Putting The Apple Watch 4 ECG To The Test In Atrial Fibrillation: An Informal Comparison To Kardia

My first patient this morning, a delightful tech-savvy septagenarian with persistent atrial fibrillation told me she had been monitoring her rhythm for the last few days using her Apple Watch 4’s built in ECG device.

Previously she had been using what I consider the Gold Standard for personal ECG monitoring- AliveCor’s Kardia Mobile ECG   and I monitored her recordings through our Kardia Pro connection.

I had been eagerly awaiting Apple’s roll out since I purchased the AW4 in September (see here) and between patients this morning I down-loaded and installed the required iPhone and Watch upgrades and began making AW4 recordings.

Through the day I tried the AW4 and the Kardia on patients in my office.

Apple Watch 4 ECG Is Easy and Straightforward

The AW4 ECG recording process is very easy and straightforward. Upon opening the watch app you are prompted to open the health app on your iPhone to allow connection to the Watch ECG information. After this, to initiate a recording simply open the Watch ECG app and hold your finger on the crown.

Immediately a red ECG tracing begins along with a 30 second countdown.

Helpful advice to pass the time appears below the timer:

“Try Not to move your arms.”


“Apple Watch never checks for heart attacks.”

When finished you will see what I and my patient (who mostly stays in sinus rhythm with the aid of flecainide) saw-a declaration of normality:

Later in the day I had a few patients with permanent  atrial fibrillation put on my watch.

This seventy-something farmer from Bowling Green, Missouri was easily able to make a very good ECG recording with minimal instruction





The AW4 nailed the diagnosis as atrial fibrillation.

We also recorded a Kardia device ECG on him and with a little more instruction the device also diagnosed atrial fibrillation



After you’ve made an AW4 recording you can view the PDF of the ECG in the Health app on your iPhone where all of your ECGs are stored. The PDF can be exported to email (to your doctor) or other apps.

ECG of the Bowling Green farmer. I am not in afib.


Apple Watch Often “Inconclusive”

The AW4 could not diagnose another patient with permanent atrial fibrillation and judged the recording “inconclusive”

The Kardia device and algorithm despite a fairly noisy tracing was able to correctly diagnose atrial fibrillation in this same patient.



I put the AW4 on Sandy, our outstanding echo tech at Winghaven who is known to have a left bundle branch block but remains in normal rhythm and obtained this inconclusive report .





Kardia, on the other hand got the diagnosis correctly:





One Bizarre Tracing by the AW4

In another patient , an 87 year old lady with a totally normal recording by the Kardia device, the AW4 yielded a bizarre tracing which resembled ventricular tachycardia:

Despite adjustments to her finger position and watch position, I could not obtain a reasonble tracing with the AW4.

The Kardia tracing is fine, no artifact whatsoever.










What can we conclude after today’s adventures with the Apple Watch ECG?

This is an amazingly easy, convenient and straightforward method for recording a single channel ECG.

I love the idea that I can record an ECG whereverI am with minimal fuss. Since I wear my AW4 almost all the time I don’t have to think about bringing a device with me (although for a while I had the Kardia attached to iPhone case that ultimately became cumbersome.)

Based on my limited sample size today, however, the AW4 has a high rate of being uncertain about diagnoses. Only 2/3 cases of permanent atrial fibrillation were identified (compared to 3/3 for the Kardia) and only 4/6 cases of sinus rhythm were identified.

If those numbers hold up with larger numbers, the AW4 is inferior to the Kardia ECG device.

I’d rather see the AW4 declare inconclusive than to declare atrial fibrillation when it’s not present but this lack of certainty detracts from its value.

What caused the bizarre artifact and inconclusive AW4 tracing in my patient is unclear. If anybody has an answer, let me know.

We definitely need more data and more studies on the overall sensitivity and specificity of the AW4 and hopefully these will be rapidly forthcoming.

For most of my patients the advantages of the AW4 (assuming they don’t already have one) will be outweighed by its much greater cost and we will continue to primarily utilize the Kardia device which will also allow me to view all of their recordings instantaneously in the cloud.

Conclusively Yours,


5 thoughts on “Putting The Apple Watch 4 ECG To The Test In Atrial Fibrillation: An Informal Comparison To Kardia”

  1. Interesting. I have been using the Kardia band on my apple 3 watch for a year and paid for the premium plan as well. I ordered the new Apple Watch 4 today, since the app is finally out. I found the Kardia very helpful until I began Tikosyn. I have frequent PACs which seems to confuse the reading now, as my EP tells me I am in normal rhythm, and While I often don’t feel normal, I can tell the difference, but Kardia says possible afib or unclassified.

    I am grateful for the Kardia till now….not one useless hospital ER, despite some rough months. Between Kardia,my doctor, and my own calm monitoring I knew when I was NOT in trouble.

    I had hoped the apple watch4 would be better but your testing is discouraging. However, with trade in on my A watch3, and the cancellation of my monthly $9.99 charge for the Kardia Premium, I feel it will not really be more expensive. (And my vanity has finally been served. i can go back to stylish watch bands. 🤷‍♀️) My pleas to Kardia went unnoticed.

    I have appreciated your reporting and it has informed my decisions on these devices.

  2. This and your prior comments about the Kardia product and Apple watch seem consistent with the possibility that you are a paid “consultant” to AliveCor. Although I appreciate your experience, if you have any ties to the Kardia product this should be revealed, and if not, please state so.
    JCM, MD

    1. Dr. Moore,
      I’m glad you brought this up.
      My previous post about Kardia Pro was very positive but if you look at all I’ve written about Kardia and AliveCor over the last 5 years you will see it is very balanced and often points out inaccuracies of the device. Because my post on KardiaPro eliminating need for long term monitors was so positive I posted the following at the end of it.

      N.B. I realize this post appears to be an unmitigated enthusiastic endorsement of a commercial product which is quite uncharacteristic for the skeptical cardiologist.

      One might wonder if the skepcard is somehow biased or compensated for his endorsement of Kardia.

      In all honesty, this sprung from my love of the device’s improvement in my afib management and I have received no payment, monetary or otherwise from AliveCor and I own none of their stock (and I’m not even sure if it is on the stock market.)

      This statement is still true and I still don’t know if Alivecor is listed on the stock market.

  3. Feedback on Apple Watch Kardia Smart Rhythm app would be appreciated. Especially in comparison to the Apple Watch 4 Heart app.

    When Kardia Smart Rhythm is running on my Apple Watch 3 the movement monitoring functions are shut down.

    So the watch is now dedicated to solely monitoring heart rhythm.

    It seems to me that notifications via the Smart Rhythm app are more accurate than the native Apple Heart app, but I think that with the Apple app the activity monitoring is unaffected.

    I have the Kardia Bluetooth device attached to my iphone, but will soon get a Kardia band for the watch.

    Thanks for these posts – very interesting and much appreciated.

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