WBR0795

Author	[[PageAuthor::Serge Korjian M.D. (Reviewed by Serge Korjian)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pharmacology
Sub Category	SubCategory::Cardiology
Prompt	[[Prompt::A 62-year-old man with atrial fibrillation is admitted to the hospital for cardioversion. During his hospital stay the patient suddenly develops severe dizziness and loses consciousness on his way to the bathroom. An EKG strip from the cardiac monitor is shown below. Which of the following medication could be responsible for the patient's condition? ]]
Answer A	AnswerA::Metoprolol
Answer A Explanation	AnswerAExp::Metoprolol doesn't affect the QT interval. It does not increase the risk for torsades de pointes.
Answer B	AnswerB::Lidocaine
Answer B Explanation	AnswerBExp::Lidocaine doesn't affect the QT interval. It does not increase the risk for torsades de pointes.
Answer C	AnswerC::Propafenone
Answer C Explanation	AnswerCExp::Propafenone doesn't affect the QT interval. It does not increase the risk for torsades de pointes.
Answer D	AnswerD::Dofetilide
Answer D Explanation	AnswerDExp::Dofetilide is a Class III antiarrhythmic used for cardoversion. It prolongs the QT interval and leads to torsades de pointes.
Answer E	AnswerE::Mexiletine
Answer E Explanation	AnswerEExp::Mexiletine doesn't affect the QT interval. It does not increase the risk for torsades de pointes.
Right Answer	RightAnswer::D
Explanation	[[Explanation::Torsades de pointes is a ventricular tachycardia characterized by polymorphic wave forms with typical crescendo-decrescendo pattern about the isoelectric line. Torsades de pointes is a complication of prolonged QT interval that can progress to ventricular fibrillation and sudden death. Many medications can lead to torsades de pointes, but the classical drugs associated with QT prolongation include Class IA and Class III antiarrhythmics (except amiodarone). Dofetilide is a class III antiarrhythmic used in the treatment of atrial fibrillation for the restoration of regular rhythm. It is a complication that can be seen in up to 10% of patients in certain studies often indicating the need for hospitalization and close monitoring of patients receiving this agent. Educational Objective: Torsades de pointes is a complication of medications that increase the QT interval such as Class IA and Class III antiarrhythmics namely dofetilide. References: Viskin S. Long QT syndromes and torsade de pointes. The Lancet. 1999;354(9190):1625-1633.]]
Approved	Approved::Yes
Keyword	WBRKeyword::Dofetilide, WBRKeyword::Torsades de pointes, WBRKeyword::QT prolongation, WBRKeyword::QT interval, WBRKeyword::QT, WBRKeyword::Antiarrhythmics, WBRKeyword::Class III
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