WBR1016
| Author | [[PageAuthor::Rim Halaby, M.D. [1]]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Pharmacology |
| Sub Category | SubCategory::Cardiology |
| Prompt | [[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?
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| 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:
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. |
| Approved | Approved::No |
| Keyword | WBRKeyword::Quinidine |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |
