Apple Watch Versus Kardia to Monitor Atrial Fibrillation From Home: A Case Study

I received an email last week from a patient with paroxysmal atrial fibrillation.

“I am in a fib again. This is from my watch. I also did some reading on Kardia.
I don’t feel it at all.”

The email attachment was a PDF of a single lead ECG rhythm recording she had made after her Apple Watch alerted her that her heart rate was abnormally high.

As she also utilizes Alivecor’s Kardia mobile ECG device and I can view the Kardia recordings through my online dashboard, I logged into Kardia Pro and pulled her chart up. Sure enough, the nice green dots showing sinus rhythm had been replaced by the orange dots of atrial fibrillation (afib.)

This patient takes the antiarrhythmic flecainide twice daily and it had, until recently, done a good job of suppressing the afib for many years. But the chart shows me that earlier in September she had another episode of afib. This episode like her prior afib episodes we treated by having her take an extra dose of flecainide and it resolved several hours later.

By the time I read her email and checked things on KardiaPro she had already taken an extra flecainide and gone back to sinus rhythm. The chart of her Kardia recordings is below and shows the afib began around 520 in the morning at a rate of 106 BPM. The afib was correctly diagnosed by the Kardia algorithm (Kardia only uses the term “possible atrial fibrillation” whereas Apple uses “atrial fibrillation” with the qualification that “this ECG shows signs of Afib.)

Later in the morning, the rhythm became a little faster (110 and 113 BPM) and a little more regular and the Kardia algorithm backed off from “possible atrial fibrillation” to “unclassified.” The regularity of the rhythm made it harder for Alivecor’s algorithm to be sure it wasn’t atrial flutter or SVT.

An Apple Watch recording she made a minute later continued to diagnose atrial fibrillation.

By 1034 AM she had converted to back to sinus rhythm at a rate of 49 BPM which Kardia correctly classified as bradycardia (sinus rhythm at rates 40-59 BPM will be classified as bradycardia by Kardia whereas Apple Watch will classify SR<50 BPM as “heart rate under 50. )

Apple Watch Versus Kardia

I primarily utilize Alivecor’s Kardia ECG device in conjunction with the KardiaPro online dashboard to manage my patients with paroxysmal (PAF) or persistent atrial fibrillation. As I’ve said before, this has eliminated the need for many outpatient long term monitors and has helped us manage the afib as an outpatient, thus avoiding ED , office and hospital visits.

However, a few of my patients have Apple Watch (Series 4 or later) and this also accomplishes the same goals. There is a significant difference in cost and functionality between the two devices

The Kardia single-lead device is .2 cm x 3.2 cm x 0.35 cm and weighs 18 grams. Recordings are made on a Bluetooth connected free smartphone app by putting your fingers on the left and right electrodes for 30 seconds. Current cost is $89.

Clearly it is not a wearable although it can be attached to your smartphone or its case and can be immediately available. It has no capability of detecting afib unless you make a recording.

Apple Watch on the other hand is clearly a wearable. Recordings are very easy to make by activating the ECG app and touching the crown with one finger for 30 seconds. These recordings then reside in the Apple Health app on your smartphone and can be shared by email with your doctor. The ECG function is available on Apple Watch Series 4, 5, and 6 but only Series 6 is currently being sold by Apple and the cheapest Series 6 is $399.

I asked my patient to summarize her thoughts on the relative value of the two devices for home monitoring and she told me

I like Kardia because your doctor can look at all the EKG records. I like Apple Watch because it warns me of an elevated heart rate when I am not doing physical activity.  I can then, just touch the crown and get an EKG reading.  All the information is right on my wrist.
The downside of the watch EKG,  Is the doctor does not have access unless I email a copy.

I think that summarizes the differences in a nutshell.

One key difference worth noting is that Apple Watch utilizes its PPG sensors to monitor your pulse periodically and generate alerts about abnormal heart rate or rhythms whereas Kardia can’t do that.

Another key difference is that Apple Watch ECG will not diagnose afib if HR<50 BPM or >120 BPM (see here) whereas AliveCor’s Kardia will confirm afib no matter what the heart rate (see here.)

Apple Watch Notifications: Irregular Rhythms, High Heart Rates and Low Heart Rates

Of note, the Apple Watch (AW) did not notify my patient that she had afib just that she had had a heart rate above 100 BPM for more than 10 minutes while at rest.

The high heart rate notification feature can be activated through the Apple Watch app on your iPhone. Go to Notifications then scroll down to “Heart.”

Options in Apple Watch Heart Health include “Irregular Rhythm” which notifies you if Apple thinks you have been in atrial fibrillation for >10 minutes.

