Typical ECG changes in hyperkalemia begin with tall, “peaked” T waves and a shortened QT interval and progress to lengthening of the PR interval and loss of P waves. Widening of the QRS complex culminating in a “sine wave” morphology and death may occur if left untreated. (click images to enlarge)
Generally, the amplitude of the T wave goes up and down, proportional to the K+ level. The earliest ECG change seen with hypokalemia is a decrease in the T-wave amplitude. As K+ levels decline further, ST-segment depression and T-wave inversions are seen with prominent U waves.
Hypercalcemia typically causes a shortening of the ST segment and QT interval; the T wave may become widened. In severe hypercalcemia, Osborn waves (J waves) may be seen. This can progress to ventricular irritability and VF arrest if extreme hypercalcemia is left untreated.
The QT interval generally lengthens and shortens opposite to Ca2+ levels. Accordingly, hypocalcaemia causes a long ST segment and long QT interval.
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