Data quality and computerized interpretive statements

There’s an important caveat when it comes to the GE-Marquette 12SL interpretive algorithm.

It’s highly susceptible to errors when it interprets ECGs with poor data quality.

Consider the following example.

I don’t know anything about the history or clinical presentation. For my purposes here, I’m only interested in the interpretive statements.

First, the rhythm strip.

This data quality isn’t that bad.

The rhythm is borderline sinus bradycardia with 1°AVB. The QRS complex appears to be “wide” and QRS morphology in lead II looks very much like RBBB is supposed to look like in lead I.

When I see something like this, I immediately check the leads to make sure the red and black electrodes are not switched.

Now the first 12 lead ECG.

This data quality is horrible could be improved.

I suspect this ECG was captured in the back of a moving ambulance. Note that the rhythm strip was captured at 0222 and the first 12 lead ECG was captured at 0255.

In the first place, had this been a STEMI, that’s 33 minutes of time during which the hospital could have been calling in the cath team from home (nights, weekends, holidays). This is sometimes referred to as “parallel processing” and it’s a key concept for prehospital 12 lead ECG programs and regional STEMI systems.

In addition, sometimes you will get wandering baseline artifact in the back of a moving ambulance.

All the more reason to capture your 12 lead ECG on scene with the first set of vital signs.

I cringe when I see an ECG like this on the Lifenet Receiving Station (all too often). This gives ammunition to ED physicians who don’t support prehospital 12 lead ECGs and are adamantly opposed to activating the cardiac cath lab while a STEMI patient is still in the field.

What does this ECG tell us?

In the first place, the heart rate is slower than in the rhythm strip. We also see obvious RBBB morphology in lead V1. Beyond that, the only leads we can really interpret are lead II and the right precordial leads.

The interpretive statement mentions “premature ectopic complexes with ventricular escape complexes”. It also says “lateral infarct, age undetermined.” Both of these statements should be completely ignored because of the poor data quality.

Let’s look at the third and final 12 lead ECG.

The data quality is still poor, and now we’re getting the ***ACUTE MI SUSPECTED*** message from the computer.

The GE-Marquette 12SL interpretive algorithm gets a bad rap, and those of you who have followed my blog from the beginning (or know me from the EKG Club and other internet forums) know that I have defended its capabilities from time to time.

It’s true that the computer has a high specificity when it gives the ***ACUTE MI SUSPECTED*** message, but only when it interprets an ECG with excellent data quality.

That point cannot be overemphasized.

The specificity can be improved even more if the patient’s chief complaint is chest pain and heart rate is less than 100.

The take-home point is this. If you get the ***ACUTE MI SUSPECTED*** message but your ECG is showing poor data quality, you should completely ignore the interpretive statement and capture another 12 lead ECG with excellent data quality.

Under no circumstances should you transmit an ECG with poor data quality to the emergency department for physician interpretation.

Earlier today I Googled “12 lead data quality” and found a document about the ZOLL M-series monitor called 12-Lead ECG Monitoring that says, “The 12SL analysis results can be affected by poor ECG data quality. If poor data quality is flagged by the system, the interpretation statements will be preceded by the statement, “Poor data quality, interpretation may be adversely affected.”

This feature must be unique to ZOLL, because I’ve never seen a similar message on the LP12.

How do you capture a 12 lead ECG with excellent data quality?

  • Undress the patient from the waist up, including the bra if it’s a female.
  • Prep the skin (shave the skin if necessary and use benzoin tincture if the patient is diaphoretic).
  • Strand out each lead individually and don’t wrap the ECG leads around the O2 or IV tubing.
  • If possible place your patient in a comfortable semi-Fowlers position.
  • Make sure the patient is not holding him/herself up with his/her arms.
  • Once the leads are placed, cover the patient with a sheet to prevent shivering.
  • Have the patient breathe normally.
  • Capture the ECG.

It’s really not that hard.

You should orchestrate all of this with the first set of vital signs.

