As we reflect on the year 2012, it is important to know what does not "reflect" (corny stretch) in the world of EKGs. Fifty percent of anterior STEMIs lack reciprocal changes. This is crazy but a fact. I will try to summarize why this occurs, but you may want to read the attached article.
We have all learned that reciprocal changes are important in diagnosing STEMIs, and their presence increases the likelihood that the EKG pattern is secondary to coronary occlusion. Further this concept of reciprocal changes is the main focus of my "Swans Reflecting Elephants" talk, whereby localized ST depression is invariably secondary to subtle STEMIs.
But does the absence of reciprocal change rule out MI? The answer is no. As stated above, 50% of anterior STEMIs lack reciprocal changes.
That said, inferior STEMIs will almost always have STD (albeit may be subtle) in I/AVL or at least new TWI in AVL. Lateral STEMIs also will have reciprocal change.
The pathophysiology of inferior ST segment changes in the setting of anterior STEMI is actually pretty cool. I have read a lot on this, and I think you will like this article I am attaching. To summarize, in the setting of anterior STEMIs there are 3 patterns of inferior ST segment changes, [a] ST depression, [b] ST elevation, and [c] No ST change. Group "c" accounts for 50%, quoted many times in the literature.
Look at Figures 1, 2, and 3 in the paper, as this is the best explanation on this issue that I have found.
-- Anterior STEMI with inferior ST depression occurs because the occlusion is proximal LAD (proximal to D1 or 1st diagonal), with infarction extending to high lateral wall. Thus the inferior ST depression actually represents true reciprocal change from lateral ischemia. Anterolateral STEMI.
-- Anterior STEMI with inferior ST elevation occurs the the occlusion is distal to D1 AND wrap-around LAD (a variant) that supplies the inferior wall, thus causing inferior STEMI.
-- Anterior STEMI with no inferior ST changes occur in 2 settings, which is exemplified in example #3 in the paper. [1] Occlusion distal to D1 with no wrap-around LAD, so no infarction of lateral (distal) or inferior (no wrap-around) regions. There is NO reciprocal change for true anterior ischemia. [2] This setting is the cool one. If you have a proximal LAD lesion to D1 AND a wrap-around LAD, the ST changes counteract each other.
Josh