Tag Archives: Electrocardiogram

What Is The Cause of Low Voltage (Unreadable or Unclassified) AliveCor/Kardia Mobile ECG Recordings?

The skeptical cardiologist has had several of his readers submit stories and tracings of AliveCor Mobile ECG recordings which yield unclassified or unreadable recordings. In some cases this is due to excess noise but a lot of these tracings suffer from low voltage: the height of the tracing is very small.

John, a skepcard reader, is typical.

Recently, he noted his heart was racing and made an AliveCor recording which came back interpreted by the app as normal

First tracing. Note the QRS complex (the large regular spikes) are 2 boxes high. Right in front of them is a little bump, the p wave indicating normal sinus rhythm


Three hours later he made a second recording which has drastically lower voltage: the only deflections visible are tiny QRS complexes, the p waves have disappeared. I think this is also normal sinus rhythm but because p waves can’t be seen this came back uninterpretable and if there were any irregularity AliveCor would have called it atrial fibrillation:

Second tracing. Note the QRS spikes now are less than half of a box tall. There are no consistent p waves visible (unless one has a good imagination). The bumps after QRS spikes are T waves.

John has a theory on the cause of some of his low voltage recordings which I shall reveal in a subsequent post after testing it.

In the meantime, if any readers have suggestions as to causes of low voltage recordings or have noted similar issues please comment below or send recordings and observations to DRP@theskepticalcardiologist.com.

Voltagophilistically Yours,






AliveCor Smartphone App Detects Atrial fibrillation: Potential for Stroke Prevention

Atrial fibrillation (AF)  is a common abnormal rhythm of the heart which causes 1 in 4 strokes. Those afflicted with AF may lack any symptoms or only have a vague sense of irregularity of their heartbeat and thus the first symptom of AF can be stroke.

The gold standard for diagnosing AF has long been the electrocardiogram (ECG or EKG) and typically the ECG involves placing 12 electrodes on the chest/arm/legs and recording the electrical activity of the heart on an expensive device.

I’ve been checking out a device made by Alive Cor which works with your smart phone to record a single channel ECG and is capable of accurately diagnosing if you are in the normal (sinus) rhythm or in AF.
Screen Shot 2015-07-12 at 8.45.49 AMYou can purchase the third generation (significantly smaller then earlier versions) AliveCor Mobile ECG from Amazon or from AliveCor directly for 74.99$ and it works with an app with both iOS and Android devices.

I used mine with my iPhone 6. At first I carried it separately, fearing the added bulk when stuck on to my iPhone case but after a while I realized that it was never with me when I wanted to use it and that there was a huge risk of losing it and so I used the backing adhesive to attach it to my case.

After pairing the device with the app you put two fingers on each of the metal pads and the smartphone screen displays the recording. After 30 seconds of recording it then interprets the rhythm.

Screen Shot 2015-07-12 at 8.56.47 AM
Typical recording in normal sinus rhythm. The red arrow indicates the small p waves which are the electrical signal of the upper chambers (the atria) depolarizing , the blue arrow indicates the electrical depolarization of the ventricles (QRS). The orange arrow indicates that the time interval between the QRS complexes is the nearly the same for each beat, indicating the regularity that we expect when in NSR compared to AF.

Above is a typical recording I made in my office on a patient who had a history of AF. The quality is good and I can clearly see that he is in normal sinus rhythm. The app correctly made the diagnosis of NSR and calculated his heart rate at 68 beats per minute.

One day I had most of my patients record their ECG’s using AliveCor and compared it to the standard 12-lead ECG we normally record. The device correctly identified the two patients with AF out of this group and correctly identified the normals.

Screen Shot 2015-07-12 at 9.26.42 AM
AliveCor recording of patient with AF with heart rate of 70 beats per minute. Note the absence of p waves before the QRS complexes and note the beat to beat variation in the RR interval (orange arrow)

This recording is from a patient with persistent AF which had recurred two weeks earlier. The device correctly identified AF.

Studies have documented that AliveCor Mobile ECG can accurately diagnose AF in a screening setting and the FDA approved the device for AF screening in 2014.

Given the high prevalence of silent AF, the strong association of AF with stroke and the availability of anticoagulants which reduce AF associated stroke by 70%, screening for AF with devices like AliveCor holds the promise of preventing large numbers of stroke.

(For my comments on taking the pulse and stroke prevention see here and on the inadvisability of a routine 12-lead ECG see here)

AliveCor allows physicians utilizing the Mobile APP and ECG to have a “dashboard” into which their patients can transmit their AliveCor ECG recordings.

