This patient with alcohol withdrawal and tachycardia had an ECG recorded:

What do you think?

There is sinus tachycardia.

Look at the QT interval: it is far more than half the QT.  The computer reads the QT at 386 ms, and QTc of 462 (proprietary correction formula unknown!)

Read this article: 

QT Correction Formulas Compared to The Rule of Thumb (“Half the QT”)

I measure the QT at 440 ms.  RR interval is 470 ms.  It is possible that what we are seeing is a fusion of the T- and U-wave, but the consequences are similar.

Here is the QTc:

Very long QT !! (Fridericia is best; at heart rates over 60, Bazett results in a QT that is too long)

The magnesium returned at 1.2 mEq/L  (low).

There was also a profound metabolic alkalosis, with K = 3.0 mEq/L.

The patient is at high risk of Torsades.

Learning Point:

Do not trust the computer measurement of the QT interval when it looks long!