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Set your smartwatch alarm. You’re about to be barraged by tons of hype about the health benefits of the Apple Watch. Unfortunately, it won’t include essential information and data that can put these claims in proper perspective.

Last year, Apple CEO Tim Cook tweeted how an Apple Watch detected a rapid heartbeat in an 18-year-old girl, who said the device saved her life. Now, with the presentation on Saturday of findings from an enormous Apple Watch study at the American College of Cardiology meeting in New Orleans, the hype meter is about to go to 11.

The Apple Heart Study, conducted by Stanford University researchers and sponsored by Apple, evaluated the ability of the Apple Watch to detect atrial fibrillation, a common heart disorder also known as A-fib, in an astonishing 400,000 participants.


A-fib affects somewhere between 3 million and 6 million Americans, most of them over age 65. In some people it’s silent, causing no symptoms. In others it causes heart palpitations, dizzy spells, and shortness of breath. Whether or not a-fib causes symptoms, it quadruples the risk of having a stroke.

While the Apple Heart Study will tell us many new things about the watch, what it won’t do — what it can’t do — is provide any insight into the device’s real overall effects on health. This is because the study was not a randomized controlled trial, the gold standard of medical research.


Instead, it is a purely observational study designed to see whether the Apple Watch’s heart pulse monitor can identify people who have a-fib. But because the study does not contain a control arm, it can’t say what might have happened to a similar group of 400,000 people who did not use the Apple Watch. The study will therefore be a rich source of anecdotes but, as good scientists know, anecdotes aren’t data. (Just because your friend’s uncle got rich playing the lottery you shouldn’t conclude that it’s a good idea to spend your next paycheck on the lottery!)

Some people will inevitably argue that saving the life of a young girl, as related by the Apple CEO, is proof the watch can contribute to our health. But that assumption may not hold up if the cost of the benefit means harm to many other healthy people.

When evaluating a new drug or device, it is a cardinal rule that the benefits must be weighed against the risks. With some drugs and devices, the risks are obvious. In others, such as with something as apparently benign as the Apple Watch, the risks may be less immediately apparent. Nevertheless, they can be real and potentially significant.

To understand these potential harms, it’s important to recognize that no medical test is perfect. There are always false negatives, in which the device fails to detect a real problem, and false positives, in which it wrongly detects a problem that doesn’t exist.

Harm occurs from these in several ways. One is when people who have atrial fibrillation don’t consult a doctor about symptoms such as heart palpitations or shortness of breath because they feel falsely reassured by the absence of any alert from their Apple Watch. The new study provides no evidence about the true rate of false negatives in the study population because the researchers did not independently monitor people in whom the device did not detect a-fib.

A far more common problem will be false positives, in which the watch delivers an alert to people who do not have a-fib. Imagine the impact of such an alert on a perfectly healthy person who suddenly believes he or she might have a heart rhythm disorder. Then imagine the impact on a health care system as thousands of young, healthy people suddenly want to schedule appointments with cardiologists. Is this really the best use of time for those seeking care or those providing it? Can our already overburdened health care system absorb this sort of influx? What will happen to the underserved sick and elderly people who really do need the services of a cardiologist?

You may think it’s a mistake to focus on false positives and false negatives because the watch is highly accurate at detecting a-fib. But experts who have looked at this issue already know that there will be a large number of false positive alarms, far more than the number of accurate positive alarms. Venkatesh Murthy, a cardiologist at the University of Michigan who has studied this issue, told me that more than 90 percent of irregular rhythm alerts in younger and middle aged users will be false alarms.

Even if the Apple Watch does work correctly, it is by no means clear it will generate benefits to the public’s health. Most episodes of a-fib are not harmful. There has been an enormous amount of research on people with a-fib who enter the health care system through conventional means — most often by going to a doctor about their symptoms or by having the problem diagnosed during a physical examination. The medical community has a fairly good idea about which of these patients are most likely to benefit from further treatment, although I must acknowledge that there is some controversy even here.

