Apple Watch accuracy ?

According to a study by the American College of Cardiology, May 29, 2024, for Apple Watch “the positive predictive value (PPV) for AF was 84%.”

I use a Cardio Mobile and I wonder about the accuracy of this device since it is so susceptible to interference from electrical and electronic signals. I was diagnosed with AFIB and the reading was always Possible AFIB.

This is what I read..” According to the Apple Heart Study, which involved an impressive 419,297 participants, only 34% of AFib detections by the Apple Watch were confirmed as true AFib upon further testing. This means that approximately two-thirds of these alerts were false alarms.”

I have a Kardia mobile device (it's attached to an Enron blood pressure machine so it can be set up to measure both blood pressure, heart rate and an EKG. I have paroxysmal A-fib and when I've checked my EKG when I suspected I was in A-fib, it's always read "possible" A-fib too.

I suspect the reason for that is a "CYA" move on the part of the company, they don't want a person diagnosing themselves with A-fib based solely on Kardia readings, so adding in the element of uncertainty in calling an EKG that shows even a typical A-fib pattern makes allowances for errors on the part of the operator, possible electrical interference or any other variable that may influence an EKG reading. There are disclaimers in the Kardia literature that state EKG readings should be verified with medical professionals to make a valid diagnosis of an arrhythmia like A-fib. It's my understanding that if you join Kardia's subscription service, sending them your EKG results allows for a medical professional to check those results and to interpret them. You'd get those results back as "Atrial Fibrillation", or whatever it is they could see in those EKGs. Sending your questionable EKGs like "possible A-Fib" to a professional, for instance, to your own doctor instead of the Kardia subscription service allows for their validation of the results you got from your Kardia mobile.

I recently had an interesting experience with this. I had an episode of A-fib late one night, my episodes usually last just a few seconds but this one went on and on. I decided to see if A-fib was what I was feeling, set up my Kardia, and sure enough, the heart rate was elevated with a result of "possible A-fib". I also have a pacemaker with a remote monitor that "rats" on me when those episodes come up, and I noted from looking at my patient portal at the cardiologist's office that the monitoring company had sent them a report with the date and time I was having this relatively prolonged A-fib episode. This report was outside the normal quarterly reports it sends, so it had to be reporting the A-fib episode.

Well, I printed out a copy of that A-fib episode I had picked up with my Kardia, to show it to the cardiologist during my recent appointment. He verified that they had gotten the report from the monitoring company showing a 2 hr+ long episode of A-fib and another one soon after lasting about an hour. He looked at the report from my Kardia, kind of laughed at the dates and times printed on it that were within the dates/times reported by the monitoring company, and said "yup, that's A-fib all right".

All-in all, I don't think the Kardia mobile calls an EKG for A-fib unless it meets all the criteria for A-fib, any question it's more likely to call it "unclassified", but there can be errors. So it's going to err on the side of caution, and add that element of uncertainty by calling it "possible" A-fib, which in any case of doubt should be verified with a professional. At least that is my take on it.

This is almost certainly not due to the accuracy of the sensor, but due to the WAY people use, and wear, their watches. Some like watches loose, some don't mind their straps snug. Some wash the backs of their smart watches regularly, some don't. Sensors blocked by schmutz, or sensors that are continually being jostled and lifted away from contact with the underlying skin, will have compounded rates of errors of all kinds.
I use a Samsung Galaxy watch since my phone preference is Android. I have two versions, one a nicer/dressier/newer Galaxy 6 that didn't need any updating, and an older Galaxy 4 that did need a firmware update before it could measure ECG, blood pressure, and blood oxygenation saturation. I wear the older 4 most days. It detected a recurrence of AF when the missus and I were visiting our youngest and her two young toddlers. I felt the AF return (this was post ablation), and made the app record my current heart rhythm. I uploaded that file to my PC and attached it to an email to my electrophysiologist. He accepted that record without question, and it did clearly show the erratic R-R intervals, and my watch did show no P-waves, both of which are the definitive indications of AF.
I haven't looked for formal assessments of my Galaxy's accuracy, but it has to be much better than 34%, and I'm sure the vaunted Apple watches are much better than that as well. It's the wide variance in their wearer's use of them that should account for this low assessment This is strictly my opinion, of course, and it is without the benefit of seeing the report and what methods were used to control for confounds like wearer variations in the use of their watches.

Thank you for your post. I've an Apple watch I purchased to help monitor my heart. Never thought to check for schmutz. I did and there it was. Now its gone. Appreciate the tip. Wishing you a long and healthy life 😍

When I think I’m in A-fib usually my watch reports “possible “ or “ inconclusive”. I use my Kardia mobile which will verify a-fib.

I've worn an Apple Watch for a couple of years, and I do not believe it accurately measures Afib. In July 2024 I had a pulsed field ablation (Mayo Jacksonville), and a subsequent Holter monitor showed zero Afib. However, since then my Apple Watch weekly report has continued to show Afib, ranging from 7% to 25%. My cardiologist said he thinks the watch confuses my premature atrial contractions (I have a 10-12% load) for Afib. Even then, how do I get an Afib report of 7-25% if the PAC load is no more than 12%? I have no idea. I continue to record the results, but I'm skeptical that I'm getting meaningful data.

I too have great doubts about the accuracy of the Apple Watch. It seems to pick up/confuse other rhythms and reports them as AFib.

My Apple Watch has been very accurate. I have occasional Afib? maybe twice a year. I know immediately when I go into Afib as my bpm go from normal to around 125. My watch always confirms this an hour later and continues with updates until I go out.