This patient presented after dialysis with weakness and reproducible chest pain.

Sinus rhythm with a normal QRS.  The QT is prolonged and this is due to a long ST segment.  There are prominent U-waves, best seen in II, V2, and V3.

This patient presented in shock with GI bleeding, cirrhosis, and a lactate of 33.

There is widespread scooped ST depression, a very long QT, a long ST segment, and prominent U-waves which are easily mistaken for T-waves (as if the T-wave were biphasic down then up).  The terminal portion of what appears to be a down up T-wave is really a U-wave, best seen in V4 and aVF.

These are both cases of simultaneous hypokalemia (U-waves and ST depression) and hypocalcemia.  In the first case, the K was 3.1 and Ca was 3.8 ionized.  In the second case, the K was 2.9 and Ca 6.3 nonionized.  Hypokalemia gives a prolonged QT, scooped ST depression, prominent U-waves, and often a generally wavy appearance to the ECG.  Hypocalcemia gives a long ST segment resulting in a long QT.

In the second case, troponin I was negative.  ST depression was not due to NSTEMI.  ST depression with a normal QRS (“primary”) is due to ischemia, hypokalemia, digoxin, and an abnormal baseline (unknown etiology).  Of course there is also “secondary” ST depression, secondary to an abnormal QRS such as LVH, BBB, Brugada, WPW, etc.