Hypercalcemia may cause electrocardiogram changes, predominantly in the duration of the ST segment and the QT interval, due to alterations in the duration of the phase 2 of the action potential
These are the features of hypercalcemia on ECG;
1. Shortening of the QT interval (primarily due to a decrease in phase 2 of the ventricular action potential and resultant decrease in the ST segment duration)
2. Decrease in duration of the upstroke of the T wave (fig 2) ( the initial portion of the T wave has an abrupt upslope).
3. PR prolongation,
4. An increase in the amplitude of the QRS complex,
5. Flattened, inverted, or biphasic T waves.