Torsade de pointes is caused by
**Core Concept**
Torsade de pointes is a specific type of polymorphic ventricular tachycardia characterized by a rapid, irregular heart rhythm that can degenerate into ventricular fibrillation, leading to cardiac arrest. This arrhythmia is often associated with a prolonged QT interval on the electrocardiogram (ECG).
**Why the Correct Answer is Right**
Torsade de pointes is typically caused by a prolongation of the QT interval, which can be due to a variety of factors such as congenital long QT syndrome, acquired conditions like hypokalemia or hypomagnesemia, or the use of certain medications like quinidine, sotalol, or cisapride. The prolonged QT interval allows for the formation of abnormal electrical pathways in the heart, leading to the characteristic twisting or "de pointes" pattern on the ECG. The mechanism involves the accumulation of late sodium current (I_Na) and the resulting prolongation of the action potential duration in the ventricular myocytes.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided.
**Option B:** While bradycardia can contribute to the development of torsade de pointes, it is not a direct cause of the arrhythmia.
**Option C:** While ischemia can cause various arrhythmias, it is not a primary cause of torsade de pointes.
**Clinical Pearl / High-Yield Fact**
A key risk factor for torsade de pointes is the use of medications that prolong the QT interval. It is essential for clinicians to carefully evaluate the ECG and medication list of patients at risk for this arrhythmia.
**Correct Answer:** D. The use of certain medications like quinidine, sotalol, or cisapride.