A Comparison of Alivecor’s Kardia 6L and Kardia Single Lead Mobile ECG With and Without the V2 Algorithm

The skeptical cardiologist has long been an advocate of the Kardia single lead mobile ECG for personal monitoring of cardiac rhythm. In conjunction with the KardiaPro dashboard, it drastically reduces the need for expensive long-term monitoring and has reduced the need for ED visits and hospitalizations for many of my patients.

Although I welcomed the Alivecor’s six-lead version of Kardia and found it to be a marvel of modern engineering, I had heretofore not found compelling reasons to recommend it to my patients over the less expensive single lead.

A reader, John Lorscheider, who has used the single-lead Kardia for 5 years to monitor his atrial fibrillation has provided me with his excellent detailed comparison of the 6L to the single lead. In addition, he has upgraded to the V2 algorithm (which I discuss here) and provides some excellent comparative information on the performance of both the single lead and six lead devices with this upgrade versus V1.

Of note, John writes “The V2 upgrade and other extra features are only available with the KardiaCare Membership.” Most of my patients are already paying $99/year for the premium service which allows storage of their ECGs in the cloud and allows me to view all ECGS and Omron BPs on my KardiaPro dashboard and I assume they will have or will be transitioned to the KardiaCare Benefits. (Alivecor please confirm.) What follows is John’s personal rhythm history followed by his analysis.

First a bit of background. I was initially diagnosed 5 years ago with AFIB.  I was entirely asymptomatic at that time and the AFIB was coincidentally picked up in a routine physical by my internist.  After a complete workup, I was labeled with paroxysmal AFIB and hyperthyroidism. Once the thyroid issue was corrected, I returned to sinus rhythm, at least for a while.  I’ve used the Kardia single-lead device for 5 years now to spot check for AFIB.  My paroxysmal AFIB has only been detected in a clinical setting once over 5 years.  With the Kardia device, I detected AFIB dozens of times in my home.  I can just print out the EKG and hand it, email it or upload it to my cardiologist’s EMR patient portal, MyChart, if I need to.  Faced with the prospect of untreated and potentially advancing AFIB to persistent or permanent status, the purchase of the Kardia unit was a no-brainer.
In the past year, I began experiencing frequent tachycardia spikes (180-200 BPM) when I was cycling at a normal 130-140 BPM zone while endurance cycling according to my Polar H10 heart rate sensor and Polar Beat iPhone App.  I also made an appointment with my cardiologist who did a complete workup and everything checked out fine,  He fitted me with a 5-day event monitor and the abnormal results while cycling correlated nicely with my heart rate monitor’s activity.  He attributed the tachycardia to exercise-induced adrenaline surge. 
However, the echo showed that I also developed a severely enlarged left atrium which I didn’t have 5 years ago.  That dilation was likely due in part to the high intensity and long duration of frequent endurance cycling and running which I have done for may decades, and perhaps the AFIB as well.  The AFIB has returned and is now very symptomatic.  The single lead Kardia works very well for AFIB determination but it has some drawbacks.  I’ve been on Metropolol (daily), Flecainide (pill-in-a pocket) and Eliquis which works well, along with a reduced training load and a few lifestyle tweaks.  Perhaps my endurance exercise finally caught up with me at age 67. 
I recently purchased the Kardia 6L device to compare with the Kardia single-lead device and upgraded to the Kardia app with the V2 algorithm.  These are my comparisons between the two:
Kardia Single Lead Device with Version 1 Algorithm:

  1. Highly accurate for diagnosing: 
    • AFIB 
    • Bradycardia
    • Tachycardia detection to 300 BPM (Originally was only to 100 BPM)
    • Indicates current heart rate
  2. You can email yourself an EKG and print it out or email it to your cardiologist
  3. Stores your EKG’s on your SmartPhone (uses almost no smartphone memory)
  4. Device runs a onetime $89
  5. SmartPhone App is free of charge


  1. Very prone to electrical interference from appliances, TV’s, radios, computers, etc. making the Kardia recording “Unreadable”.  It’s sometimes hard to find a “quiet” place without interference.
  2. The single lead device needs to access the microphone on smartphones and cannot be used when a person is wearing BlueTooth enabled hearing aids.  The hearing aids must first be turned off in order to do a recording.
  3. The single lead device must be positioned with 1-2” of the phone’s microphone to make a recording.  Any further away it will not connect with the phone.
  4. This is a desktop device and not wearable so it can’t be used during exercise.