I will be discussing this remarkable new device with my AF patients  who are smartphone enabled. I think it will advance our ability to more efficiently and quickly diagnose AF in them.

My standard approach if a patient with AF calls and says that they feel like they are out of rhythm is to have them come into the office for a full 12-lead ECG. If they are AliveCor enabled, they could make their own recording, and we could review that remotely and make a diagnosis without the office visit.

Let me know your thoughts on smartphone ECGs.

fibrillatorily yours,


Should You Get a Routine Annual Electrocardiogram (ECG)?

Recently, the skeptical cardiologist  was asked by his  old friend and life coach (OFALCSC) whether he was correct to refuse the annual electrocardiogram (ECG) which his primary care doctor had recommended during an annual physical.

ECG showing atrial fibrillation
ECG showing atrial fibrillation

Most of my patients feel that the ECG has the ability to tell me  quite a bit about their heart. The technique utilizes electrodes on the arms, legs and chest region which  record with precision, the depolarization and repolarization of the upper chambers (atria) and lower chamber (ventricles) of the heart.

The ECG is THE tool for assessing the rhythm of the heart.  If performed and interpreted properly (not always a given) it tells us very precisely whether we are in normal (sinus) rhythm, wherein the atria contract synchronously before the ventricles contract, or in an abnormal rhythm. It is also very good at telling us whether you are having a heart attack.

If you are, however, like the OFALSC, and feel fine (meaning without symptoms or asymptomatic), exercise regularly, have never had heart problems,  and have a pulse between 60 and 90, the value of the routine annual ECG is very questionable. In fact, the United States Preventive Services Task Force (USPFTF)

“recommends against screening with resting or exercise electrocardiography (ECG) for the prediction of coronary heart disease (CHD) events in asymptomatic adults at low risk for CHD events”

(for asymptomatic adults at intermediate or high risk for CHD they deem the evidence insufficient). The USPSTF feels that that the evidence only supports an annual BP screen along with measurement of weight and a PAP smear.

To many, this seems counter-intuitive: how can a totally benign test that has the potential to detect early heart disease or abnormal rhythms not be beneficial?

There is a growing movement calling for restraint and careful analysis of the value of all testing that is done in medicine. Screening tests, in particular are coming under scrutiny.
Even the annual mammogram, considered by most to be an essential tool in the fight against breast cancer, is now being questioned.

My former cardiology partner, Dr. John Mandrola, who writes the excellent blog at http://www.drjohnm.org, has started an excellent discussion of a recent paper that shows no reduction of mortality with the annual mammogram. He looks at the topic in the context of patient/doctor perception that “doing something” is always better than doing nothing, and the problem of “over-testing.”

In my field of cardiology there is much testing done. It ranges from the (seemingly) benign and (relatively) inexpensive electrocardiogram to the invasive and potentially deadly cardiac catheterization. For the most part, if patients don’t have to pay too much, they won’t question the indication for the tests we cardiologists order. After all, they want to do as much as possible to prevent themselves  from dropping dead from a heart attack and they reason that the more testing that is done, the better, in that regard.

The Problem of False Positives and False Negatives

But all testing has the potential for negative consequences because of the problem of false positives and negatives. To give just one example: ECGs in people with totally normal hearts are regularly interpreted as showing a prior heart attack. This is a false positive. The test is positive (abnormal) but the person does not have the disease. At this point, more testing is likely to be ordered; specifically, a stress test. Stress tests in low risk, asymptomatic individuals often result in false positive results. After a false positive stress test, it is highly likely that a catheterization will be ordered. This test carries potential risks of kidney failure, heart attack, stroke and death. It is bad enough that the cascade of testing initiated by an abnormal, false positive,  screening test results in unnecessary radiation, expense and bother but  in some cases it end up killing patients rather than saving lives.

On the other end of the spectrum is the false negative ECG. Most of my patients believe that if their ECG is normal then their heart is OK. Unfortunately the ECG is very insensitive to cardiac problems that are not related to the rhythm of the heart or an acute heart attack.

Patients who have 90% blockage of all 3 of their major coronary arteries and are at high risk for heart attack often have a totally normal ECG. This is a false negative. The patient has the disease (coronary artery disease), but the test is normal. In this situation the patient may be falsely reassured that everything is fine with their heart. The next day when they start experiencing chest pain from an acute heart attack, they may dismiss it as heart burn instead of going to the ER.

More and more, screening tests like the ECG and the mammogram  are rightfully being questioned by patients and payers. For a more extensive discussion about which tests in medicine are appropriate check out the American Board of Internal Medicine’s http://www.choosingwisely.org.

Keep in mind: not uncommonly,  doing more testing can result in worse outcomes than doing less.