Wed. Nov 30th, 2022
Image of a heart track with irregular activity.
enlarge / See that erratic up-and-down movement right before the big beat? That’s atrial fibrillation.

What is atrial fibrillation and why did Apple decide it’s worth screening for it? The first question is much easier to answer, so let’s get that out of the way.

Your heart has four chambers, two atria and two ventricles. The atria are smaller chambers at the top of the heart, and their contraction fills the larger ventricles with blood. The ventricles then provide the powerful push that sends the blood to the lungs to take up oxygen or to the body once it is oxygenated.

Don’t have a rhythm

The correct coordination of the beating of all these parts requires a carefully synchronized propagation of electrical signals throughout the four chambers. Given the complexity of getting this to work, it’s not surprising that things sometimes go wrong. The cause of problems can be anything from a temporary physical change to a permanent problem with your heart’s development that started when you were an embryo. The consequences can range from irrelevant to fatal.

For example, a common problem is a premature contraction, either caused by the atria (premature atrial contractions, or PACs) or the ventricles (PVCs). In PACs, the beat looks completely normal when the electrical track is checked – it just happens sooner than the normal rhythm would dictate. Since the beats are normal, PACs by themselves are not a health threat. However, they can sometimes be caused by serious underlying issues so it is often worth checking them out if they are noticed.

PVCs result in an altered heart rate but are not considered a problem as long as they are sufficiently rare. If several occur in quick succession, they can cause serious problems. Therefore, they should always be checked out.

There are also a number of arrhythmias where the electrical activity of the heart is not normal; the most common of these are fibrillations. In this case, the electrical impulses are disorganized and distributed irregularly throughout the rooms. Instead of contracting in a smooth wave, the ventricles of the heart cramp and don’t generate a solid contraction.

Since the ventricles keep blood flowing throughout the body, ventricular fibrillation is fatal. It doesn’t make much sense to screen for that.

Which brings us to atrial fibrillation, or a-fib. To simplify, this is the spasms of the upper chambers, often accompanied by an irregular and often rapid heartbeat. While the atria help the heart work properly, the ventricles alone are enough to supply the body with blood. So a-fib poses no direct health risk. But it produces a variety of long-term effects.

Increased risk

A-fib has a risk because when the atria cramp instead of contracting, it gives blood a chance to build up in it, outside the main circulatory system. If left in the same place long enough, some of this blood will form small clots that are eventually pushed out of the heart and into the general circulation. These clots can cause immediate problems, such as heart attacks or strokes — a-fib greatly increases the risks of each.

But the small clots can also cause subclinical problems, damaging parts of the heart without causing obvious symptoms. In another example, patients with a-fib have an increased risk of early-onset dementia due to multiple small clots that were not substantial enough to cause stroke symptoms.

Aside from the long-term health risks of a-fib, there are a number of other things that make Apple’s decision to screen for it reasonable. The first is that the problem can be treated in several ways. We have many drugs that alter the heart rhythm, and in some people block or limit this a-fib. You can also treat the problematic symptom, blood clots, by taking blood thinners. Finally, there are surgical procedures that completely eliminate a-fib in some individuals. A diagnosis can mean protection against the worst consequences.

A-fib detection is challenging simply because there are some people whose arrhythmias are asymptomatic or sporadic. I have experienced both a-fib and PACs, and I can actually feel when my heart is out of rhythm and feel the difference between the two arrhythmias. But many people can’t, and they would never know they were at risk for treatable problems if the arrhythmia went undetected during regular screening.

Sporadic and asymptomatic arrhythmias can complicate monitoring and diagnosis. And diagnosis is important for people who can feel their heart go out of rhythm — they know they have an arrhythmia and don’t need to be screened — but don’t know what arrhythmia it’s shifting to. A diagnosis requires a record of the heart’s activity while it is out of rhythm, which can be difficult to control when the arrhythmia is sporadic.

