The Apple Heart Study received great fanfare at least year's American Heart Association meeting and was . Many Apple Watch 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 , most significantly false positive notifications. Recent patient experiences have, in addition, made me concerned about false negative notifications and a lack of sensitivity.
Apple Watch ECG is inherently limited in diagnosing AF above 120 beats per minute (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 Apple Watch had registered high heart rates, sometimes up to 150 BPM, which lasted for several hours.
Although the Apple Watch 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 Apple Watch, and the results came back inconclusive.
Based on the combination of an absence of any irregular heart rate or AF warnings from his Apple Watch and the absence of a diagnosis of AF when he made Apple Watch ECG recordings of the fast rates, the patient assumed that he did not have AF.
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 Apple Watch was able to analyze and make the diagnosis.
The inability of Apple Watch ECG to diagnose AF when the rate is over 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 Apple Watch may be providing many patients who have atrial fibrillation with a false sense of security.
Kardia ECG Accurate >120 BPM
(both the single lead and the versions), on the other hand, has no problems identifying AF above 120 BPM. I have found that the Kardia ECG was highly accurate in patients with rapid AF from using the device in hundreds of my patients since 2013.
After writing about the Apple Watch AF flaw, I opened my that connects to the online ECG recordings each of my patients has made.
Two of my patients with paroxysmal AF had gone into AF in the last 2 days and made recordings.
Both of them had rates over 120 BPM. In both cases, Kardia had easily made the diagnosis. Apple Watch would have declared these "inconclusive."
Patients should be aware of this Apple Watch AF flaw. The absence of a declaration of possible AF on the Apple Watch ECG should not reassure anyone of the absence of AF.
Apple Watch users should have their high rate recordings reviewed by a cardiologist. Alternatively, they could purchase a Kardia device and utilize it for heart rates over 120 BPM.
I have received no payment -- monetary or otherwise -- from AliveCor (Kardia's manufacturer), nor do I own any of its stock.
is a private practice noninvasive cardiologist and medical director of echocardiography at St. Luke's Hospital in St. Louis. He blogs on nutrition, cardiac testing, quackery, and other things worthy of skepticism at where a version of this post first appeared.