Kardia's Fascinating SmartRhythm For Apple Watch Is Very Cool: Will It Allow Personal Atrial Fibrillation Detection?

The KardiaBand for Apple Watch from AliveCor has delivered on  its  unique promise of a medical grade single lead ECG recording made by placing your thumb on your wristwatch band.
The ECG recordings are equivalent in quality to those made by their previously available KardiaMobile (see my prior post here.) After more experience with the Band I think the ease of recording is superior to KardiaMobile and the ability to discriminate atrial fibrillation from normal sinus rhythm is similar to KardiaMobile.
By combining either a KardiaBand or a KardiaMobile device with Kardia’s SmartRhythm monitoring system for Apple Watch we now have the promise of personal monitoring to detect atrial fibrillation.

What is SmartRhythm?

SmartRhythm is AliveCor’s term for its system for monitoring your heart rate and activity levels in order to identify when your rhythm is abnormal.
The system “takes your heart rate and activity data gathered from the Apple Watch and evaluates it using a deep neural network to predict your heart rate pattern.”
The heart rate is obtained from the Apple Watch PPG sensor every 5 seconds.  If it differs from what is predicted SmartRhythm notifies you to record an ECG.
If you’d like to learn more detail about the development of SmartRhythm and how it functions, AliveCor has an excellent informational piece here.
You can choose to have the Kardia SmartRhythm display come up whenever your Apple Watch awakens. It’s got information on your heart rate and activity over the preceding several hours

SmartRhythm display. The light blue vertical bars representing heart rate range during an interval. The continuous lines above and below the vertical bars show the boundaries of heart rate predicted by the neural network based on your measured activity from the Watch accelerometer. . Upper left corner is yellow triangle indicating that the system detected potential abnormal rhythm and recommended a recording. The dot on the right is an ECG recording. The vertical bars at the very bottom represent steps taken during an interval

The AliveCor FAQ on SmartRhythm stresses that a notification does not always mean an abnormal rhythm. Clearly false positives can and will occur. The first day I wore my KardiaBand I had several of these.
Causes for false positives include exercise that Apple Watch couldn’t detect, stress or anxiety-in other words, situations where your heart rate is higher than predicted by how much activity you are doing.
The long term record of your SmartRhythm recordings resides on your iPhone . Here’s my record for the last week

Note that Kardia , in addition to tracking your heart rate, also shows you by the green, yellow and orange dots, the times that ECG recordings were made.
Green dots indicate recordings classified as normal and yellow as “unclassified.” In my case most of the unclassified recordings were due to heart rate >100 BPM associated with exercise.
There is one orange dot indicating that Kardia felt the ECG showed “possible atrial fibrillation.”
This happened when I took my Apple Watch off my wrist and put it on one of my patients who has permanent atrial fibrillation. I had him push on the KardiaBand sensor to make an ECG recording and it was correctly identified as atrial fibrillation.

Thus far I have had no notifications of “possible atrial fibrillation” while I have been wearing my watch thus the false positive rate appears acceptably low.

How Does SmartRhythm Perform During Exercise?

I checked out SmartRhythm’s ability to predict normal and abnormal  heart patterns by wearing it during a session on my indoor bike trainer. The device did a good job of tracking both my heart rate and activity during the workout.  You can view the most recent data by viewing your Apple Watch screen during the workout as below

Or for more detailed information you can view the complete history on your iPhone as below

The system accurately tracked my heart rate and activity (although AliveCor lists stationary bike as an activity that may result in false positives). During a session of weights after the aerobic workout despite erratic heart rates and arm movements it did not notify me of an abnormality. I also did 100 jumping jacks (which involves wildly flailing my arms) and the heart rate remained within the predicted boundaries.
What is more remarkable is that I was able while cycling at peak activity to make a  very good quality ECG recording by taking my right hand off the handle bar and pushing my thumb down on the KardiaBand sensor on my left wrist.

This recording clearly  displays p waves and is sinus tachycardia. It’s unclassified by Kardia because the rate is >100 BPM.

Afib Patient Experience

One of my patients last week, a 70 year old woman with paroxysmal atrial fibrillation, had already set up SmartRhythm monitoring on her Apple Watch.

