T Wave Inversion

T wave abnormalities are much less specific overall compared to ST segment abnormalities for diagnosing myocardial ischemia. Similar to ST segment changes, they may be dynamic changes overall. T wave inversions are considered to be evidence of myocardial infusion if they are at least 1mm deep, present in at least 2 contiguous leads with a dominant R wave (R/S ratio>1), and dynamic. The last criteria can be the most difficult to appreciate and requires either prior EKG's to be available or good clinical correlation, usually. It is also important to remember the 'normal variants' with T wave inversions; leads III, aVR, and V1 commonly have T wave inversions that are not representative of pathology. It is also important to remember that T wave inversion may be the first reciprocal change in a OMI (and is often the first EKG change in an inferior OMI). Note that T wave inversions may localize, unlike ST depressions from myocardial ischemia. Fixed T wave inversions are typically from prior ischemia if they are not from non-ischemic etiologies. T wave inversions that are symmetric are more likely to be from ischemia compared to asymmetric T wave inversions.

T wave flattening or T wave inversion <1mm is much less specific and may be indicative of myocardial ischemia, though not diagnostic ('nonspecific changes'). It is very common to see T wave changes that are secondary to other pathology (ie bundle branch block, electrolyte abnormalities). Generalized T wave inversions are more commonly from secondary causes (usually electrolyte abnormalities).  T wave inversions secondary to ICH are usually extremely large and bizarre and should not be confused with ischemic T waves. T waves with a down-up appearance (partial inversion) are overall much more specific for ischemia as well, though should be differentiated from the scooping ST segment, inverted T wave, and upright U wave of hypokalemia.

Examples:

Further Reading:

https://litfl.com/myocardial-ischaemia-ecg-library/

https://litfl.com/t-wave-ecg-library/

http://hqmeded-ecg.blogspot.com/search/label/T-Wave%20inversion

http://hqmeded-ecg.blogspot.com/search/label/Up-Down%20T-waves