The truth of ECG on Apple Watch 4: FDA Approval, Heart Attack, Atrial Fibrillation

Find the truth behind Apple Watch 4's ECG, Atrial Fibrillation notification and FDA approval

During the Apple Event on 12th September, Apple announced Apple Watch 4. The Watch 4 can take ECGs on the go in just 30 seconds with just your finger on the Digital Crown apart from detecting a fall and calling Emergency services. The main thing though that piqued the medical world’s interest was the ECG feature. In a recent post on Reddit, an Emergency Physician explained the truth of Apple Watch’s ECG feature. He also talked about the FDA Approval Apple Watch 4 got.

Apple Watch ECG vs Machine ECG

This is one of the first things the Doctor explained. A normal ECG in a hospital contains 10 electrodes attached to different parts of your body. These 10 electrodes form 12 leads which gives Doctors a 3D view of the heart. Conventionally, ECG relies on the principle of power gradients, i.e., movement from the negative (-) pole to the positive (+) pole.

The P Wave

A normal ECG has P wave, QRS complex and T wave
Normal ECG and components

The diagram above shows a normal ECG. The P wave (the first upward bump) indicates Atrial contraction or Atrial systole. P wave is formed when your atrium contracts itself to pass the blood to ventricles. Lead I generally measures P wave. And, Lead I is measured across the right arm and left arm on a conventional ECG machine.

It’s really hard to explain everything about ECG in this article, but if you are interested you can watch the following video, for starters:-

Now, an ECG needs atleast two electrode points. And, multiple such electrodes help us understand the heart in all dimensions. But, as you know, for the ECG part, the Apple Watch 4 has one electrode on the Digital Crown which your fingertip touches while taking an ECG. And, I assume the other electrode is on the back of the watch (to be clarified). Assuming my two electrode theory of the Apple Watch 4 is true, if you wear the Watch on your left hand wrist, the electrode on the back of the Watch is the LA (left arm) electrode. Now, naturally your right index finger will touch the other electrode on the Digital Crown, unless you have supernatural flexibility. This will be the RA (right arm) electrode.

So, the ECG you get with the Apple Watch looks at the heart in only one dimension. If you are a Doctor, the Apple Watch ECG is what you get when you use only two electrodes – RA and LA to gather only Lead I. Lead I can measure the P wave almost satisfactorily but, Lead I can’t visualise QRS complex and T wave properly.

Can Apple Watch 4 detect Heart Attack?

The most logical answer to that question, in most cases would be “No!” Let me explain why. Most Doctors refer to the T wave to look for clues of a previous Myocardial Infarction (Heart Attack). The T wave is usually inverted in a patient who has had a heart attack before. Also, in cases of an impending heart attack, you can find irregularities in the T wave.

Since Apple Watch 4 with a single lead can’t output the T wave properly, such an ECG might not be efficient to study heart attacks. The Reddit physician says, even some ECG machines at times, miss heart attacks.

FDA Approval

The Physician also linked to the actual FDA Letters for the Apple Watch. You can find them here and here. Apple applied for FDA approval for two of Apple Watch 4’s features:-

  1. ECG
  2. Atrial Fibrillation (AFib) Notification

Apple said, these features were approved by FDA. But, this doesn’t make Apple Watch 4 an FDA approved Medical device. To explain further, here’s what the FDA letter said about the ECG on the smartwatch:-

The ECG app is intended for over-the-counter (OTC)use. The ECG data displayed by the ECG app is intended for informational use only. The user is not intended to interpret or take clinical action based on the device output without consultation of a qualified healthcare professional. The ECG waveform is meant to supplement rhythm classification for the purposes of discriminating AFib from normal sinus rhythm and not intended to replace traditional methods of diagnosis or treatment.

About the Atrial Fibrillation Notification feature, the letter said:-

The feature analyzes pulse rate data to identify episodes of irregular heart rhythms suggestive of atrial fibrillation (AFib) and provides a notification to the user.The feature is intended for over-the-counter (OTC) use. It is not intended to provide a notification on every episode of irregular rhythm suggestive of AFib and the absence of a notification is not intended to indicate no disease process is present; rather the feature is intended to opportunistically surface a notification of possible AFib when sufficient data are available for analysis. These data are only captured when the user is still.

Apple Watch 4: What it can do and what it can’t

So, here’s a few things you need to know about FDA approval for ECG and AFib feature on the ECG watch:-

  • Apple Watch 4, as a device has been classified under Class II (same as condoms, home pregnancy kits, etc).
  • ECG and AFib App on the Watch should be used by people only above 22 years of age.
  • You have to talk to a qualified medical personnel before taking any action based on data collected by the watch.
  • The AFib feature only works if the user is still.
  • The features are intended for use over-the-counter (OTC) only.
  • Apple Watch 4 can’t detect heart attacks exclusively.
  • Apple Watch 4 is not ideal or indicated for people who have already been diagnosed with AFib. Such people should see a physician regularly.


If you saw the event, Apple mentioned FDA approval, but didn’t mention the FDA class of the device. Moreover, though they talked about the ECG feature, they never even mentioned Heart Attack. Actually, we can’t blame Apple for the wrong concepts we have, of the Apple Watch 4’s heart diagnostic features. This article is to clear up everything about these features.

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