**Core Concept**
QT prolongation refers to an abnormal prolongation of the QT interval on an electrocardiogram (ECG), indicating delayed ventricular repolarization. This can predispose to life-threatening arrhythmias like Torsades de Pointes. Various electrolyte imbalances, medications, and cardiac conditions can cause QT prolongation.

**Why the Correct Answer is Right**
The correct answer is **tricyclic antidepressants (TCAs)**, as they are known to cause QT prolongation by blocking potassium channels, which can lead to increased action potential duration and delayed repolarization. Other options, such as **A. Hypokalemia**, **B. Hypomagnesemia**, and **D. Cisapride**, are all known to cause QT prolongation due to their effects on electrolytes and cardiac ion channels.

**Why Each Wrong Option is Incorrect**
**Option A:** Hypokalemia is a known cause of QT prolongation due to decreased potassium levels affecting cardiac repolarization.
**Option B:** Hypomagnesemia can also lead to QT prolongation by affecting potassium channel function and cardiac repolarization.
**Option D:** Cisapride, a gastroprokinetic agent, is known to cause QT prolongation due to its effects on cardiac ion channels and serotonin receptors.

**Clinical Pearl / High-Yield Fact**
It's essential to recognize that QT prolongation can be a side effect of various medications, including those used in psychiatry, cardiology, and gastroenterology. Always monitor ECGs and electrolyte levels in patients on these medications.

**Correct Answer:** A. Tricyclic antidepressants are not typically associated with QT prolongation.