Which condition may cause a prolonged QT interval?

A prolonged QT interval on an electrocardiogram (ECG) can indicate disturbances in the heart's electrical activity, which can be a critical condition to monitor. Hypocalcemia, or low levels of calcium in the blood, is indeed known to affect the cardiac action potential. Calcium plays a pivotal role in cardiac myocyte function, particularly during the plateau phase of the action potential. When calcium levels are low, it can lead to a delay in repolarization, which extends the QT interval.

This prolongation occurs because calcium affects the conductance and timing of the cardiac action potentials, specifically during the phase of repolarization. An extended QT interval can increase the risk of serious arrhythmias, such as Torsades de Pointes, a potentially life-threatening condition.

The other conditions listed do not directly contribute to a prolonged QT interval in the same way. Hyperkalemia can alter the QT interval but usually shortens it. Atrial flutter primarily affects the atrial rate and rhythm rather than the ventricular repolarization time. Myocardial infarction can lead to various changes in the ST segment and T waves but is not specifically associated with consistent QT interval prolongation as is hypocalcemia. Thus, hypocalcemia stands out