resource Center
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- What is Atrial Fibrillation (AFib or AF)?
- Heart Disease and Stroke Statistics — 2019 Update: A Report From the American Heart Association