ACC 2019 preview – Detection vs diagnosis: Irhythm and the Apple Watch

Will the Apple Heart Study allow early detection of arrhythmias, or drive the worried well to doctors unnecessarily? For Irhythm Technologies, either is a good outcome.

At the upcoming meeting of the American College of Cardiology the first session examining late-breaking clinical data will be devoted entirely to a single trial: the 420,000-strong Apple Heart Study. This looks at the ability of the Apple Watch to screen healthy people for atrial fibrillation, but there are doubts about the utility of such an approach, not least because it could risk overdiagnosis. The way the trial has been designed is also somewhat questionable.

If the trial does show the Apple Watch to be reasonably accurate at detecting the condition, another company stands to benefit from its increased use as an arrhythmia screen: Irhythm Technologies makes a cardiac monitor, called Zio, that could be used to confirm or rule out AF after detection by Apple’s device. 

“With any broad consumer-based screener there’s a question of, how accurate is it?” says Derrick Sung, executive vice-president of strategy and corporate development at Irhythm. He admits that the cardiology community will be concerned with the trial’s false positive rate, and about whether the Apple Watch could be alerting patients unnecessarily.

But it will take monitors like Irhythm's Zio to determine whether these positives are in fact false – so Zio sales could increase either way.

Irhythm's Zio XT heart monitor patch
Irhythm's Zio XT heart monitor patch.

Apple of discord

The primary endpoints of the Apple Heart Study, both of which concern only participants aged over 65, are worth looking at closely. The first involves the detection of AF using an ambulatory ECG monitor patch in participants who had previously received an irregular pulse notification on their watch. 

But the trial’s protocol does not specify a target level of concordance, so when the figure is presented on Saturday it will be up to cardiologists to determine whether it is meaningful. 

The second primary endpoint looks at AF detection simultaneously by watch and patch. The threshold for a hit here is specified: if AF detected by the watch is confirmed in 75% of cases this will be considered clinically meaningful. In other words, a quarter of the alerts being false positives is acceptable in the eyes of the trial’s designers. 

It will be acceptable to Irhythm as well. Mr Sung says the company has heard anecdotes of patients coming in with notifications from their Apple Watch and then being prescribed the Zio device. “That’s a very natural expectation for how this will play out in the marketplace, assuming that the Apple Watch is successful and works as advertised,” he says.

Apples and oranges

Zio is entirely different from the kind of consumer engagement approach to digital health Apple is pursuing. The patch is worn on the patient’s chest for three to 14 days, during which it makes more sophisticated determinations than the Apple Watch is capable of.

“It’s a prescription-only diagnostic that provides a definitive diagnosis of all 12 classes of arrhythmia – not just AF but ventricular tachycardia, atrioventricular block, supraventricular tachycardia,” Mr Sung says. 

After the wear period is up, the patient removes the patch and posts it to Irhythm. The company extracts the data and sends them on to the patient’s doctor, who makes a diagnosis and prescribes treatment. The patient never sees their own data.

Irhythm is not the only one in this space: Biotelemetry provided the Epatch used in the Apple study, and Bardydx has developed the Carnation ambulatory monitor. Meanwhile, larger legacy devices, Holter monitors, have been used for heart monitoring for years.

Irhythm is making moves into screening for asymptomatic AF in high-risk populations. Last year, data from the mSToPS study showed that Zio improved diagnosis rates.

This is the kind of population that could be better reached if the Apple Heart Study is considered a success. “Wider use of the Apple Watch could drive awareness of arrhythmias in a broader population that certainly we wouldn’t be able to reach being prescription-only,” says Mr Sung.

Harder endpoints

Still, AF is not dangerous in itself, directly causing little more than fainting, shortness of breath and chest pain. The real concern with the condition is that it is a risk factor for other disorders, most notably stroke. So far no trials have assessed the ability of consumer wearables with heart rate monitors to prevent strokes. 

“Would it be more beneficial to be able to show an actual clinical outcome – that by detecting an arrhythmia they could actually ultimately reduce stroke rate? Of course,” says Mr Sung. Currently, he says, there is an assumption that detecting and treating AF can reduce stroke rate. 

If cardiologists are impressed by Apple’s data on Sunday that will be a start – and great news for Irhythm – but more trials with harder endpoints would be ideal. 

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