The Apple Heart Study received great fanfare at least year’s AHA meetings and was subsequently published in the NEJM. Many Apple Watch (AW) wearers having heard of this study may have concluded the device will reliably identify atrial fibrillation (AF).
In my commentary on the Apple Heart Study I pointed out several issues with relying on Apple Watch for AF diagnosis, most significantly false positive notifications. Recent patient experiences have, in addition, made me concerned about false negative notifications and a lack of sensitivity.
AW ECG is inherently limited in diagnosing AF above 120 BPM. This guarantees a substantial number (possibly the majority) of AF episodes will not be recognized. Such false negative notifications may falsely reassure patients that they don’t have AF and delay them seeking medical attention.
Recently, I saw a patient who was referred to me for an abnormal 12-lead ECG. While reviewing his symptoms we discovered that his AW had registered high heart rates, sometimes up to 150 beats per minute, which lasted for several hours.
Although the AW had recorded this high heart rate it had not notified him of the possibility that he had atrial fibrillation or even that he had a high heart rate.
He had made the ECG recording below using the AW and the results came back inconclusive.
The AW ECG recording clearly shows atrial fibrillation going at a rapid rate-over 150 beats per minute-but the accompanying interpretation gives no hint that the patient had AF.
Based on the combination of an absence of any irregular heart rate/AF warnings from his AW and the absence of a diagnosis of AF when he made AW ECG recordings of the fast rates the patient assumed that he did not have atrial fibrillation.
Why is this? Apparently Apple has decided not to check for AF if the heart rate is over 120 BPM.
Given that most patients with new-onset AF will have heart rates over 120 BPM (assuming they are not on a rate slowing drug like a beta-blocker) it appears likely that Apple Watch ECG will fail to diagnose most cases of AF.
I asked my patient to record an ECG with his watch every time he felt his heart racing after our office visit. A few days later he was sitting in an easy chair after Thanksgiving watching TV and had another spell of racing heart. This time the heart rate was less than 120 BPM and the AW was able to analyze and make the diagnosis.
The inability of AW ECG to diagnose AF when the rate is >120 BPM further adds to my concerns about widespread unsupervised use of the device. When we combine inconclusive high heart rate analyses with the unknown sensitivity of the irregular heartbeat notification algorithm the AW may be providing many patients who have atrial fibrillation with a false sense of security.