Electrical alternans is an electrocardiographic phenomenon which describes the beat to beat alternation in the height (ie. amplitude), duration (the length of the<unk>  or the direction (up or down) of any of the EKG complexes or<unk> s.  While electrical alernans is usually thought of as alternation in the height or direction of the QRS complex, there can also be P wave,<unk><unk> , QRS complex, R-R<unk> , ST segment, T wave, or U wave forms of alternans (see classification below).
PR interval alternans
U wave alternans
T wave alternans
Sine wave pattern
Low QRS voltage
Tombstone ST elevation
Inverted P wave
T wave inversion