The Apple Watch face of my patient with the Kardia icon bottom right. Note also that she has a Starbucks reward available

I have this patient like many of my afibbers utilizing KardiaMobile to check an ECG when  they think they are in afib.
However, she, like many of my afib patients, is totally unaware when her heart is out of rhythm. Such asymptomatic patients are alerted to the fact that they are in afib by detection of a rapid heart rate (from a heart rate tracking wearable or BP monitor) or an irregular heart beat (from BP monitor or by someone checking the pulse) or by a random recording of an ECG.
She’s started using SmartRhythm in the hopes that it will provide a reliable and early warning of when she goes into atrial fibrillation.
We discussed the possibility of stopping the flecainide she takes to maintain normal rhythm to test the accuracy of the SmartRhythm system for detecting atrial fibrillation in her but decided not to. She’s on an oral anticoagulant and therefore protected from stroke so development of atrial fibrillation will not be dangerous for her.
I eagerly await the first real world, real patient reports of SmartRhythm’s performance in atrial fibrillation detection.
If there are any afibbers out there who have had an episode of atrial fibrillation detected by  SmartRhythm please let me know the details.
We need such anecdotes along with controlled trials to determine how useful SmartRhythm will be as a personal wearable system for detection of afib.
Fastidiously Yours,
N.B. I’ve copied a nice section from AliveCor’s website which describes in detail the difference between measuring heart rate from the PPG sensor that all wearable devices use versus measuring the electrical activity of the heart with an ECG.

To understand how Kardia for Apple Watch works, let’s start by talking about your heart, how the Apple Watch and other wearable devices can measure your heart rate, and how an ECG is different from the information you get from a heart rate sensor alone.
Your heart is a pump. With each beat of your heart, blood is pumped through your arteries and causes them to expand. In the time between beats, your arteries relax again. On the underside of the Apple Watch is a sensor, called a photoplethysmogram (PPG), that uses green and infrared LEDs to shine light onto your skin, and detects the small changes in the amount of light reflected back as your arteries expand and relax with each beat of your heart. Using this sensor, the Apple Watch can tell how fast your heart is beating, and how your heart rate changes over time.
But, your heart rate does not tell everything there is to know about your heart. The PPG sensor on the Apple Watch can only see what happens after each heartbeat, as blood is pumped around your body. It can’t tell you anything about what is making your heart beat, or about what happens inside your heart during each beat. An ECG is very different, and tells you a lot more!

Three hearts showing a P-Wave, QRS-Complex, and a T-Wave

An ECG measures the electrical activity in your heart muscles. It detects the small pulse of electricity from the sinoatrial node (the body’s natural pacemaker, which normally initiates each heartbeat) and the large electrical impulses produced as the lower chambers of the heart (the ventricles) contract and relax. By looking at an ECG, a doctor can discern a wealth of information about the health and activity of your heart muscle, much more than you can tell from your heart rate alone. ECGs are the required gold standard for diagnosis of arrhythmias and many cardiac abnormalities, and can even be used to see evidence of acute heart attacks and even events that have occurred in the past.
Research has shown that taking frequent ECGs increases the likelihood of detecting certain arrhythmias, and decreases the mean time to diagnosis.


23 thoughts on “Kardia's Fascinating SmartRhythm For Apple Watch Is Very Cool: Will It Allow Personal Atrial Fibrillation Detection?”

  1. Smart Rhythm on the Apple Watch stops accurate exercise recording while it is running – values are reported in Activity but are totally inaccurate. This is acknowledged in Kardia documentation.
    So I wear Apple Watch 3 on right wrist with Smart Rhythm and Kardia band.
    And on left wrist Apple Watch 4 for Activity Monitoring- the Activity rings are also a great incentive to exercise. No comments or finger twirling as yet.
    Both Apple Watch 4 And Kardia band picked up irregularities later confirmed as PACs, which have resolved with some lifestyle changes.
    The PACS were associated with elevated BP, caused by high altitude skiing, and staying in ski village, with height up to 10,800 feet.
    The local cardiologist that I visited spoke of his experiences of visitors from sea level. Most showed significant elevation in BP, so meds had to be increased significantly to bring BP down. This is poorly documented.
    Both the new Qardio and the old Omron gave the wiggly heart icon, showing that both detected rhythm abnormalities- very impressive.
    The Autosleep and Heart Watch apps give interesting data with the AW4 – as Deming advised – what gets measured gets managed.

