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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}}
|QuestionAuthor= {{Rim}} (Reviewed by Serge Korjian)
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Pharmacology
|MainCategory=Pharmacology
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|MainCategory=Pharmacology
|MainCategory=Pharmacology
|SubCategory=Cardiology
|SubCategory=Cardiology
|MainCategory=Pharmacology
|MainCategory=Pharmacology
|MainCategory=Pharmacology
|MainCategory=Pharmacology
|MainCategory=Pharmacology
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|MainCategory=Pharmacology
|MainCategory=Pharmacology
|SubCategory=Cardiology
|SubCategory=Cardiology
|Prompt=A 27 year old male comes for a general check up following his last visit to Africa. He reports that he has been in Africa for three months.  He is very worried about his general health because he had severe malaria during the last visit requiring the use of an intravenous medication that caused him a lot of side effects such as headaches and tinnitus. The medication used to treat the patient also has antiarrhythmic effect.  Which of the following labeleld phased of the ventricular action potential is affected by the medication?
|Prompt=A 27-year-old man presents for his regular medical check-up following a recent visit to Cambodia. He reports severe malaria during his visit requiring intravenous treatment that led to severe headaches and tinnitus.  Which of the following phases of the ventricular action potential is affected by the medication used to treat malaria in this patient?


[[File:Ventricular action potential question.png]]
[[File:WBR1015.png]]
|Explanation=Intravenous quinidine is used for the treatment of severe complicated malaria.  Cinchonism characterized by headaches and tinnitus is a side effect of quinidine.  Quinidine is also an antiaarhythmic acting on the voltage gated sodium channels; therefore, affecting phase 0 of the ventricular action potential.
|Explanation=Intravenous quinidine is used for the treatment of severe complicated malaria.  Cinchonism characterized by headaches and tinnitus is a side effect of quinidine.  Quinidine is also an antiaarhythmic acting on the voltage gated sodium channels; therefore, affecting phase 0 of the ventricular action potential.


The ventricular action potential is composed of four phases:<br>
The ventricular action potential is composed of four phases:<br>
- Phase 0 ([[depolarization]]): abrupt opening of the voltage gated sodium channel<br>
* Phase 0 ([[depolarization]]): abrupt opening of the voltage gated sodium channel.
- Phase 1 (early repolarization): closure of the sodium channels and opening of voltage gated potassium channels<br>
* Phase 1 (early repolarization): closure of the sodium channels and opening of voltage gated potassium channels.
- Phase 2 (plateau): opening of the voltage gated calcium channels leading to an influx of calcium that balances the potassium efflux<br>
* Phase 2 (plateau): opening of the voltage gated calcium channels leading to an influx of calcium that balances the potassium efflux.
- Phase 3 (rapid repolarization): closure of the calcium channels and opening of the slow voltage gated potassium channel<br>
* Phase 3 (rapid repolarization): closure of the calcium channels and opening of the slow voltage gated potassium channel.
- Phase 4 ([[resting potential]]): high potassium permeability through the potassium channels<br>
* Phase 4 ([[resting potential]]): high potassium permeability through the potassium channels.
Shown below is an image depicting the different phases of the ventricular action potential.
Shown below is an image depicting the different phases of the ventricular action potential.


[[File:Ventricular action potential.png]]
[[File:Ventricular action potential.png]]
'''Education objective:'''
[[Quinidine]] is an antiaarhythmic acting on the voltage gated sodium channels; therefore, affecting phase 0 of the ventricular action potential.
'''Reference:'''
First aid for USMLE step 1, 2014.  Page 274, 372.
|AnswerA=A
|AnswerA=A
|AnswerAExp=A corresponds to phase 0 of the [[ventricular action potential]].  Phase 0 is characterized by a [[depolarization]] caused by the abrupt opening of the voltage gated sodium channel.  Quinidine is an antiaarhythmic acting on the voltage gated sodium channels; therefore, affecting phase 0 of the ventricular action potential.
|AnswerAExp=A corresponds to phase 0 of the ventricular action potential.  Phase 0 is characterized by a depolarization caused by the abrupt opening of the voltage gated sodium channel.  Quinidine is an antiaarhythmic acting on the voltage gated sodium channels; therefore, affecting phase 0 of the ventricular action potential.
|AnswerB=B
|AnswerB=B
|AnswerBExp=B corresponds to phase 1 of the [[ventricular action potential]].  Phase 1 is characterized by an early repolarization caused by the closure of the sodium channels and the opening of voltage gated potassium channels.  Quinidine affects phase 0 of the ventricular action potential.
|AnswerBExp=B corresponds to phase 1 of the ventricular action potential.  Phase 1 is characterized by an early repolarization caused by the closure of the sodium channels and the opening of voltage gated potassium channels.  Quinidine affects phase 0 of the ventricular action potential.
|AnswerC=C
|AnswerC=C
|AnswerCExp=C corresponds to phase 2 of the [[ventricular action potential]].  Phase 2 is characterized by a plateau.  The plateau results from the opening of the voltage gated calcium channels leading to an influx of calcium that balances the potassium efflux.  Quinidine affects phase 0 of the ventricular action potential.
|AnswerCExp=C corresponds to phase 2 of the ventricular action potential.  Phase 2 is characterized by a plateau.  The plateau results from the opening of the voltage gated calcium channels leading to an influx of calcium that balances the potassium efflux.  Quinidine affects phase 0 of the ventricular action potential.
|AnswerD=D
|AnswerD=D
|AnswerDExp=D corresponds to phase 3 of the [[ventricular action potential]].  Phase 3 is characterized by a rapid repolarization caused by the closure of the calcium channels and opening of the slow voltage gated potassium channel.  Quinidine affects phase 0 of the ventricular action potential.
|AnswerDExp=D corresponds to phase 3 of the ventricular action potential.  Phase 3 is characterized by a rapid repolarization caused by the closure of the calcium channels and opening of the slow voltage gated potassium channel.  Quinidine affects phase 0 of the ventricular action potential.
|AnswerE=E
|AnswerE=E
|AnswerEExp=E corresponds to phase 4 of the [[ventricular action potential]].  Phase 4 is characterized by a [[resting potential]] which is caused by the high potassium permeability through the potassium channels.  Quinidine affects phase 0 of the ventricular action potential.
|AnswerEExp=E corresponds to phase 4 of the ventricular action potential.  Phase 4 is characterized by a resting potential which is caused by the high potassium permeability through the potassium channels.  Quinidine affects phase 0 of the ventricular action potential.
|EducationalObjectives=Quinidine, the only intravenous therapy for the treatment of malaria, is also an antiaarhythmic that acts on the voltage gated sodium channels in the myocardium. Quinidine affects phase 0 of the ventricular action potential.
|References=Treatment of Malaria: Guidelines For Clinicians (2013). Centers for Disease Control and Prevention.<br>
First Aid 2014 page 274, 372
|RightAnswer=A
|RightAnswer=A
|WBRKeyword=Quinidine
|WBRKeyword=Quinidine, Cardiac action potential, Heart, Cardiology, Antiarrhythmic
|Approved=No
|Approved=Yes
}}
}}