But the medical community has no idea how to respond appropriately or efficiently to the large number of people who will be identified as having a-fib by the Apple Watch alone. Most of these people — young and tech-savvy — will almost certainly be at low risk for a stroke or other harmful consequence of a-fib. It is entirely possible that the vast majority would do fine until their heart problem was identified by traditional means.

It is also possible that the harms of the treatments they are offered could outweigh any reduction in stroke risk. In fact, the blood-thinning drugs used to prevent stroke in people with a-fib can make it difficult to stop bleeding and can even lead to an uncommon but serious kind of stroke caused by bleeding into the brain.

There no evidence yet that treating people for a-fib that’s first detected by an Apple Watch will result in a net benefit when strokes averted are balanced against excessive bleeding and complications from procedures for a-fib like catheter ablation or the implantation of a Watchman device. And the Apple Heart Study will not provide this proof.

There’s a lot of enthusiasm out there for new, high-tech devices like the Apple Watch, but it is extremely difficult to find thoughtful perspectives on the complex medical issues they raise. We are in the middle of an overwhelming rush to embrace new technology and make health data available to everyone. This movement is fueled by Apple and other technology companies that are starting to spread some of their enormous wealth in the medical community, laying the groundwork for their expansion into this field.

Unfortunately the immediate response to this new study is likely to be even more irrational exuberance and premature implementation of a potentially harmful technology before there is any evidence showing that the Apple Watch actually improves human health.

Larry Husten writes the CardioBrief blog.

  • Let’s say you get a sketchy rhythm and want to go to the doctor. You’ve yet to see a doctor for a heart illness ever, but the watch says you have an inconclusive heart rhythm. You’re scared. But, once you enter the doctor’s office, and tell that doctor your story, you’re now at the mercy of a horribly litigious health care system. What does that mean? Well, you might be getting a drug, based purely on a watch’s assessment of your rhythm, your history of mild shortness of breath (while you were running, you should appreciate the sarcasm there), a doctors fear of NOT DOING ANYTHING, (which would be the correct action) and a lawyer ready to pounce on any malpractice. Now what? You’re on a new drug, we’ll call it a blood thinner. You start it, and cut yourself. You are now bleeding profusely and its difficult to stop. Let’s say you hit a joint and start bleeding into the joint. Let’s say what you really have is hypertension and you rupture a small artery somewhere near your brain…guess what’s going to happen, all bc you bought a watch. Feel free to add to this scenario that has the potential to be played out not only hundreds of times per day, but with more outcomes. Respectfully stated.

    • Are you kidding me?? Since when is a doctor scared of not doing anything? They hardly ever do anything even when action IS needed! They only act when finally given clear indisputable evidence that action is needed. So if they gave someone blood thinner based purely on the reading of the Apple Watch and don’t even run their own tests first, then that’s their fault, and they SHOULD have litigation pending against them. Every patient has the right to sue if they feel that they’ve been wronged. I don’t know why you would call that a bad thing. Stop with the fear-mongering

    • And if what you really have is hypertension and you risk rupturing an artery in your brain, I don’t know what the Apple Watch could possibly change about that either in a negative or positive way. The watch wouldn’t somehow prevent you from getting the treatment you need, and similarly one wouldn’t be expecting it to tell you if you had hypertension. The majority of your fears are unwarranted

  • Yes, my Iwatch does a good job detecting my Afib, which is now under control, no episodes for a year. I am 75. My Afib was converted to sinus rhythm the first time. I am also now under the care of a cardiologist and taking zarelto. The watch monitors my heart rate accurately as I back it up with a pulse oxcymeter, Every pharmaceutical that is prescrbed to Afib patients has been tried and every one of them made me sick and unable to function.

  • There are no laws or standards anymore regarding the deceptive marketing and hype surrounding these devices. They will most likely be proven to be worse than useless or used for nefarious purposes, like workplace monitoring of employees. No data will be collected, about the damage and injuries these devices cause or the added stress. Time after time these devices are proven useless, yet our industry beholden government allows these corporations to deceive,mislead and even kill Americans. Like everything else it is buyer beware! The Device manufacturers designed these for profit potential and data collection, not anyone’s well-being.

