Were your 12-lead ECG electrodes placed where they should be?

by Carolyn Thomas    ♥   @HeartSisters

If you’ve had as many 12-lead ECG tests as I’ve had done over the years since my heart attack, you too may marvel at how swiftly the nurse or paramedic or Stress Test Clinic tech can slap those sticky electrode patches onto your chest, arms and legs.  Having observed many people slapping patches on me, I often wonder:  how do they know if they’re attaching those electrocardiogram patches onto the right anatomical places?       .  

An electrocardiogram measures electrical activity of the heart. ECG and EKG are abbreviations for the same test (EKG comes from the original German, “elektrokardiogramm“). Basically, there are three steps in performing this test:

1. preparing the patient and their skin
2.  accurate electrode placement (12 leads, calculated using 10 electrodes attached to small, sticky patches: six placed on the chest, one on each leg and arm)
3. checking the electrocardiograph settings and other equipment required

It turns out, sadly, that not everybody excels in Step #2. 

Studies suggest that mis-positioning of ECG electrodes may affect up to four per cent of patients. That statistic might seem puny – until you remember that, in the U.S. for example, it covers several hundred thousand out of the 40 million ECGs recorded every year. The disturbing conclusion of researchers: “The most common technical factors for surface electrode mis-positioning are carelessness or haste.”(1)

It’s easy to imagine then, a crowded Emergency Department on a crazy-busy night. It can be distracting even for skilled staffers trying to carefully apply ECG electrodes to precisely correct body points. I’m guessing that a less experienced healthcare professional could be even more distracted. 

Two bits of ECG TRIVIA: 

• in a review of Google Images of human torsos with ECG leads, the only images available were of white men  (Yep, see image below*) and worse, the majority showed incorrect lead placement.(2)
• inaccurately placed ECG electrodes are apparently most often seen in hospital Intensive Care Units.

Studies on this issue typically view the biggest problem as false positive results (a misplaced electrode will NOT provide normal-looking results, so may be misinterpreted as something wrong with this particular heart – not with the skills of the person placing the ECG leads). So some of these patients, despite no coronary heart disease, will have false positive test results. This can be an expensive mistake resulting in further cardiac tests and procedures. Consider that the national gross charge in the U.S. for a cardiac stress test can range from $1,200 to $11,700.(3)   Some patients have even been referred to the cardiac cath lab  for more expensive and more invasive (and unnecessary) angiography procedures – based on false positives.

Here’s an example of how even one mis-positioned ECG lead can distort your test result, from Dr. Stephen Smith, an Emergency physician who teaches Emergency Medicine at the University of Minnesota, but more importantly, he and his team teach others all about ECGs.  He identified improper placement of one electrode after he noticed a pulse tapping artifact (interference) in this ECG of a 60-year old man with chest pain who came to his Emergency Department.

“This is when an ECG electrode (in this case, in the left leg lead) is placed near an artery and is affected either by the mechanical action of the artery, or possibly by the electrical conduction of the blood in the artery.” 

After Dr. Smith asked his tech to move that electrode slightly, the artifact disappeared.

But consider this:  even with appropriately placed ECG electrodes,  it can be challenging for many physicians to correctly interpret the results of your ECG (unless Dr. Smith works in your hospital).  The accuracy of physician interpretation of ECGs can be surprisingly low.(4)  

Dr. David Cook, lead author of a 2020 study on physician accuracy in interpreting ECGs, concluded in his team’s review of 78 published studies that on average, only half of all ECGs are accurately interpreted, with medical students having the lowest accuracy and – not surprisingly – cardiologists having the highest accuracy at 75 per cent.  When Yale cardiologist Dr. Harlan Krumholz reviewed this report for the New England Journal of Medicine’s Journal Watch, he wrote: 

“This sobering study reports low accuracy in the interpretation of electrocardiograms across a wide range of groups. Cardiologists did best, but still had a high prevalence of errors. And training had only a modest effect in the studies.”

That’s sobering indeed, especially if you’re a heart patient like me whose heart attack was misdiagnosed as acid reflux after my ECG was interpreted by an Emergency Department physician as “normal”.  That was right before he sent me home, feeling horribly embarrassed because I’d just made a fuss over“nothing”.  

Well, nothing except a myocardial infarction. . .