Latest revision as of 02:23, 28 October 2020

 
Author [[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Serge Korjian)]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Pharmacology
Sub Category SubCategory::Cardiology
Prompt [[Prompt::A 27-year-old man presents for his regular medical check-up following a recent visit to Cambodia. He reports severe malaria during his visit requiring intravenous treatment that led to severe headaches and tinnitus. Which of the following phases of the ventricular action potential is affected by the medication used to treat malaria in this patient?

]]

Answer A AnswerA::A
Answer A Explanation [[AnswerAExp::A corresponds to phase 0 of the ventricular action potential. Phase 0 is characterized by a depolarization caused by the abrupt opening of the voltage gated sodium channel. Quinidine is an antiaarhythmic acting on the voltage gated sodium channels; therefore, affecting phase 0 of the ventricular action potential.]]
Answer B AnswerB::B
Answer B Explanation [[AnswerBExp::B corresponds to phase 1 of the ventricular action potential. Phase 1 is characterized by an early repolarization caused by the closure of the sodium channels and the opening of voltage gated potassium channels. Quinidine affects phase 0 of the ventricular action potential.]]
Answer C AnswerC::C
Answer C Explanation [[AnswerCExp::C corresponds to phase 2 of the ventricular action potential. Phase 2 is characterized by a plateau. The plateau results from the opening of the voltage gated calcium channels leading to an influx of calcium that balances the potassium efflux. Quinidine affects phase 0 of the ventricular action potential.]]
Answer D AnswerD::D
Answer D Explanation [[AnswerDExp::D corresponds to phase 3 of the ventricular action potential. Phase 3 is characterized by a rapid repolarization caused by the closure of the calcium channels and opening of the slow voltage gated potassium channel. Quinidine affects phase 0 of the ventricular action potential.]]
Answer E AnswerE::E
Answer E Explanation [[AnswerEExp::E corresponds to phase 4 of the ventricular action potential. Phase 4 is characterized by a resting potential which is caused by the high potassium permeability through the potassium channels. Quinidine affects phase 0 of the ventricular action potential.]]
Right Answer RightAnswer::A
Explanation [[Explanation::Intravenous quinidine is used for the treatment of severe complicated malaria. Cinchonism characterized by headaches and tinnitus is a side effect of quinidine. Quinidine is also an antiaarhythmic acting on the voltage gated sodium channels; therefore, affecting phase 0 of the ventricular action potential.

The ventricular action potential is composed of four phases:

  • Phase 0 (depolarization): abrupt opening of the voltage gated sodium channel.
  • Phase 1 (early repolarization): closure of the sodium channels and opening of voltage gated potassium channels.
  • Phase 2 (plateau): opening of the voltage gated calcium channels leading to an influx of calcium that balances the potassium efflux.
  • Phase 3 (rapid repolarization): closure of the calcium channels and opening of the slow voltage gated potassium channel.
  • Phase 4 (resting potential): high potassium permeability through the potassium channels.

Shown below is an image depicting the different phases of the ventricular action potential.


Educational Objective: Quinidine, the only intravenous therapy for the treatment of malaria, is also an antiaarhythmic that acts on the voltage gated sodium channels in the myocardium. Quinidine affects phase 0 of the ventricular action potential.
References: Treatment of Malaria: Guidelines For Clinicians (2013). Centers for Disease Control and Prevention.
First Aid 2014 page 274, 372]]

Approved Approved::Yes
Keyword WBRKeyword::Quinidine, WBRKeyword::Cardiac action potential, WBRKeyword::Heart, WBRKeyword::Cardiology, WBRKeyword::Antiarrhythmic
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