Posterior Myocardial Infarction: How Accurate is the Flipped ECG Trick?

Posterior Myocardial Infarction: How Accurate is the Flipped ECG Trick?

2016-11-11T19:02:45+00:00

Mirror ImagePosterior myocardial infarction (MI) represents 3.3 – 21% of all acute MIs and can be difficult to diagnose by the standard precordial leads. Typically, leads V7 – V9 are needed to diagnose this entity. Luckily, leads V1 – V3, directly face the posterior wall of the left ventricle and are the “mirror image” of the posterior wall of the left ventricle.

What is the significance of ST depression in leads V1 – V3?

This suggests that there is evidence of:

  • Anterior wall ischemia, or
  • Posterior wall MI

What are ECG criteria for posterior MI on the standard 12-lead ECG? 1

  • R/S wave ratio >1.0 in lead V2
  • Co-existing acute, inferior, and/or lateral MI
  • Limited to leads V1 – V3:
  1. ST-segment depression (horizontal moreso than downsloping or upsloping)
  2. Prominent R wave
  3. Prominent, upright T wave
  4. Combination of horizontal ST-segment depression with upright T wave

What is the correct placement of leads V7 – V9? 2

  • V7: posterior axillary line
  • V8: inferior angle of the scapula
  • V9: just to the lateral to the vertebrae

Posterior Leads

How is the “Flip Test” Performed?

  1. Get a standard 12 lead ECG
  2. Turn it over 180 degrees to look at the back of the upside-down paper.
  3. Aim the paper at a bright light source to enable seeing the “flipped” tracings.
  4. ST elevation in these leads V1 – V3 with Q waves is consistent with posterior STEMI
Posterior MI

Standard 12-lead ECG with abnormal findings circled in red

Flipped Posterior MI

Same flipped 12-lead ECG with same V1-V3 abnormality highlighted in red circles.

Posterior MI: Anterior R waves versus Posterior Q waves on ECG

With a posterior MI, R waves in the anterior leads (V1 – V3) and Q waves in the posterior leads (V7 – V9) can be present, but how good is the correlation between the two? In a case series of 58 patients with posterior MIs 3 :

  • 44.4% of patients had anterior lead R waves
  • 44.4% of patients had posterior lead Q waves
  • Only 50% of patients with posterior MI had both

Conclusion: There is poor correlation between anterior R waves and posterior Q waves.

Posterior MI: Anterior ST-depression versus Posterior ST elevation on ECG

Again with posterior MI, ST-depressions in the anterior leads (V1 – V3) and ST-elevations in the posterior leads (V7 – V9) can be present, but how good is the correlation between the two? In case series of posterior MIs:

  • 61 – 91.67% had ST depression in anterior leads 3,4
  • 91 – 100% had ST elevation in posterior leads 3,4
  • 84.6% of patients with posterior MI had both anterior ST-depressions and posterior ST-elevations 3

Conclusion

A cheap and easy way to diagnose a posterior MI is flipping the ECG over and looking at leads V1 – V3 in the light, but using posterior leads (V7 – V9) will more accurately diagnose patients with posterior MI.

I would like to thank Dr. Gemma Morabito (@MedEmIt) for the idea of this post and Amal Mattu (@amalmattu) for these ECGs.

1.
van G, Verheugt F, Meursing B, Oude O. Posterior myocardial infarction: the dark side of the moon. Neth Heart J. 2007;15(1):16-21. [PubMed]
2.
Lindridge J. True posterior myocardial infarction: the importance of leads V7-V9. Emerg Med J. 2009;26(6):456-457. [PubMed]
3.
Agarwal J, Khaw K, Aurignac F, LoCurto A. Importance of posterior chest leads in patients with suspected myocardial infarction, but nondiagnostic, routine 12-lead electrocardiogram. Am J Cardiol. 1999;83(3):323-326. [PubMed]
4.
Matetzky S, Freimark D, Feinberg M, et al. Acute myocardial infarction with isolated ST-segment elevation in posterior chest leads V7-9: “hidden” ST-segment elevations revealing acute posterior infarction. J Am Coll Cardiol. 1999;34(3):748-753. [PubMed]

Salim Rezaie, MD

Salim Rezaie, MD

ALiEM Associate Editor
Clinical Assistant Professor of EM and IM
University of Texas Health Science Center at San Antonio
Founder, Editor, Author of R.E.B.E.L. EM and REBEL Reviews
  • Anthony

    Could we just move our precordial leads off a standard 12-lead, to the posterior side? IE, V4-6 for v7-9.

    • Salim R. Rezaie

      Hello Anthony,
      Exactly. If suspicious for Posterior MI, according to the literature, the best tool is to use V7 – V9. The usual way this is done is leads V4 – V6 are made into leads V7 – V9. When you “Flip the ECG,” obviously you are looking at leads V1 – V3 because these are the leads directly opposite the posterior wall of the LV.

      Salim

  • Gemma Morabito

    The idea came from a very old post of Richard Nunez in the early years of http://www.emedhome.com

  • Stephen Smith

    Salim,

    Great topic!

    The diagnosis is much more complex than it may first appear, and I have seen many false positive cath lab activations for posterior STEMI, and many misses as well. Unfortunately, there have been no good prospective studies on the exact significance of precordial ST depression, how well location of ST Depression localizes the lesion, the best interpretation of posterior ST elevation, or the significance of upright or inverted T-waves.

    Importantly, the diagnostic cutoff of ST elevation, though imperfect, and derived primarily by a study using angiographic balloon occlusion, is only 0.5 mm for leads V7-V9. I have outlined the complexities of this diagnosis in the post below.

    If you want to activate the cath lab, or give thrombolytics, with high sensitivity and specificity, I recommend you read it along with “The 5 Primary Patterns of Ischemic ST Depression”!

    http://hqmeded-ecg.blogspot.com/2009/04/pure-isolated-posterior-stemi-not-so.html

    http://hqmeded-ecg.blogspot.com/2012/02/five-primary-patterns-of-ischemic-st.html

    Steve Smith of Dr. Smith’s ECG Blog

    • Michelle

      Hi Steve: Thanks for thoughtful comments as per usual. I hadn’t heard of 0.5 mm as a diagnostic STE cutoff for V7-V9 although this makes sense. As much I keep learning about ECG’s and its subtleties, I keep finding that there’s SO much more to learn! Keep up the great work on your site.

    • Salim R. Rezaie

      Hello Dr. Smith,
      First of all thank you for taking the time to read the post and visit the site. For people reading this reply, if you haven’t yet, you need to visit Dr. Smith’s website for ECGs. It is one of the most amazing ECG sites I have ever been on.
      I realized the lack of good data on posterior MI, as I was preparing this post. Fantastic posts, I just finished reading both. As always thank you for everything you are doing in education. Both yourself and Dr. Mattu have helped me in finding this niche of ECGs.

      Salim