Kardia Single Lead Device with Version 2 Algorithm:

  1. Same Pros as above plus:
  2. The V2 upgrade performs all of the V1 functions above along with the following “Advanced Determinations” that previously were labeled as “Unclassified”
    • Sinus Rhythm with Premature Ventricular Contractions (PVCs).  I get a few of these and they seem quite benign.
    • Sinus Rhythm with Supraventricular Ectopy (SVE)
    • Sinus Rhythm with Wide QRS
  3. Stores the EKG’s in AliveCor’s cloud
  4. The V2 upgrade and other extra features are only available with the KardiaCare Membership https://store.alivecor.com/products/kardiacare


  1. Same cons as above plus:
  2. The V2 algorithm upgrade with the “Advanced Determinations” is not free and costs $99 per year for an annual membership.  It’s worth it for me, but maybe not everybody.  $99 wouldn’t buy me a seat in my cardiologists waiting room, much less an office follow-up visit to see him.
  3. You get a host of added features with a membership, but some are useful and some are not.  https://store.alivecor.com/products/kardiacare

Kardia 6L Six Lead Device with Version 2 Algorithm Pros:

  1. Same Pros as above plus:
  2. The 6L communicates with smartphones via BlueTooth with a simple discrete device pairing.  It does not communicate by sound with the smartphone’s microphone like the single lead Kardia unit does.  This allows for a greater distance capability between the 6L and the SmartPhone. 
  3. The 6L appears less prone to electrical interference 
  4. The 6L device has an advantage over the single lead device in that BlueTooth hearing aid wearers don’t have to turn off the hearing aids prior to taking a reading.  I suspect many Kardia users may wear hearing aids too.
  5. AliveCor’s website states: “FDA-cleared and doctor recommended: The most clinically validated 6-lead personal EKG, FDA-cleared to detect AFib, Bradycardia, and Tachycardia.”  Wait a minute, that’s what the single lead Kardia device does!  Color me skeptical. 


  1. AliveCor doesn’t appear to provide a clear explanation of what the 6-lead diagnostic advantages are for either the doctor or the patient.  Two cardiologists I spoke with don’t see the advantage of the 6-lead device over the single lead device either.  This makes me even more skeptical.  Perhaps you or one of your followers could enlighten me.
  2. The 6L is costlier at $149 and for V2 algorithm requires a $99 annual membership.  OK, I’ll pay it just because of the greater range, less interference, and being able to keep my BlueTooth hearing aids on when I take a recording.

John Lorscheider lives in Southeast Wisconsin and he and his wife and are now retired. He was in sales, engineering and and senior management for industrial pumps and fluid process equipment for various manufacturers for 40 years. 
He has also written for and moderated several web medical forums in his spare time.  His leisure time is spent between cycling, running, traveling, cooking, enjoying family and friends, listening to music, along with reading and finding the many biases and flaws in medical trials.

Skeptically Yours,



14 thoughts on “A Comparison of Alivecor’s Kardia 6L and Kardia Single Lead Mobile ECG With and Without the V2 Algorithm”

  1. To make the 1 lead KardiaMobile wearable: place disposable electrode (3M, Red Dot) over each pad as well as over right chest just below midclavicle and left chest at V4 position. Connect the pads to chest electrodes with leads having alligator clips at each end. Run app as usual.

  2. Dr. Pearson,
    Any new thoughts on the 6L? I’m ordering one… my wife’s experiencing signs of long-COVID with sympathetic and parasympathetic manifestations. She’s also got a history of occasional ventricular ectopy when volume depleted… I’m concerned after a presyncopal episode that I need another tool in the bag.

    • Gerry,
      I generally advise getting the 1L for rhythm issues if you are relying on the algorithm
      It is simpler to use, cheaper, and both devices utilizes Lead 1 for diagnosis.
      Dr P

  3. I first heard about Kardia/AliceCor in 2017, after my husband hand a true MI. I have comfort in that if not feeling well, I can use this product with confidence and make an intelligent decision about 911 or ER trips. It had picked up A-fib as many times as I have use it for my husband. The implantable loop monitor did pick it up and stopped working over a 1 year ago. According to the manufacturer the battery has a 3-year life expectancy. The cost of this product does measure up to their claims. I have confidence that both of us can make intelligent decisions about heart care.

