T-Waves

Hyperacute T-waves are often the first manifestation of complete vessel occlusion; they are wide, bulky and prominent.
Hyperacute T-waves are not necessarily tall, and small T-waves can still be hyperacute when paired with a low-amplitude QRS complex.
De Winter T-waves represent LAD occlusion (a STEMI equivalent) requiring immediate revascularization.
Previously inverted T-waves can appear normal and upright in the setting of acute vessel occlusion. This is known as pseudonormalization.
The tall T-waves associated with hyperkalemia are sharp, pointy, symmetric, and have a narrow base.
When in doubt, get serial ECGs (every 15 minutes) and use adjunctive information.