However, my patient was alerted to a high heart rate (HR) which can be activated and set to go off at heart rates as low as 100 BPM or up to 150 BPM. A notification of high HR occurs when AW detects a high HR that rises above 100 BPM “while you appear to have been inactive for 10 minutes.”

(If your HR is normally below 90 BPM and at rest it jumps up to >100 BPM for more than 10 minutes there is a strong probability that an abnormal heart rhythm is occurring.)

The high heart rate alert can be set at values between 100 and 150 beats per minute. The low H

You also have the option of setting Apple Watch to notify you of low heart rate. This can be set to 40, 45 or 50 BPM and will alert if AW detects HR below the selected rate for 10 minutes. Slow heart rates in this range can be normal, especially if you run or do other endurance sports or if you are on a rate-slowing drug like a beta-blocker.

Personally, I have all 3 notifications on and have never received the high heart rate alert (set at 100 BPM) or the irregular heart rhythm notification. My low HR alert (set at 50 BPM) goes off pretty regularly right after I get up in the morning as my HR runs around 48 BPM then.

The Value of Home ECG Monitoring

This case highlights many of the ways that remote patient monitoring with personal patient ECG devices can improve patient care and facilitate innovative approaches to the enlightened medical management of afib.

First, these devices clearly reduce the need for patients to go to health care facilities and undergo expensive hospital-initiated monitoring.

Second, with the ability to know with certainty when a patient goes into afib and how long they spend in it we can be much more selective and individualized in the use of medications.

In some patients for example, we utilize a pill-in-pocket approach to the use of blood thinners, starting them as soon as the patient goes into atrial fibrillation.

In others, we utilize the pill-in-the-pocket flecainide approach wherein the antiarrhythmic is used to convert to sinus rhythm. In my patient’s case above, we gave additional flecainide to convert back to normal.

For many patients who suddenly go from normal rhythm to afib the heart rate jumps up and becomes tachycardic with rates up to and above 150 BPM. These patients typically feel symptoms mostly related to the high HR. An additional dose of a beta-blocker like metoprolol can slow them down and improve symptoms until the rhythm converts to normal.

Of course, any patient with afib should be managed in this way with the close advice, monitoring and counsel of their cardiologist.

If symptoms of chest pain, dizziness, or shortness of breath become more severe than the patient typically experiences with his/her afib episodes then a trip to the ED may well be in order.

Omnimonitoringly Yours,



10 thoughts on “Apple Watch Versus Kardia to Monitor Atrial Fibrillation From Home: A Case Study”

  1. Well done article. Very relevant to me. Also thanks for all the comments.

    I am a 78 year old runner and wear a Fitbit watch, which allows me to monitor and record my HR continuously. The watch (Versa 2) works perfectly at normal HR (50 – 120) and at night (40 – 50). During my High Intensity Interval Training, my HR goes up to about 150 for a minute or so at a time and dips to about 120 for about the same duration. The Versa 2 tracks that with reasonable accuracy. I have also tried wearing different watches during my HIIT with similar results (say 90% accuracy).

    That’s background. Here is the point: I recently noticed an unusually high HR during HIIT (~200), as identified by manual carotid pulse measurement, but noted that my Fitbit was showing ~120. The high HR usually occurred towards the end of my HIIT workouts and lasted from 3 – 30 minutes. So I captured an episode with my Kardia device. It was diagnosed as SVT by a Kardia doc. The Fitbit watch continued to show a HR of 120 during the SVT episodes which were running at a HR of 160-200.

    I then bought a Polar Pacer watch. It recorded the high HR episodes properly most of the time. I’m now considering having a loop recorder implanted to track possible SVT activity, which seems to occur only during extreme exertion. It does not yet occur during normal activities.

    Both the Polar record and the Kardia strip with a professional diagnosis were instrumental in the diagnosis and discussion with my cardiologist.

    Moral 1: A Fitbit watch can be very useful for normal wear, but the sensors get unreliable at a high HR, especially when it’s out of sinus rhythm, as during SVT. During those times, it seems the sensors can not be trusted. In fact, the HR readings are abnormally low. Polar and Apple watches seem to be more reliable when measuring non-sinus rhythms, even though I can not personally comment on the accurucy and reliability of Apple watches.

    Moral 2: My experience with the Kardia device has been excellent and I would trust it more than any watch.

    Question: Any thoughts about my SVT condition and “watch” and wait decision appreciated!