    • For people like me AF the are a godsend. I can detect when my HR hits 180 plus and monitor it. My episodes last for Up to 12hours and I know exactly when I should head off to the ER…don’t tell me the health system will go broke, it should be free to all anyway. I pay my insurance and I expect a service when I need it. My condition is not self inflicted because I drink or smoke or overeat…it’s an illness that has devastating effects on ones wellbeing and peace of mind and only those who suffer it know. A doctor once told me it’s better to have a heart attack and get treated for it rather tha think you are going to die or have a stroke 150 times a year. And stroke from AF are devastating.

  • Unlike the rational discussions on sites like, this article is biased against the benefits of the heart monitoring by the AW4, the alerts generated by that monitoring, and finally the EKG that can be taken by the user.

    The user can take an EKG if prompted by an alert, or if they feel the onset of symptoms. The AW4 filters the EKG so a very clear reading is obtained. It only identifies AFib. However, it may report “Inconclusive”, and when I consulted a cardiologist Premature Atrial Contractions were diagnosed.
    The other monitoring and EKG system for AW is the Kardia band. EKG reading can be emailed for expert analysis, and if abnormalities are detected, there is an urgent warning “seek medical advice within 24 hours”. KARDIA also provide continuous heart monitoring which is very reassuring, but while this is on the activity measuring is turned off.
    In summary, a biased article that has the effect of misleading and alarming people.
    Disclaimer- I have no relationship with Apple or Kardia, but both are my trusted companions despite my awareness of their limitations. 52 years of happy marriage will do that for you.

  • Sure, a device that tells people to consult a doctor when something might be wrong is going to destroy medicine as we know it. As we know, you should consult a doctor only when you already have a firm diagnosis and an accurate prognosis. Down with early detection and false positives.

  • You imagine an (American) medical universe where a patient jumps from an unwarranted AFib diagnosis to blood thinners or an ablation without more tests or a doctor in between. The watch does get the patient in the door (perhaps unnecessarily), but from there on in, we rely on our existing healthcare system to figure out what to do next. Your worries about this product causing serious harm or unneeded interventions are overblown.

  • While a sanity check for a country that believes everything it reads on Facebook is a good thing, did you really just end the article claiming the Apple Watch is not a positive for health? The entire article is so negative for a device that has helped promote physical activity and exercise. You should be applauding it unless you actually don’t want heart health to improve.

  • You describe the technical aspects and issues surrounding unstructured screening, especially with (yet) fairly poorly calibrated test equipment well.
    However, I’d like to point out that well before the apple watch (and similar wearables) the medical world is already chockfull of unwarranted screening, unintended consequences, significant harm, advice based on observational retrospective studies etc. etc.. A little less hubris please – a country that spends twice per person what other developed countries spend on healthcare with considerably worse outcomes may not have much of an argument here – at least not the way it is structured. Respectfully submitted

  • Apple watch, as other smartwatches, is merely able to measure the puls rate with error levels similar to Garmin or other smartwatches. This is common for all devices which do not use at least two electrodes placed within sufficient distance on the body. So, while the ECG is a nice sales feature, it can not be treated by any mean as a trusted source of information for medical purposes.

    • This is incorrect – the Apple Watch 4 has 2 electrodes. The other 2 devices that measure heart activity are the Kardia devices, and the Polar chest straps.
      Garmin wrist devices, like all other except the preceding 3, rely on lights shining on blood vessels to measure heart rate only – they cannot track rhythm issues like Atrial Fibrillation.

      The new Kardia device will give greater accuracy.

      This site seems to attract folk who are determined to trash the Apple Watch 4. It has its limitations but intelligent users can obtain great benefits.

      I have both Kardia and AW4 – I lent my AW4 to a family member recently pending her heart test results. The repeated normal reading were reassuring until the good news from all her tests reading normal were received.

      I have a preference for Kardia as I can send ECGs for expert readings, and get results very promptly.

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