Monday, August 23, 2021

ECG Blog #246 (60) — What is the Mirror Test?

Imagine that the ECG in Figure-1 was obtained from an older patient with epigastric discomfort and "heartburn". No prior tracing is available for comparison.



  • How would you interpret the ECG in Figure-1?
  • Where is the problem?


Figure-1: ECG obtained from an older patient with epigastric discomfort and "heartburn". WHERE is the problem?



NOTE: Some readers may prefer at this point to listen to the 8:30-minute ECG Audio PEARL before reading My Thoughts regarding the ECG in Figure-1. Feel free at any time to refer to My Thoughts on this tracing (that appear below ECG MP-60).



Today's ECG Media PEARL #60 (8:30 minutes Audio) — Reviews use of the "Mirror Test" to facilitate recognition of: i) Acute Posterior MI; ii) Acute High-Lateral or Inferior MI (ie, the "magical" reciprocal relationship between leads III and aVL)andiii) Anterior ST elevation due to LVH (that is not indicative of anterior MI).

  • NOTE: I've added LINKS to related ECG blog posts to better illustrate the concepts put forth in today's Audio Pearl (These LINKS are shown below at the end of this blog post).




MY Sequential Thoughts on the ECG in Figure-1:

As always — I favor the use of a Systematic Approach (which I review in ECG Blog #205):

  • Rate & Rhythm: The P wave is upright in lead II — so the rhythm in Figure-1 is sinus tachycardia at ~105/minute. 
  • Intervals (PR/QRS/QTc): The PR interval is normal — the QRS complex is narrow — and, the QTc appears slightly prolonged (albeit difficult to assess the QTc interval when the heart rate is faster than 90-100/minute).
  • Axis: There is a leftward axis — as determined by almost complete negativity of the QRS in lead aVF. I'd estimate the frontal plane axis at -30 degrees, as the QRS complex in lead II is approximately equiphasic (ie, equal parts positive and negative).
  • Chamber Enlargement: None. Instead — there is low voltage in the limb leads (ie, none of the 6 limb leads measure more than 5 mm).


Regarding Q-R-S-T Changes:

  • Q Waves — There are large Q waves in each of the inferior leads (ie, in leads II, III and aVF). There are also deeper-than-expected Q waves in leads V4, V5 and V6. And, there is a tiny-but-present initial q wave in lead V3 that simply should not be there (ie, normal septal q waves are uncommon in lead V4, and they should not be seen in lead V3).
  • R Wave Progression — Transition (where the R wave becomes taller than the S wave is deep) occurs early, between leads V1-to-V2 (Transition normally occurs between leads V2-to-V4).
  • ST-T Wave Changes — There is slight-but-real ST elevation in each of the inferior leads. There is also very subtle ST elevation in lead V6. ST segments are flat (if not, slightly depressed) in leads I, aVL and V5. There is ST depression in leads V1-thru-V4, with maximal ST depression in leads V2 and V3.


Putting It All Together: The ECG in Figure-1 strongly suggests there has been recent (if not acute) infero-postero-lateral OMI ( = Occlusion-based Myocardial Infarction). I'll add the following important points:

  • It's impossible to date the MI in today's case. The fact that Q waves in each of the inferior leads are deep would seem to favor a less acute onset. No R wave at all is seen in lead III — and no more than the tiniest of r waves is seen in lead aVF. That said — on occasion, significant Q waves have been known to form in as little as 1-to-2 hours. In addition — it is entirely possible that this older patient had a previous inferior infarction — and is now having acute reinfarction of the inferior wall. Bottom Line: We can not rule out the possibility of a very recent, or even acute ongoing infarction simply on the basis of the large size of inferior Q waves.
  • In favor of a more recent onset for the inferior lead changes is the fact that coved ST elevation persists in each of the 3 inferior leads. While the shape and amount of ST elevation in leads III and aVF looks to be less acute (and is more consistent with an older event) — the shape and amount of ST elevation in lead II is clearly of more concern (especially considering modest amplitude of the R wave in this lead). Although minimal in amount — the shape of the scooped ST segment in lead aVL is potentially consistent with a reciprocalchange with respect to the ST segment shape in lead III.
  • In lead V6 — there is a relatively large Q wave — a slightly coved, and perhaps ever-so-slightly elevated ST segment — with beginning T wave inversion. Given the ECG changes just described in the limb leads, this suggests there has been lateral infarction, albeit of an indeterminate age.
  • We are not told when symptoms began for the patient in today's case. This is yet another factor that makes determination of the "age" of infarction difficult.

  • PEARL #1: It is the ST depression in leads V1-thru-V4 (which is maximal in leads V2 and V3) that raises greatest concern for a posterior infarction in today's case that must be assumed acute and ongoing until proven otherwise. 


  • Did YOU notice the positive "Mirror" Test? (See Figure-2).

Figure-2: Illustration of a positive Mirror Test for the ECG that was shown in Figure-1 (See text).

