antipsychotic which causes torsades de pointes
I remember that certain antipsychotics, especially some of the older ones like thioridazine and pimozide, are notorious for causing QT prolongation. More recently, quetiapine (Seroquel) has also been linked to this effect, though it's a second-generation antipsychotic. Olanzapine and risperidone are less likely to cause torsades.
Wait, the question didn't list the options. The user left them as A to D without labels. But since the correct answer is supposed to be one of them, I need to assume possible options. Let's say the options are typical antipsychotics. For example, A could be haloperidol, B might be clozapine, C could be risperidone, and D could be quetiapine. Alternatively, maybe pimozide is an option. Since the correct answer here is quetiapine, I need to structure the explanation around that.
The core concept here is the mechanism of QT prolongation by certain antipsychotics. The Core Concept should mention that these drugs block potassium channels, leading to prolonged repolarization. The correct answer explanation would detail how quetiapine inhibits the hERG potassium channel, which is crucial for the rapid component of the cardiac repolarization phase.
Then, for the incorrect options: haloperidol can cause QT prolongation but is more associated with extrapyramidal side effects. Clozapine is known for agranulocytosis. Risperidone has a lower risk compared to others. Pimozide is another one that causes torsades, but maybe it's not the most common answer here. The clinical pearl would be to remember that quetiapine has a black box warning for torsades, especially at higher doses. Also, checking the QT interval in patients on these meds is important.
I need to make sure the explanation is concise, covers all sections, and fits within the character limit. Let me structure each part step by step, keeping it clear and precise for a medical student preparing for exams like NEET or USMLE.
**Core Concept**
Torsades de pointes is a polymorphic ventricular tachycardia caused by **QT interval prolongation**, often due to **blockade of the hERG potassium channel (IKr)** in cardiac myocytes. Antipsychotics with high affinity for this channel are associated with this arrhythmia.
**Why the Correct Answer is Right**
**Quetiapine** (Seroquel) is a second-generation antipsychotic that inhibits **hERG potassium channels**, delaying myocardial repolarization and inducing **QT prolongation**. This increases the risk of **torsades de pointes**, especially in patients with electrolyte imbalances (e.g., hypokalemia, hypomagnesemia) or concomitant use of other QT-prolonging drugs.