ECG

Hyperkalemia

• narrowing and peaking of T waves
• AV conduction  delay
• diminution of P waves
• prolonged PR interval and widening of QRS interval
• sine-wave pattern

Hypokalemia

• flattening or inversion of T waves
• prominent U waves
• ST segment depression
• prolonged QU  interval
• severe hypokalemia-prolonged PR interval, decreased voltage and widening of QRS complex

Hypermagnesemia

• changes similar to those of hyperkalemia

Hypomagnesemia

• changes similar to those of hypokalemia

Hypercalcemia

• shortening of QT interval

Hypocalcemia

• prolongation of QT interval

Uraemia

• changes similar to those of hypocalcemia in association with hyperkalemia

Hypothermia

• prolongs repolarization, usually with a distinct convex elevation of the J point ( Osborn Wave)

Pericarditis

• in acute phase , there is ST segment elevation with convexity upwards diffusely in all leads except aVR and there is no reciprocal ST depression.

Digitalis effect

• the T wave is flattened at therapeutic levels and there is no reciprocal ST depression

SAH

• marked QT prolongations with deep , wide T wave inversions  ( CVA-T wave pattern)

WPW syndrome

• wide QRS , short PR interval and slurring of the initial part of the QRS (delta wave) 

Pulmonary thromboembolism

• sinus tachycardia ( most common manifestation) , S wave in lead I , a Q wave in lead III and an inverted T wave in lead III ( S1 Q 3 T3)