AliveCor Mobile ECG : Ways To Minimize Low Voltage and Unclassified Recordings

(This post was updated 4/13/2023)

Sometimes AliveCor’s Mobile ECG device yields unclassified interpretations of recordings.

Understandably if you want to know whether your rhythm is normal or atrial fibrillation, the unclassified  classification can be very frustrating.

There are various caues of an unclassified tracing with different solutions. In the past, some unclassified recordings were due to a heart rate over 100 BPM or under 50 BPM and could not be fixed. Kardia now (2023) will describe these as tachycardia and bradycardia respectively.

When I first wrote this article in 2016 I noted that “patients with ectopic beats like PVCS may consistently generate unclassified interpretations (see my discussion here).” Kardia is now capable of identifying PVCs and premature atrial contractions if one subscribes to their Advanced Determinations.

Noise or Artifact Related to Poor Technique

Artifacts induced by poor recording techniques are common as a cause and almost always can be fixed.

These can be reduced by minimizing motion, extraneous noise, and maximizing contact with the electrodes.  Follow all the steps AliveCor lists here.
For me, the following step is crucial

  • If your fingers are dry, try moistening them with antibacterial wipes or a bit of lotion


Low Voltage As Cause of Unclassified Kardia Recordings

Another cause of unclassified interpretations is a low voltage recording (which I initially discussed here.).

Low voltage recordings are often due to a vertically oriented heart. Recording using the lead II technique can often solve the problem.
Lead II involves putting one electrode on your left knee and one your right fingers as described in this video:

Reader “J”  recently sent me a series of Kardia ECG recordings,  some of which were unclassified, some normal and one read as possible atrial fibrillation.
The unclassified and possible AF tracings looked like this:
They were very regular with a rate between 80 and 100 BPM but they totally lacked p waves. It was not clear to me what the rhythm was from these tracings.
Other tracings had lowish voltage but the p waves were  clearly visible  and Kardia easily classified them as normal

Lowish voltage with p waves (Type B)
Good QRS voltage with clear p waves ( Type C)

Still others had improved QRS voltage with clear p waves and were also classified  appropriately as normal

After some back and forth emails we discovered that the ECG recordings with no p waves were always  made using the chest lead recording.   AliveCor-describes this as follows:

  • For an Anterior Precordial Lead, the device can be placed on the lower left side of the chest, just below the pectoral muscle. The bottom of the smartphone or tablet should be pointing towards the center of the body.

Mystery solved!
There is an abnormal cardiac rhythm that is regular between 80 and 100 BPM with no p waves and normal QRS called junctional tachycardia but in J’s case the absent p waves are related to the recording site.
Also, note that for this young woman the lead II voltage (Type B tracing) is much higher than the standard, lead I voltage (type A tracing).

Lead II With Pants On

After Dr. Albert told me of the advantages of Lead II I responded that it seemed somewhat awkward to take one’s pants off in order to make an ECG recording.
He immediately reached in his suit pocket and pulled out a pen-shaped device and began spraying a liquid on his left knee.
To my surprise he was able to make a perfect Lead II recording without taking his pants off!
Lessons learned from reader J and Dr. A:

  • Consider trying different leads if the standard Lead I (left hand, right hand) is consistently yielding unclassified ECG recordings
  • Try Lead II (left knee, right hand) to improve voltage and recording quality
  • You can record off your knee even with your pants on if you are prepared to spray liquids on your pants

Pantsonically Yours,


14 thoughts on “AliveCor Mobile ECG : Ways To Minimize Low Voltage and Unclassified Recordings”

  1. I just purchased a single lead Kardia. At first I couldn’t get any reading but I am able to get normal sinus rhythm now however the peaks on the EKG are so small! When I try my knee or the lower left chest it works so much better. Is there any time of issue with having low lead 1 voltage? If there was an issue it would show up on a regular 12 lead EKG from my doctor, correct? You can see all the voltage on all the leads on a 12 lead EKG?

    • Sarah,
      There are no known problems with having a low voltage in lead I. 12 lead ECGs will show voltage in all 12 leads.
      Dr p

  2. I’m having the same issue on with my apple watch ECG. A lot of times very low QRS amplitude and classified as inconclusive. I found turn my left arm a little backward or turn my body left (watch is on my left wrist) increases the amplitude a lot! I’m not sure if I need to worry about it or not. Plus apple watch sometimes show very low heart rate like ’43’ but when my resting hr is ususally 60-70.

  3. I have cardiac sarc with normal ekgs and holters. So no ICD. Palpitations more frequent so I wore a ZIO patch for two weeks. It picked up a 5 beat SVT, 3 beat ventricular trigeminy as well as shorter runs of SVT, PACs. Had a lot of unclassified Alive cor readings always come back when reread as normal. Had a bunch of ‘a fib’ readings which EP called artifact. Cardiac sarc unchanged on PET despite a year of methotrexate, 6 months of Remicade. On IVIG for progressing neurosarc and now PET shows thoracic lymph node involvement. Sarc raging in the rest of me-arthritis, neuro, liver. Yet cardiologists act hopeful they can reverse the cardiac part with no mention of seeing EP doc or future ICD due to new conservative protocols. Just wondering if you are as skeptical as I am!

  4. Dr.
    Have you seen this?
    This is a 20 dollar board that, with minimal electronics knowledge, allows one to assemble an EKG. If you scroll down you can see that the waveforms produced are quite stable.
    I’m in the process of assembling one. Obviously, AliveCor is FDA approved, etc, but fundamentally it’s the same or very similar hardware as to what’s going into this single lead EKG.

  5. Im wondering if you have caught an ekg on the Kardia band of a rate greater than 200 and have what that might look like.
    I don’t think the Kardia band can keep up with such a rate. What is your experience with it at a rate this high? Mine look like artifact but I know it isn’t as I have had previous episodes of VTach. Also was symptomatic and that was the reasoning for taking an ekg. The smart rhythm also alerted me to take a reading as well. Thanks.

  6. Very interesting report on unclassified Alivecor readings. So far I have not experienced these kinds of readings but I will use the techniques described if I ever have a problem.


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