This 64 year old woman presented intoxicated with nausea and vomiting and epigastric pain, with no chest pain. She has a history of a stent, but unknown in which artery. She stopped taking clopidogrel 2 weeks ago because she ran out. Here is the initial ECG; there was no previous ECG for comparison.
Notice there is deep symmetric T inversions in inferior leads, and a large upright T wave in aVL. There is also some T inversion laterally. This is all suggestive of inferior (and lateral?) Non-STEMI, due to reperfused RCA or circ. Inverted T waves are also known as "reperfusion" T-waves. If they are in the anterior leads, they are often referred to as "Wellens' T-waves."
A troponin returned elevated, and a repeat ECG was recorded:
Now the inferior T-waves have become mostly upright, in this case biphasic. There is some ST elevation, but it is not quite 1 mm in two consecutive leads. There is new ST elevation in lead V1, which in this context is diagnostic of right ventricular STEMI.
This phenomenon is called "pseudonormalization of T-waves" because normal T-waves are upright (same axis as QRS), but become inverted in non-STEMI that is reperfused. They become deceptively upright (not normal, but "pseudo" normal) when the artery re-occludes. Thus, where reperfusion of the infarct-related artery (IRA) leads to T-wave inversion, if inverted leads become suddenly upright, this is diagnostic of re-occlusion of the IRA.
There is nothing magical about 1 mm of ST elevation. ST elevation is used as a very imperfect surrogate for coronary occlusion. Coronary occlusion that does not spontaneously reperfuse or is not compensated for by collateral circulation will quickly lead to irreversible myocardial loss. Reperfusion therapy is indicated for occlusion, even when there is not 1 mm of STE in 2 consecutive leads. However, the specificity of the ECG for occlusion becomes less as the STE is less. So expertise in interpreting the ECG is particularly important for these cases.
In this case, it was clear that there was a very unstable thrombus in the RCA or circ, and that if it was not 100% occlusive, it was very nearly so.
The cath lab was activated, a 100% proximal RCA stent thrombosis was seen and the artery was opened.
This also illustrates how chest pain or even discomfort may be completely absent in STEMI. Below is the post-cath ECG, showing T-waves are now inverted again (indicating reperfusion).