Tuesday, June 28, 2011

Would you activate the cath lab prehospital?

 A 54 yo with history of hypertension awoke in the AM with substernal chest pain.  It did not abate, so at 0930, he called 911.

Medics arrived and recorded this ECG:
There is sinus tachycardia at 105 bpm.  Leads II, III, and aVF have very minimal r-waves and rather large T-waves, with straightening of the ST segments.  Leads V4-V6 have greater than 1 mm of ST elevation at the J-point (abnormal), as well as large T-waves.  V1-V3 are unremarkable except for low voltage in V1 and V2.  There is upward concavity in all leads.  There is only very subtle reciprocal ST depression in aVL, with T-wave inversion.  This helps to make the diagnosis of inferior MI.

This is highly suggestive of acute inferolateral STEMI, though not classic.  By any millimeter criteria, one would have to call it STEMI.  I would call it STEMI but it is not obvious.  [Also, tachycardia should always alert you to impending cardiogenic shock, or to possibly another diagnosis such as pulmonary embolism; however, this has none of the other classic findings of PE.]

Our prehospital protocol is:
--If a patient has chest pain and the computer algorithm reads ***Acute MI***, then they are to activate the cath lab from the field.
--If only one of these is present, they are not to do so.

The computer algorithm made no comment on any of it.

Fortunately, our medics sometimes go outside the rules.  That is what they did here: activate the cath lab.

The patient arrived in the ED at 1022 and had this ECG recorded at 1028:
Now there is new ST elevation in V2 and V3, with Q-waves forming.  Diagnostic of anterior STEMI.  Inferior leads now have much more ST elevation.  Again, all leads have upward concavity and there is only very subtle reciprocal ST depression in aVL.

The patient was taken to the cath lab at 1039.  As he was being transferred to the cath table he had a v fib arrest.  He was defibrillated.  Angiogram showed a type III (wraparound) LAD, occluded distally (but also with an 80% diagonal stenosis), such that he was having an infero-antero-apical STEMI.  The thrombosis was opened, thrombus suctioned, and the lesion stented, with a door to balloon time of 45 minutes (thanks to prehospital activation by the medics).

Medics are getting very good at reading the ECG; maybe it is time to let them overrule the computer? --This requires a formal study.  

General methods:

Take one or more EMS service(s) in which medics are well trained in reading the 12-lead. Search for all patients who had a prehospital ECG.  Find the cath outcome, or troponin outcome if no MI.  Find the computer read on the ECG.  Have 2-4 medics read the ECG blinded to the computer and the outcome.  Compare.


  1. Our service area has 4 different ALS services activating STEMI's: 3 use the medic and 1 uses the computer plus the medic. They already critique and classify activations, next step would be the blinded ECG reading. I would be interested to see how well we do at cold reads.

  2. Wow, this is the best site I’ve ever read. Thank you for sharing this.clinical research in india

  3. Great case as usual Dr. Smith... i do have a question about aVL... it is hard in the prehospital ECG due to the wandering baseline, but in the ED 12 lead, it seems that there may be some subtle ST depression of 0.5-1 mm in the setting of a small voltage QRS... Am i over-reading that? due to the ST elevation in the inferior leads, i was looking for some depression in aVL...

    thanks as usual,
    Dave B

  4. I think you're right and I will edit the post!

  5. I'm a 3rd year EM resident out of Akron, Ohio, and I just completed this very study with 30 EMS agencies and over 450 paramedics. I'm in the editing stage of the manuscript, but look for it hopefully in Prehospital Care in the next few months. In the end, the overall sensitivity and specificity of the paramedics reading ECGs was low enough that I wouldn't rely on them alone, but they can do better than most people think.

    Great case as usual Dr. Smith.

  6. That's great! I look forward to seeing the full study. Accepted? In proof stage? Did you ever publish an abstract or present at a meeting?

  7. I presented it as a poster at the National Association for EMS Physicians this last winter in Bonita Springs, Florida. The abstract was published at their conference there in the Prehospital Emergency Care Annual Meeting report.

  8. not nitpicking - were they able to get a tracing with a better baseline?


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