The Positive Mirror Test in Figure-2:

As discussed in detail in Audio Pearl #60 (above) — the Mirror Test is used as a visual aid to facilitate recognition of acute posterior MI. The principle of this test is simple: It is based on the fact that the mirror-image view of anterior leads provides insight to the nature of electrical activity as viewed by the posterior wall of the left ventricle.

  • Note that I have vertically flipped anterior leads V1, V2 and V3 in the far right portion of Figure-2 (the mirror-image view of these 3 leads is outlined in RED). The shape of the ST depression seen in leads V1V2 and V3 of Figure-2, when vertically flipped (as viewed in the Mirror Test) suggests deepening Q waves — worrisome shape and amount of ST elevation — and already deep T wave inversion.
  • PEARL #2: The finding of ST depression that localizes to the anterior leads, and which is maximal in leads V2 and/or V3 — strongly suggests posterior infarction that may be acute. Many providers equate the picture of ST-T wave changes that we see in the anterior leads of Figure-2 as a "STEMI-equivalent" — since this ECG pattern is equally indicative of acute OMI in need prompt reperfusion, as is an acute MI in which there is ST elevation (Please see ECG Blog #193including Audio Pearl #10 in that blog post — for detailed discussion on the concept and clinical implications of diagnosing acute OMI).
  • NOTE: Early transition (ie, development of an R wave taller than the S wave is deep already by lead V2supports the diagnosis of posterior infarction in Figure-2. In the Mirror Test — the taller R waves become in anterior leads V1, V2 and V3 — the deeper the Q waves these R waves become when these anterior leads are vertically flipped.

PEARL #3: Did YOU notice the fragmented QRS complexes in leads III and aVF of Figure-2? Although obvious that there has been inferior infarction at some point (ie, from the depth of the inferior Q waves — and the loss of R wave amplitude in these leads) — fragmentation of the inferior Q waves in leads III and aVF is yet one more indication of "scar" (and in this case, of prior infarction)



Conclusion to Today's Case:

The patient in today's case presented with epigarstric discomfort and "heartburn". Especially in an older patient — this history certainly could be consistent with symptoms of an acute cardiac event. ECG findings of concern include sinus tachycardia — infero-lateral infarction of uncertain age (with residual ST elevation) — andposterior infarction marked by a positive Mirror Test with localized anterior ST depression that is maximal in leads V2 and V3. 

  • An acute ongoing event should be assumed until proven otherwise. Ideally — prompt cath for diagnosis and potential reperfusion should be performed.




Related ECG Blog Posts to Today’s Case:

  • ECG Blog #205 — Reviews my Systematic Approach to 12-lead ECG Interpretation.
  • ECG Blog #193 — illustrates use of the Mirror Test to facilitate recognition of acute Posterior MI. This blog post reviews the basics for predicting the "culprit artery". NOTE: Figure-5 in the Addendum of this blog post illustrates the essentials for identifying an isolated posterior MI.
  • ECG Blog #184 — illustrates the "magical" mirror-image opposite relationship with acute ischemia between lead III and lead aVL (featured in Audio Pearl #2 in this blog post)
  • ECG Blog #167 — another case of the "magical" mirror-image opposite relationship between lead III and lead aVL that confirmed acute OMI.
  • ECG Blog #245 — Reviews the ECG diagnosis of LVH, including CAVEATS that may complicate assessment of associated acute ischemia.
  • The September 21, 2020 post in Dr. Smith's ECG Blog — My Comment (at the bottom of the page) emphasizes utility of the Mirror Test for diagnosis of acute Posterior MI.
  • The February 16, 2019 post in Dr. Smith's ECG Blog — My Comment (at the bottom of the page) emphasizes utility of the Mirror Test for diagnosis of acute Posterior MI
  • The March 29, 2019 post in Dr. Smith's ECG Blog — My Comment regarding Tracing A (at the bottom of the page) illustrates how LVH is a common mimic of acute ischemia.
  • The March 31, 2019 post in Dr. Smith's ECG Blog — My Comment (at the bottom of the page) illustrates the potentially misleading effect the pre-hospital ECG may have in patients with LVH, by cutting off S wave voltage in the anterior leads.
  • The December 27, 2018 post in Dr. Smith's ECG Blog — My Comment (at the bottom of the page) illustrates a case with anterior ST elevation from LVH that may falsely suggest acute anterior infarction. 

  • ECG Blog #80 — reviews prediction of the "culprit" artery (and provides another case illustrating the Mirror Test for diagnosis of acute Posterior MI).


ADDENDUM (8/23/2021): I've added below in Figure-3 review of a case in which there is an isolated posterior MI (ie, without accompanying inferor lead ST elevation).



Figure-3: KEY points in the recognition of isolated posterior MI (This figure is taken from ECG Blog #193 — in which I review the "Basics" for predicting the "culprit" artery).

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