What is the significance of reciprocal ST depression in STEMI?

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Reciprocal ST depression reflects opposing changes caused by a transmural ischemic injury. In STEMI, the area of infarction shows ST elevation because of the current of injury, while the opposite wall exhibits ST depression due to the vector of injury affecting the opposing leads. This pattern helps confirm acute STEMI and, by noting which leads have elevation versus depression, helps localize the involved territory (for example, inferior infarction often has reciprocal depression in the lateral leads, while anterior infarction may show reciprocal changes in the inferior leads).

It’s not a feature of pericarditis, which more commonly presents with diffuse ST elevation and PR depression rather than a localized reciprocal pattern. And reciprocal changes aren’t limited to inferior MI; they can appear with infarcts in various regions, depending on the leads involved.

So the best answer is that reciprocal ST depression supports STEMI and helps localize the infarct.