    • Gerry
      You’ve done quite a job of troubleshooting your arrhythmia utilizing kardia and Polar devices.
      I agree with Moral 1 and I’ve seen many patients with rapid Afib whose wrist-based wearable or watch tracked pulse as normal when they were going 150-160. not all of those electrical activations are transmitted at very high dosages due to reduced LV filling time.
      Glad to hear of your very positive experience with kardia.
      Not sure what your mean by “watch” and wait decision. Obviously the first part is monitoring with your devices. But what are you waiting for.
      For SVT (assuming that is what it is) low dose beta-blockers or diltiazem can be very effective at preventing episodes.I typically don’t recommend loop recorders for patients with SVT. Not sure how it would change the approach
      Dr. P

  2. Just an update to this. Apple has obviously updated the ECG software since this post was written. I just now got a confirmed atrial fibrillation at 150bpm on my Apple Watch.

  3. Dr P and I have corresponded on my Afib and I am sharing this as a FYI from a patient view of the Apple Watch, Kardia Mobile, and detecting Afib..

    First: The Question per Dr. P.: -how did AW alert you to the AFIB

    Background: I’m a 75 yr old male who had mitral valve repair surgery in 2008. Developed Afib after the surgery but corrected with Cardioversion in 2008. No problems since then and was not taking any meds for control of a recurrence of Afib. I was started on Atenolol in 2019 (25 mg/day) to correct lightheadness I was having.

    Back to the question: I was reading in my easy chair at night and wearing my Apple Watch. Sometimes, as I nod off in the chair, I would get an Apple Watch Low Heart Rate warning with the Watch dinging to alert me with a display saying “Your heart rate has been below 50 bpm for the last 10 minutes). I would get this because I was on 25mg Atenolol for about the last 1 year but was not on it before then. The last time I had Afib was in 2008 after Mitral Valve Repair.

    On the night of 7/10/20 the watch gave me the ding and the display said “Possible atrial fibrillation.”

    I then ran a watch EKG-showed the same message but I now also had an EKG chart. Chart said 90 bpm.

    I then ran several Kardia Mobile traces. All traces said possible AF. Sent one trace to Kardia for analysis-24 hrs later got back answer-confirmed AF.

    My action: on the night of 7/10/20 I called my family doctor, David Onstad, he called in an Eliquis prescription, which I started that night, and he had me increase Atenolol to 37.5 mg (was taking 25 mg). Onstad talked to his cardiologist colleague, Zachariah P. Zachariah, to discuss my case and what to do next.

    Saw Zachariah P. Zachariah, a few days later and he set up an in hospital procedure for a Cardiac Cathertization [plumbing check :)]. Did Cathertization on 7/22/20.
    Diagnose: Mild to moderate coronary atherosclerosis; Moderately severe impairment of the left ventricular function with a left ventricular ejection fraction between 40-45%; Status of post mitral valve repair without any significant mitral regurgitation. Recommended Cardioversion.

    Set up Cardioversion with the same EP who did it in 2008 (Jorge Flores). 200 Joules in 2008 with 1 jolt.
    Cardioversion done 8/21/20. 200 Joules, 1 jolt.
    From start of Afib (7/10/20) to NSR (8/21/20), 1-1/2 months.

    Status today, 10/10/2020. My Heart Rhythm Cardiologist (EP), Ahmed Osman, has implanted a loop monitor so we can collect some long term data. Next step still TBD. I’m now on 60 mg of Sotalol (20 mg 3xday) and working my way to lower dosage to reduce side effects. Osman says I can, my choice, go off Sotalol but I’m a little chicken of doing this so I’m working my way downward in dosage and will advise him if I’m comfortable with a dosage regime that minimizes side effect. 60 mg/da is a good candidate.

    Also I remain on 10 mg Eliquis (5 mg 2xday). I’m also on 40 mg generic Crestor (taking now a 20 mg 2xday) and Ezetimibe 10 mg taken 3 days a week.

    I am using a rowing machine 25 min a day, 5 days a week. HR starts at around 70 BPM and gets to 100 BPM in a very controlled manner. Row harder it goes up, less effort it goes down. HR recovery is 100 to 70 BPM in 2 minutes. A Apple Watch 6 EKG after rowing, durring recovery, shows Sinus Rthym. This all looks and feels good to me.

    My concern is what to do next, if anything?

    • Professsor,
      Thanks for sharing this. I have some clarification questions I’ll send you separately.
      Perhaps we could turn this into a separate post in follow up of my AW/Kardia comparison piece.
      A couple of observations.
      It’s unusual to be on both sotalol and a beta-blocker like atenolol as they both have beta-blocker properties. Typically, the dosage of sotalol is higher than what you are describing to be effective.The side effects of sotalol typically relate to its beta blocker properties.


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