  2. It is my understanding that atrial fibrillation suppresses P waves but may not alter the overall average heart rate. This the typical case for me, and even your patient’s Watch screen shot shows a heart rate of 78 with a possible a-fib flag on the ECG. Did SmartRhythm issue an alert before the ECG, or was the ECG just taken because there was a known problem?
    Because SmartRhythm alerts depend on a heart rate occurring outside the predicted band for your activity level, it has been of little use detecting my paroxysmal a-fib. It would be of more use if it issued an alert upon detected beat-to-beat variability, which frequently does accompany a-fib episodes. From what I’ve read, this is not part of the analysis it does, but I could be wrong.
    The Kardia ECG apps do show that irregularity, as well as the suppressed P waves, and they flag it appropriately, but the magic is in getting the Watch to alert if you are asymptomatic. Now, I still have to rely on a “gut feel” and a pulse check to see whether it’s time to record an ECG. It would be great if AliveCor could enhance their SmartRhythm algorithms to include irregularity detection for issuing alerts.

    • Good observations. Perhaps with more data collection and deep learning Smart rhythm will be able to detect afib that is not associated with inappropriate tachycardia.
      Rather than afib “suppressing ” p waves, I would characterize the relationship as p waves representing organized atrial activity initiated usually by the sinus node and afib does not have any organized atrial activity.

  3. Hi Dr P,
    Thanks for your exercise max heart rate post, and your reply on this comments thread.
    RE: “my heart rate has a very defined peak at 140 BPM”
    In the watch screenshot when cycling, the 140-141 “cycling peak” is visible. Does the “Smart Rhythm Monitoring” allow expanding the running session heart rate readings to see if your HR gradually rose to 168, or suddenly jumped from a normal rising response curve?
    From Internet searches it seems, for non-tri-atheletes the “running peak” is +5% up to +20 bpm higher than their cycling peak. If a person is new to running, their running peak may be even farther from cycling peak.
    This is an interesting post and comments about this:

      • It has all the advantages and limitations of a single lead rhythm strip. I can interpret the vast majority of arrhythmias from a single lead rhythm strip including PVCs.
        It makes no attempt at this time to interpret or provide auto analysis for anything other than afib.

  4. I am curious as to if you observed sudden vertical line DRPS below the predicted algorithm? For example – I noticed that a long vertical line dropped from 75-80 bpm to the low of 50. I rarely get into the upper 50’s when I sleep and never to 50bpm, much less when I was supposedly awake and no symptoms. And then weird dots or blips that are at the 50bpm without it forming a line. No notifications or anything.
    It makes me wonder about the accuracy of the band. Would this be considered a false negative? According to the Kardia history – I have taken 110 ECG’s – all normal.
    Am I the only one who has observed this?
    Pictures Here: https://www.dropbox.com/s/l6t6fdw4lbt8eiq/20180305_123559.jpg?dl=0 and here: https://www.dropbox.com/s/ilyyy49whjngitd/20180306_200508.jpg?dl=0

    • With my Atriral Fibrillation (Persistent) with Rapid Ventricular Response, none of the wrist devices including the Apple Watch were ever as accurate at the wrist or at the elbow (BP Cuff), when compared to the heart rate strap that I wear 23 hours by seven days per week. As my Atrial Fibrillation has been gone for the last 10 days, they are much closer, but at times, in the past during non-NSR times, it could be off by as much as 30% at times.

    • The HR information comes from the Apple Watch PPG device. So the Kardia Band cannot be blamed for that.
      In some instances the PPG becomes inaccurate and yields faulty HR data.
      For example, often when I run the PPG displays HR of 180 BPM which I am incapable of achieving
      If is likely that the position of the watch or some motion artifact caused an inaccurate measurement of HR by the Watch.

    • I also see large downward HR spikes on my Apple Watch 3 going as low as 40 bpm. This spike downward is not detected by a polar H7 strap that is worn at the same time, suggesting that it is possibly an artifact. Alternatively it could be a pulse deficit? The downward spikes nearly always follow a brief movement then stoping/sitting down. My cardiologist assistant was not interested in the data and was totally dismissive of the reliability of the Apple Watch. I have an appointment with my cardiologist next week and will discus with her.