  4. I have been a very satisfied user for many years of the original Kardia one lead (two fingers), and have occasionally send off ECGs for expert analysis. PVCs were picked up skiing at very high altitude, quite a common situation according to the local cardiologist.

    How can I check whether my Kardia has the latest software update? Your advice and comments appreciated.

    Cutting out alcohol certainly helps reduce the incidence of PVCs, and may help in the eternal battle of the bulge.

    BTW I have found the Kardia a great reassurance after 6 days in the ICU. I had my Astra Zeneca COVID vaccination 5 weeks ago, which prompted severe migraines for a week. 9 days later I went to the ED, advising them I likely had blood clots after my COVID jab. Massive clot in one leg stretching from ankle to groin, with a number of clots in my chest, affecting my heart. Now home on blood thinners and crutches, and very reassured heart is good according to Kardia.

    A rapidly dropping pulse oximeter reading while I was in the ED waiting room was an indication that clots were taking place at that time, and getting worse by the hour.

    Please note that the Apple Watch 6 may erroneously report a normal Oxygen percentage if the patient is anemic, while a hospital grade pulse oximeter will compensate for the anemia, and report the correct lower value. I am planning to upgrade from AW4 to AW6 for this pulse ox feature – my frequent blood tests should mean undetected anemia is highly unlikely, and the AW6 may help monitor my lung and heart function.

    Comments on AW6 and Oxygen measurement are welcome, plus any experience with hospital grade pulse oximeters and home use.

    • Hi Mr. Blair,

      Was reading this blog looking for info regarding the EMAY and read your compelling story. I’m wondering if your experience with the Vaccine was reported to VAERS? I’m glad you are doing well. Good luck to you!

  5. I am “ grandfathered in “ as Kardia calls it because I have been a customer from the very beginning . I have had afib one time that was actually able to be recorded . I suffer and I do mean suffer from pvcs to the point of bigeminy and trigeminy. Kardia is a life saver for me . If I have any questions about my readings I simply send them to my cardiologist:)

  6. I’ve used the single lead Kardia Mobile since 2015, and it has been 100% accurate in confirming when my chest fluttering and racing pulse = AFib. Since that time, I’ve been on variable medical regimens, currently Atenolol Beta Blocker, Atorovastatin, Benazepril, Pradaxa, and recently sublingual Nitro & Isosorbide Mononitrate. After 6 cardioversions, last year’s Ablation seems to have halted AFib, but a recent ZIO Patch test showed 16 Supraventricular Tachycardia runs (my Doc says ‘no worries’ with these).

    In December I upgraded to the Kardia 6L, and think it’s a great improvement. My daily BP readings using my Omron BP device echo easily to my the Kardia iPhone/iPad software, along with history of my 6L EKGs. My portable devices have a full & current history of ‘official’ and Kardia / Omron readings wherever I am.

    The 6 Lead gives me very credible Limb Lead results: Leads I, II, III, aVR, aVL, and aVF (but not the precordial leads V1-V6). This basically gives me useful EKG information about the right sided and posterior aspects of my heart.

    Specifically, my Kardia 6L gives me an EKG picture of the Inferior Wall of my heart fed by my Right Coronary Artery (Leads II, III, and aVF) as well as the Lateral wall of my heart, fed by my Circumflex Artery (Leads I and aVL). I’m NOT getting a view of the Septal or Anterior walls of the heart (V1-V4).

    Therefore the 6L can alert me to the possibility of some (not all) heart attacks, including inferior, true posterior, and right ventricular Myocardial Infarctions. I can watch for ST elevations or depressions and Pathologic Q waves in leads II, III, aVF. (See, for example: https://ecg.utah.edu/lesson/9 and the excellent Life in the Fast Lane medical site: https://litfl.com/).

    Further, in addition to the Brady/Tachycardia pulse rates & PVCs both devices show, my reading suggests the 6L when properly read can alert me to dangerous ventricular tachycardias included the deadly Torsade De Pointes, and AV blocks (2nd degree, Mobitz II, 3rd degree), left anterior fascicular blocks (rS complex in Leads II, III, aVF with small R and deep S waves), axis deviations, Pathological Q waves, wide QT intervals placing me at risk for ventricular arrythmias, hyperactute T waves preceding a ST elevation MI, newly developed inverted T waves that can suggest several pathologies, and certainly more. I’m still learning, and all of us could use some professional guidance.

