WBR1103

Author	PageAuthor::William J Gibson
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Behavioral Science/Psychiatry, MainCategory::Pharmacology
Sub Category	SubCategory::Cardiology
Prompt	[[Prompt::A 38-year-old schizophrenic male is found unconscious and pulseless by healthcare workers at his assisted living facility. Emergency personnel were able to revive the patient by defibrillation and the patient was admitted to the hospital. He was monitored by 24-hour-telemetry, a portion of which is shown below. The patient has no prior history of cardiac disease. Which of the following medications is most likely responsible for this patient's loss of consciousness?]]
Answer A	AnswerA::Lithium
Answer A Explanation	[[AnswerAExp::Lithium is a mood-stabilizer used for treating bipolar disorder. Lithium toxicity includes movement disorder (Extrapyramidal symptoms), nephrogenic diabetes insipidus, hypothyroidism, and teratogenicity. Prolonged QT-interval is not considered a feature of lithium toxicity.]]
Answer B	AnswerB::Chloropromazine
Answer B Explanation	[[AnswerBExp::Chlorpromazine is a typical antipsychotic that can be used to treat schizophrenia. Toxicity of chlorpromazine and other typical antipsychotics includes extrapyramidal side effects (dyskinesias), as well as endocrine side effects such as hyperprolactinemia.]]
Answer C	AnswerC::Thioridazine
Answer C Explanation	AnswerCExp::Thioridazine is a typical antipsychotic that is thought to function by antagonizing the dopamine D2 receptor. Thioridazine potently prolongs the QT interval and has been documented to cause Torsades de Pointes.
Answer D	AnswerD::Hydrochlorothiazide
Answer D Explanation	AnswerDExp::While hydrochlorothiazide can cause prolonged QT interval, we have no reason to believe that this patient is on hydrochlorothiazide. Because of this patient’s history of schizophrenia, risperidone is a more appropriate choice.
Answer E	AnswerE::Haloperidol
Answer E Explanation	[[AnswerEExp::Haloperidol is a high potency typical antipsychotic whose mechanism of action involves blocking dopamine D2 receptors. Haloperidol toxicity is typically manifested as extrapyramidal side effects, including tardive dyskinesia. Haloperidol is not associated with QT interval prolongation.]]
Right Answer	RightAnswer::C
Explanation	[[Explanation::Thioridazine is a typical antipsychotic that prolongs the QTc interval in a dose-dependent manner. It was previously widely used in the treatment of schizophrenia but was largely discontinued due to cardiotoxicity and retinopathy. The electrocardiogram from this patient demonstrates a widened QT interval. The QT interval represents electrical depolarization and repolarization of the ventricles. A lengthened QT interval is a marker for the potential of ventricular tachyarrhythmias like torsades de pointes and a risk factor for sudden death. Note: While First Aid 2014 claims that risperidone lengthens the QT interval and may cause Torsades de Pointes, there is no evidence that risperidone increases the risk of Torsades de Pointes (see review by Glassman et al.). Educational Objective: Thioridazine potently prolongs the QT interval and has been documented to cause Torsades de Pointes. References: Glassman AH, Bigger JT. Antipsychotic drugs: prolonged QTc interval, torsade de pointes, and sudden death. Am J Psychiatry. 2001;158(11):1774-82. First Aid 2015 page 283 (Long QT and Torsades de pointes) First Aid 2015 page 521 (Antipsychotics) First Aid 2014 page 277 (Long QT and Torsades de pointes) First Aid 2014 page 517 (Antipsychotics) ]]
Approved	Approved::Yes
Keyword	WBRKeyword::Arrhythmia, WBRKeyword::EKG, WBRKeyword::ECG, WBRKeyword::Torsades de pointes, WBRKeyword::QT interval, WBRKeyword::antipsychotic, WBRKeyword::Schizophrenia, WBRKeyword::Cardiology, WBRKeyword::Side effect, WBRKeyword::Cardiac electrophysiology
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