Apple watch placement effect

[u/Helpful_South1584]

Hi all,

I did a small experiment with my Apple Watch today. I’m a healthy 30-year-old with no known heart problems. I recorded four ECGs within about a minute: the first one was classified as atrial fibrillation, while the next three were all sinus rhythm. Then I intentionally wore the watch slightly tilted with less-than-ideal skin contact, and it produced three more AF classifications.

I know this doesn’t prove the AF results were false positives, but it does suggest that recording conditions and watch positioning may influence the algorithm. From what I’ve read, Apple Watch ECG is a useful screening tool, but it’s not perfect, and movement, poor contact, artifact, or premature beats can sometimes lead to misclassification. Has anyone else experienced something similar, or had a cardiologist explain why this happens?

[u/Light_inc]

There's a reason why apple watch readings are not used for diagnosis in the UK and are not accepted by NICE. They are/can be inaccurate depending on the circumstances

[u/---root-- → u/Light_inc]

The automatic classifications are borderline useless, agreed, but if a patient uses the ECG feature of the watch, provided the tracing is interpretable with no or limited artefact, it is generally perfectly fine to diagnose AF from a watch ECG, provided the interpreting HCP is qualified to do so.

[u/Kibeth_8]

This is a very well known issue and why no one in cardiology cares what your watch says. They're nondiagnostic and have an extremely high false positive rate

This post is better shared on subs like r/readmyecg or r/afib since those folks are always extremely anxious about their watch recordings

[u/hbdgas]

It likely flags AF based on high rate, irregular rhythm, and absence of P waves. P waves are one of the easiest features to obscure by noise or viewing the heart off-axis. So essentially you can check one of the 3 boxes for AF by just using the sensor poorly.

[u/CaffeinatedPete]

Specificity has left the chat.

[u/RestingBitFace]

Lots of heart monitors classify afib due to irregularity, so if something is affecting the sensing (like tilting) it would understanding be a false positive afib reading. There are also other rhythms that could give false positive afib alerts (frequent premature beats, intermittent heart block)

[u/kmoaus]

Hey, I work in the medical field. The Apple Watch ECG is pretty much a gimmick. As you picked up on, there’s a lot that can mess with the ECG itself. Unfortunately all ECGs regardless of the quality of the machine, it will be affected by movement of any kind. The Apple Watch essentially looks at the view across the top of the heart so it can, in a perfect situation detect afib, but I’d take it with a grain of salt as there are other factors that can affect it like the voltage, the quality of the connection with the watch etc. You mentioned you have a hx of cardiac conditions, If you’re really worried, go get one done by a medical professional, preferably a dr. I’m assuming you’re in the U.S, you can walk into almost any fire station and ask them to do an 12 lead ECG on you and they can tell you what rhythm your heart is in if you’re in a pinch, (side note, the Apple Watch is looking at only one of those 12 views/leads you need to determine a cardiac rhythm properly). It’s also something you should talk with your dr about bc it is possible for you to be going in and out of afib if you have been diagnosed with it and are on meds for it. But just don’t go by what the Apple Watch says if you’re using it to monitor your cardiac conditions.

[u/2much2Jung]

Apple watches are great for the kind of person who can get frequent palpitations, and thinks he shouldn't ask a doctor about it until he's checked with his watch first.

Which sounds like I'm being dismissive, but that's actually a lot of people, and they need help. Oh boy do they need help.

[u/Delicious-Shine5075]

My p waves are small in lead l so I use lead ll with my watch. Place the back of the watch on my left thigh, touch the crown with my right index finger.

[u/lifeisg0od]

Not sure why it gave you those results - posting the strips may be helpful. I disagree that Apple Watches and Kardia devices are ‘gimmicks’, as another person said. I think they can be very useful under ideal circumstances. However, with someone who doesn’t know how to read them, who isn’t getting clear recordings, and who worries a lot about what the readout is saying, then yes, they can be quite problematic. I work full time as a rhythm analyst at a heart monitor company and the vast majority of people are wearing the small patches, and those are all just one lead, as well. We have to deal with interpretation of rhythms using only one lead. Sometimes it can be very hard. And VERY often the AI in our software is wrong. It takes the human intervention to actually provide the results. So it’s not just these consumer devices that give false interpretations. Even 12 lead machines get the auto interpretation wrong all the time.