Saturday, January 18, 2020

ECG Blog #171 (Culprit Artery - Repolarization Variant vs OMI - Mirror-Image)

The only information provided on the patient whose ECG is shown in Figure-1 — was that the patient was a 54-year old man. NO history was available.
  • IF this tracing was in your “pile-of-ECGs-to-be-read” — What would you do?

Figure-1: 12-lead ECG obtained on a 54-year old man. NO history available. What are your thoughts? (See text). NOTE — Enlarge by clicking on the Figure.

Descriptive Analysis:
  • Rate & Rhythm — The rhythm is sinus bradycardia at a rate between 55-60/minute.
  • Intervals — The PR, QRS and QTc intervals are all normal. If anything, the QTc is relatively short (I measure ~380 msec).
  • Axis — The mean QRS axis is normal (about +75 degrees).
  • Chamber Enlargement — None.
Looking next at Q-R-S-Changes:
  • Q Waves — Small and narrow q waves are seen in the infero-lateral leads (ie, leads II,III,aVF; and V4-thru-V6).
  • R Wave Progression — Transition occurs normally (here, between leads V2-to-V3) — albeit the R wave in lead V2 has already become relatively tall (~7 mm).

Regarding ST-T Wave Changes:
  • There is 1-1.5 mm of concave-up ST elevation in each of the inferior leads (ie, leads II,III,aVF). The mirror-image opposite ST-T wave picture of what we see in lead III appears in lead aVL. In addition — there appears to be 1 mm of flat ST segment depression in lead I.
  • In the chest leads — there is ~1.5 mm of J-point ST depression in lead V2. As has been previously mentioned — this occurs in association with an R wave in lead V2 that is already surprisingly tall (~7 mm).

Figure-2: Schematic representation of mirror-image relationships from Figure-1 (See text).

Putting IAll Together: The KEYS to interpreting this tracing lie with appreciating several mirror-image relationships (Figure-2):
  • When ST segment elevation in the inferior leads is acute — there is an almost “magic” mirror-image relationship between the way the ST-T wave looks in lead III, compared to lead aVL. These 2 leads are nearly 180 degrees opposed to one another — therefore they show reciprocal changes.
  • Note in Figure-2 — how the mirror-image of the ST-T wave in lead aVL (within the light BLUE insert) — looks identical to the shape of the elevated ST-T wave in lead III (within the WHITE rectangle).
  • Similarly, the mirror-image of the elevated ST-T wave in lead III (within the light BLUE insert) — looks identical to the shape of the inverted ST-T wave in lead aVL (within the WHITE rectangle).
  • Confirmation that the above mirror-image relationships are real and represent an acute change consistent with acute inferior MI — is forthcoming from the clearly abnormal shelf-like ST depression we see in lead I.
  • Further support of recent (if not ongoing acuteocclusion of the RCA (Right Coronary Artery) — is suggested by the positive Mirror Test we see for the QRST complex in lead V2 (For more on the Mirror Test See ECG Blog #80). Anterior leads (ie, leads V1, V2 and/or V3) often manifest the mirror-image opposite picture of ongoing events in the left ventricular posterior wall — and the mirror-image of the QRST complex in lead V2 (within the light BLUE insert) shows a large Q wave + downward coved ST elevation, that leads to beginning T wave inversion.

BOTTOM Line: One has to interpret the ECG in Figure-1 as consistent with recent (if not ongoing acute) RCA occlusion until proven otherwise. Since this tracing was in your “pile-of-ECGs-to-be-read” — the responsibility falls on YOU to immediately look up the patient to find out WHAT is going on?
  • In addition to acute infero-postero MI — there may also be acute RV involvement in Figure-1 — since rather than ST depression, the ST segment in lead V1 is not at all depressed as would be expected with acute posterior MI. That said — right-sided chest leads would be needed to know for certain if there is or is not associated acute RV involvement.

P.S.  Unfortunately — follow-up in this case is lacking. The patient was seen years ago — and I have no further information on the case. Nevertheless, I thought it worthwhile to discuss how even when no clinical information is available — how the mirror-image opposite relationships we see in this tracing tell us we have to assume these ECG changes are acute until we prove otherwise.

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