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Circulation published a nice review this week on the rationale for atrial fibrillation screening: circ.ahajournals.org/content/135/19/1851.full?ijkey=StzSPk8eljGaP2G&keytype=ref

The main reason is that 10% of strokes are associated with undiagnosed atrial fibrillation. The patients who present to the emergency room are a pretty biased sample--for one, they're experiencing symptoms. To prevent strokes, we need to have a way to catch AF in asymptomatic people.

Part of the challenge here is that episodes of atrial fibrillation can be infrequent--in CRYSTAL-AF, for example, it took 84 days from randomization to first episode--and existing monitoring devices like Holters or Zio patches are only worn 24 hours to 2 weeks. The great thing about Apple Watch and other consumer wearables is that they're worn for months or years. That means if we can prove the algorithm is accurate, we can get higher time-coverage than a traditional medical device, catch more AF early, and prevent those 10% of strokes described in the Circulation article.

5 comments

Perhaps it would be more accurate to say "we might catch more AF early, and anticoagulating those people might reduce their risk of debilitating stroke more than we increase their risk of lethal gi bleed or head bleed"?

The issue is whether the af you find through this kind of screening is associated with the same risk of stroke as conventionally diagnosed af - if not, their risk reduction from anticoagulation might not justify the bleeding risk from anticoagulating them.

The linked article suggests it might be "unethical" to even do a trial of anticoagulation vs control in af detected by such screening. That seems like a dangerous position for them to take, particularly coming from a group that is largely funded by the drug companies who sell expensive anticoagulation medication.

I would encourage readers to jump to the "sources of funding" and "disclosures" section of the linked review article to see just how many of the authors receive money from the drug companies.

None of that is a criticism of the authors of the UCSF study, this kind of technology is certainly an area worth exploring. I would just be very wary of the push by drug companies and the doctors paid by them to 1) find asymptomatic conditions 2) call it 'disease' based on older studies of patients who were much sicker 3) 'treat' them with expensive medications for the rest of their lives without actually doing research to see if it would benefit or harm the patient.

actually, the public health risk of stroke in paroxysmal AF is pretty high. Even if the expensive drugs weren't available, we'd still use coumadin which is dirt cheap. The elimination of stroke risk is worth the risk of bleeding complications.

actually, you're assuming that the kinds of patients who were diagnosed with paroxysmal AF in the studies showing increased stroke risk 10 or 20 years ago are going to be similar in risk profile to asymptomatic patients who might now be diagnosed with paroxysmal AF based on some as yet underdetermined time criteria using new technology. To quote the paper: "Alternative arbitrary or data-derived atrial high-rate episodes burden cut points have been explored over the subsequent 10 years, ranging from 5 minutes to 24 hours.11 Uncertainty remains about the minimum burden that increases thromboembolic risk."

On the other hand, there is no uncertainty about the degree of risk from bleeding (small, but present, and occasionally lethal). So yes, patients with paroxysmal AF based on current technology and clinical standards benefit more from reduction in stroke risk than they lose in bleeding risk. That doesn't mean that all patients in the future, with any degree of paroxysmal AF diagnosed using more sensitive technologies will benefit similarly

I think what you are trying to say is that - you think there may be varying "degrees" of PAF and that certain types may be less risky? That is something that certainly can be debated, but at least most of the of thinking so far is that any presence of PAF, aside from isolated episodes after cardiothoracic surgery, carries the same, if similar risk.

I think the way my stroke colleagues look at it, is sort of the other way around - more like PAF is PAF, and as far as they can tell, based on current data, there is relatively few stratification levels that the current medical data can tell us. Meanwhile, the current assumption of risk from PAF, is so high, vs. the risk of anticoagulation (adjusted for individual patient, i.e. maybe not the patients with coagulopathies or risk of falls) that they view NOT anticoagulation as a higher risk. Because if one is wrong about it, the result is paralysis, coma or worse. If there are cheaper ways of detecting AF, all the better.

But overall, anticoagulation decisions aside, think about it - this is a potentially a cheap way to passively screen for the condition in the population. Orders of magnitude so, and possibly w/ more accuracy than a typical holter monitor or even the newer implantable devices (which in all probability use simpler rhythm analysis). Even if you are worried about the potential existence of differing levels of AF, the wealth of new data should go a long way towards further understanding AF and figuring out whether differing levels of risk exist.

Thanks for taking the time to reply, I can now better see how this could be of benefit

Thanks for taking the time to ask that question! This was super interesting.

This is really cool. I have an ICM (Medtronic LINQ) for something I don't believe an iWatch could detect so this isn't an option for me, but I do know they are sometimes used for AF as well, and mine cost over $60,000 to implant (billed to insurance, though my part was still much more than an iWatch costs). I have to think doing the same with an iWatch massively increases the pool of people who are capable of affording continuous monitoring.

I'm in exactly the target market here in the UK. I've had PAF in the past, I suspect it happens at night when I'm asleep, but multiple cardio traces have failed to catch it.

Short of buying my own Holter trace machine ($500, and an inconvenient mess of wires) or having an implant (possible on the NHS, and being considered, but the waiting list is long) there's no way I can be sure if PAF is enough of a problem to justify the lifestyle changes that would be caused by going on anti-coags.

Cheap continual monitoring would be a game changer.

Yeah I've used a Holter a few times they are definitely a pain to sleep in! For certain arrhythmias you need a 6-12 lead EKG though (iWatch wouldn't work in those situations as far as I understand).

Hmm, this makes me think personal insurance will at some point in the not too distant future give hefty premium hikes to those who refuse to wear a 24-7 monitoring device; as vehicle insurance in the UK is doing with monitoring devices (cameras/accelerometer-type devices).

Pretty sure Obamacare wouldn't allow that, but they could start subsidizing devices.

I got an Apple Watch through my company's Health insurance provider, for free.

Hi Brandon-

I can't find good tables in the article or on your teams site. [edited]

I know you guys take your numbers seriously but I'd love to see anything allowed out pre-publication.

[edit]Thanks to poster below I see this is AUC. Thanks!