What effect do potassium and calcium imbalances have on which ECG feature?

The effect of potassium and calcium imbalances on the ECG is primarily reflected in the T wave. In particular, alterations in potassium levels can lead to significant changes in T wave morphology. For instance, hyperkalemia typically causes tall, peaked T waves, while hypokalemia can lead to flattened or inverted T waves.

Calcium imbalances also influence the T wave, but they primarily affect the action potential duration and could cause a prolonged T wave or changes associated with QT interval prolongation. Therefore, both potassium and calcium levels are critical in determining the characteristics of the T wave on the ECG, which is why it is the most relevant feature when considering the effects of these electrolyte imbalances.