WBR0501

Author	[[PageAuthor::Gonzalo A. Romero, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pathology, MainCategory::Pathophysiology, MainCategory::Physiology
Sub Category	SubCategory::Endocrine
Prompt	[[Prompt::A 56-year-old male is treated chronically with an antiarrhythmic drug. After several months the patient comes to the clinic complaining of difficulty with concentration, constipation, decreased libido and hair loss. On physical exam the doctor notices a bluish coloration of the skin that catches the physician attention, as it is the first time seeing this unique physical sign. Which of the following changes in the cardiac cell action potential mostly correlates to the drug being used? ]]
Answer A	AnswerA::Decreases conduction velocity, increases the ERP and PR interval.
Answer A Explanation	[[AnswerAExp::Incorrect. This mechanism corresponds to calcium channel blockers.]]
Answer B	AnswerB::Decreases the AP duration, acts preferably on ischemic and depolarized ventricular tissue.
Answer B Explanation	[[AnswerBExp::Incorrect. This mechanism corresponds to class IB sodium channel blockers.]]
Answer C	AnswerC::Increases the AP duration & ERP. Increases the QT interval. Increases the Phase III.
Answer C Explanation	[[AnswerCExp::Correct. This mechanism of action corresponds to Amiodarone]]
Answer D	AnswerD::Increases AP duration, increases ERP, increases QT interval. Acts on both atria and ventricle.
Answer D Explanation	[[AnswerDExp::Incorrect. This mechanism corresponds to class IA sodium channel blockers.]]
Answer E	AnswerE::Decreases SA and AV nodal activity. Increases the PR interval. Decreases the slope of phase 4.
Answer E Explanation	[[AnswerEExp::Incorrect. This corresponds to the mechanism of action of the beta blockers.]]
Right Answer	RightAnswer::C
Explanation	[[Explanation::Overall explanation: This patient is receiving an anti-arrhythmic which is causing hypothyroidism represented by: difficulty concentrating, constipation, decreased libido and hair loss. Amiodarone typically causes thyroid problems and bluish discolorations of the skin. Educational Objective: Amiodarone causes hypothyroidism and bluish skin discoloration if used long term. References:First Aid for STEP 1 2013, endocrinology chapter Educational Objective: References: ]]
Approved	Approved::Yes
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