Apple Watch, Cardiogram, and Atrial Fibrillation

Cardiogram app (iOS, WatchOS).
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Fascinating news today that the app Cardiogram (iOS, WatchOS) has used machine learning algorithms to differentiate between regular cardiac rhythms and irregular rhythms such as atrial fibrillation (AF) from data collected by the Apple Watch. The study in which this finding was presented states the app picked up 97% of AF episodes. While real-world usage may give different results (e.g. if the Apple Watch wasn’t worn correctly), and consumers should be cautioned about false negatives and the risk in trusting any device absolutely – this is still very exciting news.

AF is a key concern in heart disease. The heart is made of four chambers, two atria and two ventricles. Blood normally flows from the atria to the ventricles and from there to the lungs and the rest of the body. For the atria to transfer the blood over to the ventricles, they need to pump well. In AF, the atria do not pump in a coordinated manner and, instead, “fibrillate”. This causes two key problems. First, the ventricles aren’t filled with blood well enough. This means that when the ventricles contract to send blood to the rest of the body, they are pumping out a lesser amount of blood. One of the organs that gets this reduced amount of blood is the brain – and this is why syncope (fainting) or pre-syncope (feeling as if you’re about to faint) can be associated with AF. The other, potentially more serious, issue with AF is that because the blood isn’t moving along from the atria well enough, it increases the likelihood of clots forming in the atria. These clots can be pumped by the heart into circulation and go on to block blood vessels, such as in the brain causing a stroke. There are other reasons why AF is something to take seriously, but this is the gist of it.

For those who are already in known AF, the cornerstone of management is rate control and anticoagulation medication. It would be interesting to see if the Cardiogram app not only recognizes when the patient has gone into AF, but also accurately notes the actual heart rate during the AF event. Atrial fibrillation where the rate is within accepted range, is a completely different beast to “fast AF” which can cause life-threatening hemodynamic compromise (critically inadequate amount of blood pumped to the body). In cases where rhythm control is also a treatment aim (e.g. when the patient experiences troublesome symptoms despite rate control), I wonder if the Cardiogram app could help give an idea of how often the rhythm is irregular. It would also be very helpful if AF detection by the app automatically fired off an alert to caregivers, particularly in the elderly who may not always be able to signal for help immediately.

Another use I can think of for AF detection is when a patient with known AF presents with syncope. In the absence of witnesses to the syncopal event, history of the presenting complaint can be tricky to elicit. This can make it difficult to determine if the syncope was due to AF (poor pumping by the heart), or a different reason. If the Apple Watch showed an AF event coinciding with the syncopal event (perhaps by measuring a sudden drop in altitude?), that could be pretty handy information for the clinicians. I can think of so many great ways to use the sensors on Apple Watch to help with serious medical conditions, but I’ll leave that for a separate blog post.

I feel Apple is well suited to push a wearable into serious healthcare territory, beyond mere step tracking. Building trust will be key but I think Apple could just pull it off.