ECG Interpretation Review - #7 (Infarction, ECG Changes, Inferior, Posterior, Lateral, Anterior MI)

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QUESTION: Interpret the 12-lead ECG below, obtained from a patient with new-onset severe chest pain.

• How many abnormal findings can you identify?
• What areas of the heart are involved?

Figure 1 — ECG from a patient with new-onset chest pain (See text).

INTERPRETATION:  The rhythm is sinus at 75/minute.  All intervals are normal.  We estimate the axis at +60 degrees.  There is no chamber enlargement.

• Q-R-S-T Changes: There are fairly large Q waves in the inferior leads, and smaller q waves in V5,V6.  Transition occurs normally between leads V3-to-V4 (Did you notice slight loss of R wave fromV2 to V3? )
• There is hyperacute ST segment elevation in leads III and aVF.  By the concept of "patterns-of-leads" (ie, simultaneously looking at all leads in a given lead group) — there is probably also some ST elevation in lead II.  There are reciprocal changes (ST depression/T wave inversion) in the anterolateral leads.

CLINICAL IMPRESSION:  This ECG suggests acute inferior MI, with development of Q waves, ST elevation, and extensive reciprocal changes.  List #5 (Figure 2) suggests that in addition to reciprocal changes, the T wave inversion in leads V2,V3 could also be due to associated posterior MI and/or concomitant anterior ischemia (Note how the depressed ST segment pattern in leads I and aVL is virtually the mirror image of the ST elevation in leads III and aVF — ergo, true "reciprocal" changes!).

Figure 2 - Causes of Anterior ST Depression with Inferior MI.

ADDITIONAL POINTS:  Given the history (new-onset chest pain) and the ECG picture seen in Figure 1 - this patient is clearly a good potential candidate for acute intervention.

• Finally — Subtle but real loss of R wave (from V2-to-V3) could be due to lead placement error or it could reflect loss of anterior forces from acute MI.

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