The Skeptical Cardiologist

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 Sure enough, the nice green dots showing sinus rhythm had been replaced by the orange dots of atrial fibrillation (afib.)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,


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