Tuesday, January 14, 2020

ECG Blog #170 (Atypical Chest Pain - Mirror Image - Troponin - Lcx - Lad)

The ECG in Figure-1 was obtained from a 30-year old man with an unusual story. He was admitted to the hospital to “Rule Out MI” — with what was described as “atypical” chest pain, that was not thought to be cardiac in etiology. Serial troponins were negative. His initial ECG (not shown) was interpreted by a capable emergency physician as “normal”. The patient had a normal Stress Echo, in which he attained his target heart rate and showed no wall motion abnormality. He was about to be discharged from the hospital with a diagnosis of atypical non-cardiac chest pain. His pre-discharge ECG ( = ECG #2) is shown in Figure-1. There were no new symptoms at the time ECG #2 was done. How would you interpret this pre-discharge ECG ( = ECG #2)?
  • What would you do, given that all testing to this point had been normal?

Figure-1: This is the follow-up ECG, obtained on this 30-year old man who was about to be discharged from the hospital. His initial ECG (not shown) was interpreted as “normal”. Serial troponins, and Stress Echo were completely normal (See text).

COMMENT: We can’t comment on the initial ECG — since it is not shown. What we can say — is that ECG #2 is not a normal tracing! Presumably, had the initial ECG been as abnormal as this 2nd ECG — the capable clinician who interpreted that initial tracing would presumably have at least seen some of the abnormalities — BUT — We can’t comment on what we are not shown ...

Descriptive Analysis of ECG #2:
  • Rate & Rhythm — It’s hard to be certain what the cardiac rhythm is! This is clearly a supraventricular rhythm — because the QRS complex is decidedly narrow. But there is no long lead rhythm strip. The R-R interval is not completely regular. It looks like there is atrial activity in front of some QRS complexes — but a clearly upright P wave is lacking in lead II. I’d guess this is an ectopic atrial rhythm, perhaps with some junctional escape beats — but I can’t rule out the possibility of a nearly regular AFib. A longer period of monitoring is clearly needed to determine for certain ... Bottom Line: The above said — Since the rhythm is supraventricular, we can assess ST-T waves in ECG #2 for potential ischemic changes!
  • Intervals — The PR interval is irrelevant in this tracing — since we don’t see consistent atrial activity. As noted — the QRS complex is narrow. The QTc interval appears to be normal.
  • Axis — The mean QRS axis is normal (about +25 degrees).
  • Chamber Enlargement — None.

Looking next at Q-R-S-Changes:
  • Q Waves — Small and narrow q waves are seen in high lateral leads I and aVL.
  • R Wave Progression — Transition occurs normally (here, between leads V2-to-V3) — albeit abruptly (ie, the QRS was almost all negative in lead V2 — and abruptly becomes almost all positive by lead V3).
  • Regarding ST-T Wave Changes:
  • There is 1-2mm of concave-up ST elevation in leads I and aVL. The mirror-image opposite ST-T wave picture of what we see in lead aVL appears in lead III. Of note — there is ~2mm of J-point ST depression in lead III — and 1-1.5mm of J-point ST depression in leads II and aVF.
  • The ST-T wave in lead V2 is somewhat distorted by artifact (ie, the contour of the ST segment in V2 is not at all smooth). That said — the T wave looks disproportionately peaked in V2, with a disproportionately wide base — however, other than nonspecific ST-T wave flattening in leads V4-thru-V6, there do not appear to be acute changes in the remaining chest leads.

Putting IAll Together: The limb leads in ECG #2 are clearly abnormal. ST elevation in high-lateral leads — with a mirror-image opposite appearance of the ST-T in lead aVcompared to lead III should suggest an acute cardiac event until you prove otherwise (For more on this point — Please see My Comment at the bottom of the page in the 10/6/2018 SSmith ECG Blog post).

Follow-Up on This Case: Based on the abnormal pre-discharge ECG in Figure-1 — the cardiologist took this patient to the cath lab. He was found to have a very tight stenosis of a dominant LCx (Left Circumflex) coronary artery — which was successfully stented.
  • It is fortunate that this pre-discharge ECG was obtained and interpreted before sending this patient home.
  • Learning Point: The initial ECG in a patient with significant coronary disease may not always be abnormal. Serial troponins and stress testing may also be normal. None of this rules out the possibility of severe underlying coronary disease.

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