Approach to EKG Interpretation

Dr. Basrai
Cardiology, Emergency Medicine, Internal Medicine, Medical School, Internship, Residency

Lecture Notes

The goal of this approach is to look at the EKG from the bigger picture. What was the indication for ordering this EKG? What are the specific things I am going to look for and what interventions will I perform based on this information?

Reasons to get an EKG

  1. Is the HR too fast?

  • Is the rhythm regular or irregular? Is it a narrow or wide complex tachycardia

  • Do I need to cardiovert the patient?

       2. Is the HR too slow?

  • Is there evidence of a high-grade heart block (i.e. 2nd-degree type 2 or 3rd-degree heart block)?

  • Does the patient have a past medical history of ESRD on dialysis? If so, do I need to consider pushing calcium to treat hyperkalemia?

      3. Is my patient having an acute MI?

  • Do I need to activate the cath lab?

  • Do I need to call a cardiologist?

So how do you know if your patient is having a heart attack? In order to answer this question you must know how the EKG changes when there is 100% occlusion of a coronary artery.

Here is what you will see starting with the earliest change:

  1. Peaked T waves: These are different from the peak T waves in hyperkalemia in that they are broad based and would not hurt if you sat on them.

  2. STE into your classic tomb stone appearance

  3. Flattened or T wave inversions

  4. As everything is flattening your Q waves are getting bigger while your R waves are getting smaller until all you have is a massive Q wave.

Now that we know what to expect when there is 100% occlusion of a coronary artery we can look at each geographical area of the EKG to make sure that none of the 4 EKG changes are present.

The leads corresponding to geographical areas of the heart are:

  1. Lateral: I, aVL, V5, and V6

  2. Inferior: II, III, aVF

  3. Anterior: V1-V4

So now that we are armed with all of this information lets talk about the approach to the EKG

Step 1: Look at the rhythm strips that are either at the top or the bottom of the EKG. Really spend time looking at the entire rhythm strip asking yourself if the rhythm is too fast or too slow. If the rate is too fast, ask yourself if there is evidence of narrow or wide QRS complexes. Check with calipers to see if the rhythm is regular or irregular. If the rate is too slow, ask yourself if there is evidence of high-grade heart block.

Step 2: Look at each geographical area of the heart and ask yourself if there is evidence of:

  1. Peaked T waves

  2. STE or STD ( Add depressions here to make sure you are not missing subendocardial injury)

  3. Flattened T waves or T wave inversions

  4. Q waves

If you see something concerning like peaked T waves or TWI, try to pull up an old EKG to see if these are new. If you do not have an old EKG order a stat repeat EKG. Remember it takes a while for techs or nurses to get the repeat EKG. Hopefully, on the repeat EKG, you will start to see dynamic EKG progressions that you expect if there is complete occlusion of a coronary artery. Do not wait 4-6 hours for the repeat EKG, which is the setup in most ACS rule out order sets.

A couple of STEMI equivalents to know about are

  1. Posterior MI which will have large STD anteriorly

  2. STE in aVR which is associated with left main artery occlusion

  3. De Winter’s T Waves which is suggestive of a proximal LAD lesion. This pattern will show J point depressions followed by peaked T waves in the precordial leads

  4. Sgarbossa’s Criteria which will help identify STEMI in LBBB or pacemaker patients.

  5. Wellen’s Syndrome which represents a critical stenosis of the LAD.

For a complete review of these STEMI equivalents check out https://wikem.org/wiki/STEMI_equivalents

Finally, let’s list the differential dx for STE:

  1. STEMI

  2. Pericarditis

  3. LBBB

  4. Lt ventricular aneurysm

  5. Benign early repolarization/J point elevation

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