So heart patients start off with at least two important questions for the medical profession here:

1. Are my 12-lead ECG electrodes placed where they should be?
2. Does the person interpreting my ECG know how to accurately interpret this test ?

Here’s more on CHEST electrode placement (if you’re a man)*

In women, leads V3-V6 should be placed under your left breast.  Nipples should not be used as reference points in placing electrodes on men or women because – as we all know – nipple locations vary so much from person to person. General Electric Healthcare (which manufactures ECG equipment) suggests in its report called ECG Best Practices for ECG Placement on Women that not only can anatomical differences complicate correct ECG placement on women compared to our male counterparts, but“fears or embarrassment about exposing female patients’ breast tissue can increase errors in ECG lead placement.”  You should lie as still and as quietly as possible to help prevent miscellaneous “artifact” (interference) during your procedure.  Cell phones and your other non-essential devices should be placed well away from you. Any clinical signs during the test (e.g. chest pain) should be recorded by the person doing your ECG. Your privacy and dignity should be protected by draping you with a sheet to minimize exposure.

The four arm and leg placements of ECG electrodes have some wiggle room.  In the arms, an electrode can be placed anywhere between the shoulder and elbow on each side (although some sources specify wrists); in the legs, anywhere below the torso and above the ankle on each side (although some sources specify ankles). 

What I also wonder about, besides appropriate electrode placement, are the false negative ECGs (like my first one in Emergency) that are misinterpreted as “normal” – increasing the dangerous risk of that ECG (like my first one) resulting in a dismissed heart attack. Personally, this is far more worrisome to me (and arguably more dangerous!) than being referred for an unnecessary stress test based on false positives.

I wrote here about this danger in a tragically true example of dueling hospital physicians who could not agree on the interpretation of a patient’s ECG. In this case, the deadly tragedy was the preventable death of a 70-year old woman who arrived at Emergency with textbook cardiac symptoms she’d been experiencing for five days. She died after waiting 2 1/2 hours in that Emergency Department while Emergency physicians argued with cardiologists about whether she was sick enough to treat. This horrific example is a case study described by Emergency physician Dr. Pendell Myers of Charlotte, NC,  published on Dr. Stephen Smith’s ECG blog (including expert analysis of this kind of ‘what went wrong?’  cardiac case). 

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1. Rehman M,  Rehman NU. “Precordial ECG Lead Mis-positioning:  Its Incidence and Estimated Cost to Healthcare”. Cureus. 2020 Jul 7;12(7)

2. Walsh B, Smith SW, Sifford D, et al. “Examples of precordial 12-lead electrocardiogram lead placement found on Google images are often incorrect and lack gender and racial diversity.” Source.

3. New Choice Health: “Cardiovascular stress test cost and procedure information.” May 2019

4. Cook DA et al. “Accuracy of Physicians’ Electrocardiogram Interpretations”. JAMA Intern Med. 2020; 180(11):1461–14

 

ECG images courtesy of Cables and Sensors and GE Healthcare; other resources: Mayo Clinic,  Medline Plus,  Dr. Smith’s ECG Blog,  Emergency Medicine Cases

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Q:  How would you describe your own ECG/EKG test experiences?

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ANOTHER NOTE FROM CAROLYN:   I wrote much more about cardiac diagnosis and misdiagnosis in my book, A Woman’s Guide to Living with Heart Disease (Johns Hopkins University Press). You can ask for it at your local library or favourite bookshop (please support your local independent booksellers) or order it online (paperback, hardcover or e-book) at Amazon – or order it directly from my publisher (use their code HTWN to save 30% off the list price).

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See also:

If you’re a closet ECG nerd, keen on learning more about those mysterious ECG squiggles, you might check out the following links:

– Emergency Medicine Cases – “Misdiagnosis from Lead Misplacement, Artifact and Lead Reversal” by Toronto Emergency physician Dr. Jesse McLaren, March 2022 (scroll down to read the follow up explanations of a number of case quizzes)

– Life in the Fast Lane:  a 5-part ECG Basics video presentations by Dr. Theo Sklavos and Dr. William Wang – meant for medical/nursing/paramedicine students – plus any experienced docs who need a good refresher on interpreting ECGs.

– Almost any page on Dr. Stephen Smith’s ECG blog. This is where people who love electrocardiograms come to hang out with other experts. Some describe themselves as ECG hobbyists. I only hope to have an ECG hobbyist doing my next ECG. . .