Effects of hyperkalemia on the ECG:

K > 5.5 mEq/L
Peaked T waves (usually the earliest sign of hyperkalaemia)

K > 6.5 mEq/L
P wave widens and flattens
PR segment lengthens
P waves eventually disappear

K > 7.0 mEq/L
Wide QRS complexes with bizarre QRS morphology
ST elevation
High-grade AV block
Any kind of conduction block (bundle branch blocks, fascicular blocks)
Sinus bradycardia or slow AF
Development of a sine wave appearance

K > 9.0 mEq/L
Asystole
Ventricular fibrillation
PEA with bizarre, wide complex rhythm