Final answer:
QTc prolongation can result from electrolyte imbalances, particularly lowered calcium levels, and the use of calcium channel blockers, which reduce calcium ion flow into the heart cells.
Step-by-step explanation:
QTc prolongation can be caused by an imbalance in electrolytes, particularly calcium. The QT interval on an electrocardiogram (ECG) represents the period from the start of ventricular depolarization to repolarization. If calcium ion levels drop, this can cause a prolonged QTc. However, high levels of calcium ions (hypercalcemia) are more likely to cause a short QT interval. Conversely, drugs like calcium channel blockers may prolong the QT interval by reducing the inward movement of calcium ions, which slows heart rate (HR) and decreases myocardial contractility.
It is important to note that there are other factors that can cause QT prolongation, such as certain medications, genetic conditions, and other electrolyte disturbances beyond calcium, including potassium and magnesium levels.