What effect does hypercalcaemia have on the QT interval?

Hypercalcaemia, which is defined as an elevated level of calcium in the blood, has a well-established physiological impact on cardiac function, particularly concerning the QT interval on an electrocardiogram (ECG). Elevated calcium levels are associated with a reduction in the duration of the QT interval.

This occurs because calcium plays a vital role in cardiac action potentials. An increase in extracellular calcium concentration enhances the influx of calcium during the plateau phase of the action potential, which in turn accelerates the repolarization phase. This leads to a shortening of both the QT interval and the overall duration of the action potential.

In contrast, other electrolyte abnormalities, such as hypocalcaemia (low calcium levels), tend to lengthen the QT interval. Each electrolyte can influence cardiac electrical activity, and their effects are often predictable based on their physiological roles.

Contextually, while it could be argued that certain conditions may have variable effects on the QT interval, in the case of hypercalcaemia, the direct physiological effects consistently lead to a shortening of the QT interval, making this the correct interpretation.