  5. I’ve been using Smart Rhythm on the watch now for the last couple of days. I’m impressed with the concept, but not necessarily impressed with the performance. As you know, I wear a Wahoo TICKR+ heart rate strap almost 24×7. I’ve always worn it, because I find that there are times when the Apple Watch will give me a lower reading than the chest strap. I assume that it has something to do with the rate of blood flow at the wrist not matching the detection at the heart but I don’t honestly know. I’ve had the problem with all wrist devices for the past year. My QuardioArm BP Cuff is slightly more acurate, but also suffers from the same inaccuracies. It could be that the Wahoo TICKR+ is picking up some of the Atrial Fluttering along with the normal Ventricle Fibrillation but I don’t honestly know.
    AliveCor has cool products, and I find them valuable in so many ways. But, Smart Rhythm annoys me because it keeps detecting out of range heart beats. These may actually be real, but since the pulse rate seems off; I just tend to view the information as false positives.
    All that said, you’d find the following podcast episode fascinating as it describes the machine learning used to develop their algorithms:
    You can also listen to the podcast.
    Another excellent article, but you already knew that…

  6. Looking over my Smart Rhythm history since I got the KardiaBand on 12-6, I noticed 3 heart rate spikes (over 160 bpm when I was not exercising). At the times they occurred I noticed nothing so did not take ECGs. The app manual suggests false spikes can occur right after putting on the band after charging my watch; it is quite possible that this is exactly what happened. Even when I’ve been exercising (mostly walking briskly), my HR has been below 120 bpm. Have you noticed this happening with your KardiaBand patients and yourself?

    • The Kardia Band is totally reliant for heart rate on the Apple Watch PPG system. At times this system gets fooled and registers a very high heart rate that is not correct. In particular I note the Watch likes to record a HR of 168 BPM when I’m running, a HR that I cannot achieve. Despite adjustments this usually persists.
      So, it’s not a Kardia Band issue per se, just a limitation on the data that the Kardia app is being sent

      • RE: “the Watch likes to record a HR of 168 BPM when I’m running, a HR that I cannot achieve.”
        Are you by any chance a “high beater”? I am, which really complicates discussions with my (marathoner) primary care physician. I am 65, with a resting HR of 55-59, and see 5k running HRave of 152-154 with interval HRmax of 178-179. Ten years ago, I did a Bruce Protocol to exhaustion and nausea at 10 MET with a running HRmax of 187 that rose briefly to 188 when I stopped. Twice I have verified my Polar chest strap is within 2-3 bpm of a three lead ECG at these high readings.
        I have been thinking about getting the Apple watch+AliveKor Kardia app+mobile device, but I don’t know if SmartRhythm was trained for “high beaters”. (Also I have to upgrade my iPhone5, so I am hesitating big time.)
        Your thoughts on “high beaters”?

        • I just wrote a post discussing the issue of higher than predicted maximal heart rates. check it out.
          But I realized that I never answered the question as to whether I was a “high beater.”
          I am virtually certain I am not because my heart rate has a very defined peak at 140 BPM or so. I’m on a beta-blocker which prevents it reaching the normal range of HR max for my age.
          I have not checked an ECG when the watch is registering 168 BPM but to be absolutely certain this isn’t an arrhythmia I would need to do that.

  7. I just got my KardiaBand and have only taken 2 ECGs. The first, with the free cardiologist evaluation, was normal, and my second , this morning, was reported normal on my watch. How often would you recommend that I take ECGs? I have asymptomatic afib but seem to have been in normal rhythm for almost 2 years. My last 2 week patch test, completed on 3-28, was normal. I had stopped taking flecainide on 1-22. I don’t want to waste my cardiologist’s time. How often, exactly what, etc. would you recommend I send to him? He wants me to send him abnormal results; is there a good reason to send him more than that?

    • For your circumstances I would recommend a daily ECG if you are not on an anticoagulant and weekly if you are. See my post on who should take anticoagulants.
      I would only send the cardiologist recordings that are identified as possible atrial fibrillation or unclassified if the heart rate is high.

  8. Unclear whether “SmartRhythm monitoring” has been FDA cleared too, as the Kardia Band systems’ INDICATIONS FOR USE don’t mention “HR monitoring” for activity mismatch:
    The Kardia Band System is intended to record, store and transfer single-channel electrocardiogram (ECG) rhythms. The Kardia Band System also displays ECG rhythms and detects the presence of atrial fibrillation and normal sinus rhythm (when prescribed or used under the care of a physician). The Kardia Band System is intended for use by
    healthcare professionals, adult patients with known or suspected heart conditions and health conscious individuals.


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