WBR0839

Author	PageAuthor::Neeraja Danda M.B.B.S
Exam Type	ExamType::USMLE Step 2 CK
Main Category	MainCategory::Internal medicine
Sub Category	SubCategory::Cardiovascular
Prompt	[[Prompt::A 38 Year old male crashed his car in to a tree while speeding. Vitals are Pulse rate 115/min, Blood pressure 100/70 and become 78/58 on inhalation and respiratory rate 28/min. On physical examination neck veins are distended. Electrocardiogram shows QRS complexes of varying heights. Such presentation on Electrocardiogram is characteristic of which of the following?]]
Answer A	AnswerA::Constrictive pericarditis
Answer A Explanation	AnswerAExp::'''Incorrect''' Electrocardiogram in pericarditis is characterized by ST segment elevation in all the leads.
Answer B	AnswerB::Pericardial tamponade
Answer B Explanation	AnswerBExp::Electical alternans is defined by an electrocardiogram with QRS complexes of varying heights, a common feature of pericardial tamponade.
Answer C	AnswerC::Pneumothorax
Answer C Explanation	[[AnswerCExp::Incorrect Pneumothorax is presence of air in the pleural space. It is characterized by decreased breath sounds on the affected side. Electrical alternans is not seen in this condition. However suspicion for pneumothorax following a stab wound to the chest should be high.]]
Answer D	AnswerD::Ischemic heart disease
Answer D Explanation	AnswerDExp::'''Incorrect''' In ischemic heart disease, the electrocardiogram shows ST elevation or depression. The location of ST segment changes in particular leads can help determine the infracted portion of the heart.
Answer E	AnswerE::Heart failure
Answer E Explanation	AnswerEExp::'''Incorrect''' Heart failure is not characterized by electrical alternans.
Right Answer	RightAnswer::B
Explanation	[[Explanation::The patient in this vignette is suffering from pericardial tamponade. Electical alternans is defined by an electrocardiogram with QRS complexes of varying heights, a common feature of pericardial tamponade. Tachycardia, hypotension, pulsus paradoxus and jugular venous distension in this case are also characteristic of pericardial tamponade. In this case, a stab wound has caused ventricular rupture and rapid collection of blood in the pericardium. As little as 100mL of fluid can cause tamponade in the case of rapid accumulation, such as trauma or ventricular rupture. Pulsus paradoxus is a drop in the blood pressure more than 10 mm of hg on inspiration. Pericardial tamponade is also referred to as cardiac tamponade. Educational Objective: Electrical alternans is characterized by varying heights of QRS complexes on electrocardiogram and is a characteristic finding in pericardial tamponade. References: page 64, 99,100, 384 Master the boards step 2 CK second edition, Page 69 Master the boards Step 3 2009 Educational Objective: References: ]]
Approved	Approved::Yes
Keyword	WBRKeyword::Elactrical Alternans, WBRKeyword::Pericardial Tamponade
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Order in Linked Questions	LinkedOrder::