You should also consider grabbing yourself a few gowns next time you’re at the hospital. The nurses will love you when you bring in a gowned patient with the ECG leads perfectly placed, an IV established, and the first set of labs drawn.


  • Great post with excellent points. My comments…there is a way to discreetly undress someone and reduce their anxiety in the process. I agree that patients should be undressed for an ECG, but many women are extremely modest, especially from older generations. If physically able, have the patient take off their own shirt and bra while you hold the sheet up in front of them. Keep the patient covered while you expose only the areas of the chest needed at one time while placing the ECG leads on. Patients will appreciate your professionalism while appreciating their privacy. As for shaving, due to infection risks shaving is not recommended rather the use of clippers (hospitals are no longer shaving patients for any procedure). However they may not be readily available in the ambulance. Another trick for skin prep is applying alcohol via an alcohol swab to the skin and then wiping with a towel before applying tincture of benzoin. Sometimes, the most important points in delivering quality care are the least technical. Thanks!

  • Tom B says:

    Excellent points, BarefootNurse! Thanks for the comments. I’ll try that next time I have a “modest” female patient.I should have clarified that my department uses the electric rechargeable clippers. It’s no fun shaving off somebody’s mole! And if you live in a region where they’re still giving thrombolytic therapy?Tom

  • Bob Jester says:

    Tom-I hear what you’re saying about the need for clean tracings, and preach to my co workers until they avoid me the need for good skin prep. Recently I treated a sweet old woman whose chest discomfort resolved with a nitro and 4 baby aspirin, she also had Parkinsons disease with almost constant extremity tremors. I tried limb placement with predictable results, I tried moving the electrodes to the upper arms and legs with similar failure. I resorted to placing the limb leads on the chest and abdomen and didn’t get a clear tracing until we were standing in the ED waiting for a bed that showed ST segment elevation in the inferior leads.She denied complaints of any discomfort or shortness of breath during the entire trip because as she explained to the ED staff, she “didn’t want to bother the nice men who were taking care of me”. My question is, How would you place the leads to minimize distortion from the patients extremity tremors?

  • Sonnet says:

    Dear Tom BThanks for this informative post.For me it is first time to know this item: Strand out each lead individually and don’t wrap the ECG leads around the O2 or IV tubing.One should be cautions while analyzing ECG esp. if MI is suspected.

  • Tom B says:

    Bob – Parkinsonian patients present quite a challenge! You may not be able to get a “clean” ECG. I wish I had some words of wisdom for you, but I struggle with these also.Just do the best you can and try to “read through” the artifact.Good luck!Tom

  • Tom B says:

    Sonnet – I’ve found that’s the best way to stay organized and prevent artifact on the ECG.Thanks for the comment!Tom

  • Bob Jester says:

    Fortunately the closest ED was at the same hospital as the CCL. We were 15 minutes away so we didn’t waste too much time by not having a prehospital notification. As an aside, any case that goes to the CCL without a prehospital notification automatically gets referred to our Peer Review team. It was a little different having a case of mine up for discussion.

  • Shaggy says:

    Bob, am I to assume you guys are able to make your own decision as to making the CCL your destination? Going to the cath lab without a notification? Am I reading it right or am I just a putz?

  • Shaggy says:

    BTW, I wanted to comment in your other post, but everytime I put gowns in the truck, others remove them. I too wondered about what to do with the patient regarding privacy when stripping the patient for the 12 lead. Most often, there are many family members or others present. The sheet method is real nice since I don’t have a curtain to pull behind me.

  • Bob Jester says:

    Blogger Shaggy said… Bob, am I to assume you guys are able to make your own decision as to making the CCL your destination? Going to the cath lab without a notification? Am I reading it right or am I just a putz?Right now we make the decision on conjunction with OLMC although I’ve never heard of one of them saying no to a request to initiate the one call system to alert the on call team or alert the CCL during regular duty hours. I probably could have written better. I meant cases that EMS brings in to the ED and the ED makes the decision to send the patient to the lab. We track them to assure our medics are making good decisions and as teaching cases when things don’t go exactly according to plans.

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