    To date, I have not suffered a heart attack, but I now experience daily angina. A recent CT-Angiogram shows one of my coronary arteries is 50% occluded. I have seen what I identify as ‘fragmented’ QRS complex (fQRS) in my Kardia’s 6L in Leads III and aVF, and an inverted T Wave in III. I’m worried that my heart’s ‘electrical’ problems may now include ‘plumbing’ (ischemia) problems.

    I’ve read that:
    “The presence of fQRS in lateral leads (I, aVL, and V6) predicts
    myocardial scar in the lateral myocardial segment or left
    circumflex territory myocardial scar. The presence of fQRS
    in inferior leads (II, III, and aVF) predicts myocardial scar in the
    inferior myocardial segment or in the right coronary artery territory. ”
    (see: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3443879/ and also https://pubmed.ncbi.nlm.nih.gov/20129288/)

    I have sent Kardia 6L reports to my cardiologist, who refers to the device as a ‘toy’ and has consistently discourage my use of it. That said, I will continue to listen to my cardiologists’ medical advice while using my 6L whenever I feel particularly “bad” to get a clue whether I should visit the ER or call the Cardio’s office. The device, and my own wide reading, allow me to do an initial but critical triage of my own symptoms without entangling professional help unnecessarily.

    I do recommend the Kardia 6L, and hope cardiologists like Dr. Pearson will comment on the emerging value of the device in these expanded ways.

    • Frank:

      That’s a great analysis of the potential “off-label” benefits of the 6L vs. the single lead Kardia device. I suspect AliveCor wouldn’t endorse that as they may get their wrist slapped by the FDA if they were to overstate what their devices were approved for in the first place.

      Question: You state the 6L can detect 2nd degree AV block if the EKG is read properly. Just how does the 6L quantify that PR interval conduction prolongation?

      • As I understand it – 2nd degree AV Block occurs because the AV node is dysfunctional, causing a gradual prolongation of the PR interval over a few cycles – leading to pauses when the P wave is blocked and the QRS spike is skipped. In Mobitz type 1 the interval leads to a repeatable pause pattern (Wenckebach), and in Mobitz type II the QRS pauses are more sporadic – a less consistent pattern.

        The 6L PDF report effectively simulates a paper EKG. Each ‘small box’ = 1 mm or 0.04 seconds. The typical PR interval duration: 0.12- 0.2s or 3-5 small boxes (variable by exercise and other pulse rate changes). See:

        With the 6L we can zoom in on the PDF to easily see the PR intervals (typically on Lead II) count the number of ‘little boxes’ or portions thereof, leading up to a paused QRS complex. The 6L doesn’t do the counting for us … we need to simply count the ‘little boxes’ or parts of boxes.

        Here are some EKG examples showing this:
        A) 2nd Degree AV Block: Mobitz type 1 (Wenckebach) & Mobitz type 2 block

        B) The Life in the Fast Lane medical blog (this one on 2nd degree AV Block):
        shows several EKG examples

        Finally – while it is true the FDA has approved the Kardia’s offering ‘Advanced Determinations’ (aka pre-packaged opinions) for

        Atrial Fibrillation
        Normal Sinus Rhythm
        Sinus Rhythm with Premature Ventricular Contractions (PVCs)
        Sinus Rhythm with Supraventricular Ectopy (SVE)
        Sinus Rhythm with Wide QRS
        this only limits what the Kardia can offer as a pre-packaged printable opinions on what the EKG (probably) shows. It does not limit how a medical professional (or informed patient) can spot EKG patterns suggestive of, or demonstrative of, a much wider range of cardiac arrhythmias or possible ischemic events visible on the 6L.

        Thanks again to Dr. P (and to you & all who post here) for helping bring us up to speed!

        • Frank,
          That’s a pretty accurate summary. A cardiologist can read all manner of rhythms and heart blocks from a good quality Kardia single lead or 6 lead recording. I would describe the second degree AV blocks differently
          With Mobitz type I, second degree AV block there is a progressive prolongation of the pr interval until the a complete failure of the electrical signal transmission from atria to ventricles occurs resulting in a dropped QRS or ventricular beat.
          With Mobitz type II, there is fixed pr interval but every second, third or greater beat is totally blocked


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