Hypercalcemia, high blood calcium, speeds repolarization. Characteristics of hypercalcemia:
- Mild: broad based tall peaking T waves
- Severe: extremely wide QRS, low R wave, disappearance of p waves, tall peaking T waves.
ECG-characteristics of hypocalcemia, low blood calcium:
- Narrowing of the QRS complex
- Reduced PR interval
- T wave flattening and inversion
- Prolongation of the QT-interval
- Prominent U-wave
- Prolonged ST and ST-depression
ECG characteristics of hyperkalemia, high blood potassium:
- Tall peaked T waves
- Flattening p-waves. In extreme hyperkalemia p-waves may disappear altogether.
- Prolonged depolarization leading to QRS widening (nonspecific intraventricular conduction defect) sometimes > 0.20 seconds
At concentrations > 7.5 mmol/L atrial and ventricular fibrillation can occur.