Ben Lovejoy
A medical review has shown that Apple Watch heart attack detection is
technically feasible using nothing more than the ECG sensors built into
current models.
While Apple's recommended method of taking an ECG reading results in a
1-lead reading, it is possible to apply a different method to obtain a
9-lead read.
There are, however, important provisos to this health news .
Background
Apple first added an electrocardiogram (ECG) feature to the Apple Watch
Series 4, back in 2018. Legal clearances meant that the feature took time to
roll out from the US to other countries - the feature is currently available
in the US, UK, Canada, Australia, Brazil, Portugal, Saudi Arabia, Japan, and
Mexico.
Apple was careful to warn that the ECG feature cannot detect heart attacks
(technically known as myocardial infarction, or MI). This warning is
displayed when you take an ECG reading:
block quote
Note: Apple Watch never checks for heart attacks.
block quote end
And again when the results are given:
block quote
Apple Watch cannot check for signs of a heart attack. If you believe you are
having a medical emergency, call emergency services.
block quote end
The gold standard ECG reading to detect a heart attack is a 12-lead reading.
This compares to the 1-lead reading you get from using the method
recommended by Apple.
However, a medical review shows that the existing sensors can provide a
9-lead reading if the Watch is placed at a series of different locations on
your body.
The Texas Heart Institute Journal reports on a meta review of a significant
number of studies on use of the Apple Watch.
block quote
In the clinical setting, a 12-lead ECG is currently needed to diagnose MI.
Many studies have examined the possibility of using the Apple Watch to
record multiple leads to meet this requirement for a clinical diagnosis of
MI.
Electrocardiographic leads I, II, and III are an integral part of the
standard 12-lead ECG in routine clinical applications. The Apple Watch can
record lead I, and, according to the Einthoven triangle, it could acquire
leads II and III by using different parts of the body.
The watch could be placed on the left lower abdomen, the left thigh, or the
left ankle, and lead II could be recorded by placing the right index finger
on the crown of the watch; lead III could be recorded in the same manner by
placing the left index finger on the crown. The left lower abdomen has been
shown to provide the best quality signal.
Several studies have verified the overall accuracy of this approach and its
comparability to the standard 12-lead ECG, and they have shown the signal's
tracing quality and the duration and amplitude of waves generated by the
Apple Watch to be suitable for diagnosis.
Cardiologists have been able to correctly allocate in blinded fashion more
than 90% of Apple Watch ECG signals to the corresponding standard ECG leads.
These results suggest that the recording of leads I through III by the Apple
Watch is accurate and highly comparable to their recording on a standard ECG
[.]
In the most extensive study to date,21 Spaccarotella and colleagues
enrolled 100 patients, including 54 patients with [MI] and 27 with non-[MI].
In that study, Apple Watch had a sensitivity of 93% and specificity of 95%
for detecting [MI], compared with a sensitivity of 94% and specificity of
92% for detecting non-[MI].
block quote end
Cautions
The paper does contain a number of cautionary notes. First, by virtue of the
fact that you need patients who are experiencing a heart attack at the time
of the study, samples are small.
Second, the heart attack detection criteria may need to be adjusted to take
account of the differences between this and a conventional 12-lead reading -
including the fact that the Apple Watch can only take sequential readings,
not simultaneous ones.
Finally, taking the readings is not easy for someone who is not medically
trained, given the need to take nine readings from specific places on the
body.
It's suggested that a 3- or 4-lead recording may generate reliable results
with less room for user error.
9to5Mac's Take: Apple Watch heart attack detection
At first glance, the idea of using an Apple Watch in this way to confirm a
heart attack may seem crazy. If there is any suspicion of heart attack, you
should immediately call for emergency medical assistance.
However, many people do not do this. They either dismiss chest pain as
something minor, like indigestion, or they decide to wait and see whether it
gets worse. This failure to get immediate help can mean the difference
between life and death. In these cases, a check using the Apple Watch could
well persuade people that they do need to call 911.
The paper is understandably cautious. In particular, the idea that an
untrained user could take nine readings in specific locations is quite a
stretch, especially at a time when you or someone close to you are concerned
that you may be having a heart attack.
Additionally, there are huge regulatory barriers to be overcome before this
type of capability could be promoted by Apple - and equally great legal
risks if the company chooses to do so.
For all these reasons, we wouldn't expect to see Apple Watch heart attack
detection mentioned in an Apple keynote any time soon!
However, it's still impressive to see what is technically possible, and it's
an encouraging step toward a future when heart attack victims can get
confirmation that, yes, you need to call an ambulance now.
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