Posterior OMI

Isolated posterior OMI is very rare (~5%); it is commonly associated with lateral or inferior infarcts. The posterior segment is not directly visualized on the standard 12-lead EKG, so one must rely on findings in the anterior leads to possibly diagnose posterior OMI. Findings concerning for posterior OMI:

flat ST depression
tall R wave (equivalent of posterior Q wave)
upright T wave

NOMIs do not localize to areas of an EKG. NOMIs commonly have inverted T waves and ST depression extends to V4-V6 as well as the limb leads. Additionally, the maximum ST depression in an NOMI is usually V4-V6, as opposed to V2-V5 in posterior OMI.

Posterior OMI

NOMI

The majority of posterior OMI will be in associated with the 'dominant' system. This is determined by whether or not the RCA or LCX arteries supply the posterior segments. If the LCX supplies it, it is noted to be a left-dominant system.

Examples:

One can directly visualize the posterior segments by obtaining posterior leads on an EKG. This is typically done by moving V4-V6 to the posterior chest. Given the distance to the heart, one can diagnose posterior OMI with ST elevation only 0.5mm. Similar to right-sided leads, one needs to physically mark the lead changes on the 12-lead.