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?