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:
- ST-segment depression (horizontal moreso than downsloping or upsloping)
- Prominent R wave
- Prominent, upright T wave
- 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
How is the “Flip Test” Performed?
- Get a standard 12 lead ECG
- Turn it over 180 degrees to look at the back of the upside-down paper.
- Aim the paper at a bright light source to enable seeing the “flipped” tracings.
- ST elevation in these leads V1 – V3 with Q waves is consistent with posterior STEMI
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.
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