Monitoring the arrhythmia is important for people taking drug treatments because sometimes the drugs can lose their effectiveness and the patients don’t know it. The sporadic occurrence of the arrhythmia means that it is a matter of chance whether it would appear during monitoring. In my case, I get a sporadic mix of PACs and a-fib, and monitoring helps determine if I’m experiencing the more dangerous of the two more often.

So there are really two separate issues that the Apple Watch can now address: screening and monitoring.

In addition to the optical heart rate monitor, the bottom of the Apple Watch Series 4 has an electrode circle for measuring ECG readings.
enlarge / In addition to the optical heart rate monitor, the bottom of the Apple Watch Series 4 has an electrode circle for measuring ECG readings.

Valentina Palladino


Screening is the application for which Apple has received FDA approval, and there is certainly value in that. Effective treatment of a-fib has been shown to reduce long-term consequences, and those long-term consequences have significant costs, both in terms of patient quality of life and the cost of the health care they require. . Since there are few known risk factors for a-fib in healthy populations, it may just be a coincidence that it is picked up during screening.

But the data Apple provided to the FDA showed that there were false positives and negatives. False negatives mean that some people with a-fib are not detected by the watch. That may be unfortunate for them personally, but it won’t leave them in worse shape than they probably would have been before. Hopefully, doctors won’t take the watch’s word and stop doing additional screening.

The bigger problem may be false positives. Even if these turn out to be very rare, sales estimates indicate Apple shifts about 20 million watches a year. At a false positive rate of two percent, that could mean more than 400,000 people want to talk to their cardiologists about a-fib next year. There is also the issue of instances where the a-fib is real, but irrelevant. We really don’t know how often people experience a short bout of arrhythmia and then stay in the normal rhythm for years. But we do know that a-fib is the most common outcome of what’s called “holiday heart” (or sometimes “Friday night heart”), a temporary arrhythmia caused by excessive drinking in otherwise healthy people.

All this suggests that mass screening via watch can have good and bad points. It’s great for those who have a-fib but are asymptomatic or only suffer from it sporadically. Identifying and treating it will be positive. But we can also see it identify many patients with false diagnoses, or who have some extremely rare bursts of arrhythmia. That can affect them emotionally and potentially overload our heart care system.

Monitoring and diagnosis

Ironically, it’s the programs Apple didn’t ask permission for—monitoring and diagnostics—that could be used more wisely. Currently, the standard way to deal with both is the regular use of what’s called a Holter monitor, essentially a portable version of the EKG machine. That device generates traces of the heart’s activity, as shown above, and it has become increasingly sophisticated, as it can be applied as a single patch or connected to a cell phone as a Bluetooth device. But Holters have some limitations. If the arrhythmia is sporadic, there is no guarantee that the monitoring will coincide with the appearance. The monitor can also be uncomfortable and difficult to sleep with – for example, I have developed an allergy to the adhesive on the electrodes.

Due to the erratic nature of my arrhythmias and because they are symptomatic, both screening and monitoring may benefit from a high quality personal heart monitor. My arrhythmia only showed up on the Holter monitor briefly for a week, so it was difficult to diagnose until I happened to have an episode while near my doctor’s office and came in for an EKG. A watch could have greatly simplified the process.

For monitoring, my cardiologist and I switched to a small Bluetooth device that extracts the heart rate when your fingers are placed on it. Now, instead of hoping to be on the Holter when arrhythmias hit, I just record it and email it to my doctor from my phone whenever I have a case of arrhythmia. If the watch’s ECG function worked equally well, it could easily replace this device for any of these needs.

Since the watch also detects the onset of a-fib, this feature can be easily integrated into the software. Provide an alert suggesting the user to take an EKG when the system detects possible a-fib in the background. While the quality of a Holter monitor will likely be better, it may not be necessary to determine when a person’s heart is examined more closely.

For whatever reason, Apple has chosen not to go down this road, at least for now. That decision may be wise. Their first iteration of the hardware and software will be a public health experiment, the magnitude of which makes it exceptional. It’s probably a good thing to look closely at the results before proceeding.

Corrections: Fixed a typo in the false positive discussion and edited the PVC discussion.

By akfire1

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