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ECG Findings

  • ST-segment depression in leads V1-V3

  • Upright T waves in V1-V3

  • Tall R waves with an R-wave/S-wave ratio greater than 1 in lead V1-V3, most often seen in V2-V3, developing over the course of hours


  1. Note that some authors refer to “posterior” infarction as “inferolateral” infarction, based on echocardiographic data that show that the involved portion of the left ventricle in question is actually inferolateral rather than truly posterior in location.

  2. This diagnosis is often missed as the posterior portion of the left ventricle has no ECG electrodes directly overlying it. This means that posterior MI will only reflect as reciprocal changes that are most common in V1-V3. Instead of ST elevations, one will find ST depressions, and instead of Q waves, one will see tall R waves.

  3. Posterior involvement may be confirmed with posterior leads. V7 is located in the left posterior axillary line; V8 is located at inferior tip of left scapula; V9 is positioned between V8 and the spine, all in the same horizontal plane as V6.

  4. Frequently, an inferior MI is also present with a posterior MI, since the right coronary artery serves both areas.


Acute Posterior Myocardial Infarction. (ECG contributor: R. Jason Thurman, MD.)


This tracing demonstrates injury in the posterior LV, manifesting as acute ST depression in V2 (arrow).


Flipping the ECG upside down and looking through the paper with a backlight shows an ST-elevation injury pattern (arrow). A posterior ECG can help distinguish between posterior STEMI and anterior ischemia.


The R-wave amplitude approximates that of the S wave (arrow), and the R-wave duration is significant (>4 ms). This is actually an “inverted Q wave” from a posterior infarction.

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