What is atrial fibrillation and why is your watch talking to you about it?

What is atrial fibrillation, and why did Apple decide that it was worth it to be examined? The first question is much easier to answer, so remove it.

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 blood to the lungs to suck oxygen or to the body once it is oxygenated.

No rhythm

The proper coordination of the beat of all these parts requires a carefully synchronized diffusion of the electrical signals through the four chambers. Given the complexity of implementation, it should not be surprising that this happens sometimes. Blame for problems can be a temporary physical change to an ongoing problem with the development of your heart that began when you were an embryo. The consequences can range from irrelevant to fatal.

For example, a common problem is premature contraction, triggered by the atria (premature atrial contractions or PAC) or the ventricles (PVC). In this case, the beat will look perfectly normal when its electrical trace is checked – it just happens earlier than the normal rhythm would dictate it. As the beats are normal, PAC and PVC do not pose a threat to health. However, they can sometimes be triggered by serious underlying issues. It is therefore often useful to check them when they are detected.

There are also a number of arrhythmias in which the electrical activity of the heart is not normal. the most common are fibrillations. In this case, the electrical pulses are disorganized and unevenly distributed in the chambers. Rather than contracting a smooth wave, the chambers of the heart contract and do not generate a solid contraction.

Since the ventricles feed the blood through the body, ventricular fibrillation is fatal. Not much to filter for that.

Which brings us to atrial fibrillation, or a-fib. For simplicity, it is an irregular and often rapid heartbeat. While the atria help the heart function properly, the ventricles alone are enough to keep the body in blood. So, a-fib does not create an immediate risk to health. But this poses long-term problems.

Increased risk

A-fib is at risk because, when the atria contract rather than contract, the blood is allowed to cluster outside the main circulation. Left in the same place long enough, some of this blood will form small clots that will eventually be expelled from the heart and enter the general circulation. These clots can cause immediate problems, such as heart attacks or strokes – the a-fib greatly increases everyone's risk.

But small clots can also cause subclinical problems, damaging parts of the heart without causing overt symptoms. In another example, patients with atrial fibrillation have an increased risk of early onset dementia of multiple small clots that were not large enough to trigger symptoms of stroke.

Aside from its long-term health risks posed by a-fib, there are two other factors that make Apple's decision reasonable. The first is that the problem can be addressed in various ways. We have a lot of medications that change the heart rate and, in some people, they block or limit atrial fibrillation. You can also treat the problematic symptom, blood clots, using anticoagulants. Finally, there are surgical procedures that, in some individuals, completely eliminate the a-fib. Thus, a diagnosis can mean protection against the worst of consequences.

The detection of fibromyalgia is a challenge simply because some people are asymptomatic or sporadic. I have experienced both a-fib and PAC, and I can actually feel whenever my heart is out of sync and feel the difference between the two arrhythmias. But many people can not and they would never know that they might suffer from treatable problems if the arrhythmia was not detected during regular screening.

Sporadic and asymptomatic arrhythmias can make surveillance and diagnosis difficult. And the diagnosis is important for people who can feel their heart become unbalanced – they know that they have arrhythmia and that they should not be detected – but do not know what arrhythmia they are moving. A diagnosis requires a record of heart activity while it is not rhythmic, which can be difficult to arrange when the arrhythmia is sporadic.

Arrhythmia monitoring is important for people who use drug treatments because medications can sometimes lose their effectiveness and patients have no way of knowing. The sporadic occurrence of arrhythmia means that it is very likely that it will appear during monitoring. In my case, I get a sporadic mix of PAC and a-fib, and monitoring helps determine if I feel the most danger from both more often.

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

Screening

Filtering is the application where Apple has received authorization from the FDA, and there is certainly value to that. It has been demonstrated that effective treatment of the a-fib can reduce the long-term consequences and that its long-term consequences entail significant costs, both on the quality of life of the patients and on the patients. health care costs they need. Since there are few known risk factors for fibrin in healthy populations, having it taken during screening can be a matter of luck.

But the data that Apple submitted to the FDA showed that there were false positives and negatives. False negatives mean that some people with fib will not be detected by the watch. This may be unfortunate for them personally, but it will not leave them worse off than they probably would have been before. If all is well, doctors will not accept the watchword on things and will stop performing additional screenings.

The biggest problem could be false positives. Even though these have proven very rare, sales estimates indicate that Apple could move about 20 million watches a year. With a two percent false positive rate, this could mean that over 200,000 people will want to talk to their cardiologists about af-fib next year. There is also the question of where the a-fib is real but of no consequence. We really do not know how often people can experience a short period of arrhythmia and then stay in a normal rhythm for years afterwards. But we know that the a-fib is the most common result of what is called the "holiday heart" (or sometimes the "heart of Friday night"), a temporary arrhythmia caused by a consuming excessive alcohol in healthy people.

All of this suggests that mass watch-based screening can have both good and bad points. It's great for those who have an a-fib but are asymptomatic or suffer it only sporadically. Their identification and treatment will be positive. But we can also see that he identifies many patients with false diagnoses, or who have some extremely rare arrhythmias. It can affect them emotionally and potentially overload our cardiac care system.

Follow-up and diagnosis

Ironically, these are not the applications for which Apple has not asked permission – monitoring and diagnosis – that could make use cases more wisely. Currently, the standard way of dealing with both of these problems is the regular use of what is called a Holter monitor, essentially a portable version of the ECG device. This generates traces of heart activity like the one shown above. These have become increasingly sophisticated because they can be applied in a single patch or connected to a mobile phone as a Bluetooth device. But Holters have limits. If the arrhythmia is sporadic, there is no guarantee that surveillance will coincide with its onset. The monitor can also be uncomfortable and difficult to sleep – for example, I have developed an allergy to the electrode adhesive.

Because of the irregular nature of my arrhythmias and because they are symptomatic, they could both benefit from a high quality personal heart monitor. The arrhythmia only appeared briefly for a week on the Holter monitor, and so it was difficult to diagnose until I had an episode near my doctor's office and that I go to an ECG. A watch would have greatly simplified this.

For surveillance, my cardiologist and I switched to a small Bluetooth device that extracts heat waves when your fingers are placed there. Now, instead of hoping that I am on the Holter when arrhythmias occur, whenever I have an arrhythmia case, I simply record it and send it out. by email to my doctor. If the ECG function of the watch worked as well, it could easily replace this unit for one or the other of these needs.

Since the watch also detects the appearance of the a-fib, this feature can be easily integrated into the software – issue an alert suggesting the user to take an ECG each time the system in the background detects a possible a-fib. Although the quality of a Holter monitor is probably better, it may not be necessary to determine when someone's heart should be examined more closely.

For whatever reason, Apple has chosen not to follow this path, at least for the moment. This decision may be wise. Their first iteration of hardware and software will be a public health experience, the size of which makes it exceptional. It's probably a good thing to look closely at the results before pushing further.