Q4 Urgent Caring- Where Mistakes Are Made, ST Segment Depression

Jerry W. Jones, MD, FACEP, FAAEM
Section Editor, ECG Corner

Let’s look at just the precordial leads of an ECG for the moment. (Figure 1)

The most notable finding on this portion of the ECG is the obvious ST depression in Leads V1 – V4. What does ST depression mean to you? Most people reply subendocardial ischemia – and they would be correct some of the time… but not all the time!

Assuming that ST depression always means subendocardial ischemia is where the mistake begins. In a nutshell – it does not always mean subendocardial ischemia! Sometimes it means acute epicardial ischemia. That’s right: exactly the same as a STEMI. And right here in Leads V1 – V3 (sometimes even Lead V4, as in this ECG) is where many such mistakes are made. OK, I always say, “Never diagnose anything from a rhythm strip or an incomplete 12-lead ECG,” so let’s see the whole ECG… 

We can see there is a lot more to this ECG than just the changes in the precordial leads, and we didn’t even discuss all the changes in the precordial leads! There is ST elevation in Leads II, III, and aVF. That strongly suggests an acute inferior wall MI. 

But we also see ST elevation in Lead I and Leads V5 and V6. We do not see ST elevation in Lead aVL and the ST elevation in Lead III is very subtle and minimal.

But let’s turn our attention back to Leads V1 – V3 specifically. So many people would see that and say, “ST depression in V1 – V3… that’s anteroseptal ischemia!” I have seen that exact scenario during my career as a teaching attending physician with some of these patients being sent home because their chest pain resolved spontaneously in the ER!

ST depression in Leads V1 – V3 occurring on the 12-lead ECG of a patient with chest pain should always make you think of an acute posterolateral MI – not subendocardial ischemia. Let’s look at an ECG with a true anteroseptal subendocardial ischemia…

This (Figure 3) is an ECG with a true anteroseptal subendocardial ischemia… and basolateral, lateral, and inferior subendocardial ischemia as well. Notice two things…

  1. With true anteroseptal subendocardial ischemia, Lead V1 often has no ST depression and, on the contrary, may have a small amount of ST elevation.
  2. Subendocardial ischemia does not localize; it’s everywhere! When you see ST depression restricted to a particular vascular area on a 12-lead ECG – recorded on a patient with chest pain – you are much more likely seeing the ST depression of a reciprocal change to an acute STEMI. And to make matters even more confusing – the reciprocal change can appear first, and it can be a lot more impressive than the primary change of ST elevation! (The ST depression in Leads V1 – V3/V4 is a reciprocal change to an acute posterolateral MI.)

Look at Leads V1 – V3 in Figure 3 again – very closely! What else can look exactly the same and can accompany an acute inferior MI? A right ventricular infarction can look exactly the same! Exactly! So, before you call this an anteroseptal subendocardial ischemia, remember you have only one out of three chances of being correct – and the other two possibilities are acute MIs!

Remember Jone’s Rule:

Any ST depression on the 12-lead ECG of a patient with chest pain compatible with an acute coronary syndrome represents a reciprocal change to a STEMI until proven otherwise.

Recommended Reading:

    1. Goldberg, HL MD, Borer, JS MD, Jacobstein, JG MD, Kluger, J MD, Scheidt, SS MD, Alonso. DR MD. Anterior S-T Segment Depression in Acute Inferior Myocardial Infarction: Indicator of Posterolateral Infarction. The American Journal of CARDIOLOGY. Volume 48; December 1981.
    2. Morris F, Brady WJ. ABC of clinical electrocardiography: Acute myocardial infarction—Part I. BMJ. Volume 324; 6 April 2002.
    3. Edhouse J, Brady WJ, Morris F. ABC of clinical electrocardiography: Acute myocardial infarction—Part II. BMJ Volume 324 20 April 2002.
    4. Shlomi Matetzky, MD, Dov Freimark, MD, Micha S. Feinberg, MD, Ilya Novikov, PhD, et al. Acute Myocardial Infarction With Isolated ST-Segment Elevation in Posterior Chest Leads V7 – V9. Journal of the American College of Cardiology. Vol. 34, No. 3, 1999