Further clarification on case study

One of our readers the (author of insane student) commented to our case study post:

Correct me if i am wrong, but i can see st elevations most prominent on leads II,III and aVF. isn't that an inferior MI and in this case the Right coronary artery should be obstructed? on the other hand, the st segments on the chest leads are not significantly elevated as to be consistent with a total occlusion of the LAD. Could you pl explain?

So here's the reply for Ms Adeline:

What you are asking is whether the surface 12 lead ECG is a good predictor of vessel occlusion/disease. The short and simple answer is no.

A longer answer is that the surface ECG is a reasonable guide to vessel occlusion/disease. Please understand that although we talk about the RCA.LCA-LAD/LcX, these are arteries going to territories of supply. When the inferior surface is ischemic/infarcted, it could be the result of the RCA occlusion (as you have said) if the RCA is large and the LAD/LCx smallish, or a small RCA and a large LAD which wraps around the apex of the heart to supply the inferior surface via a large PDA branch. Think territory (and myocardium at risk), which roughly corelates with arteries.