WBR1014

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Author [[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Physiology
Sub Category SubCategory::Cardiology
Prompt [[Prompt::A 75 year old female patient complains of dyspnea and generalized fatigue. She is short of breath mainly when she is lying down. The shortness of breath is very severe at night when she sleeps or when she climbs the stairs. Laboratory tests and echocardiography of the heart are ordered. Echocardiography reveals abnormal filling dynamics of the left ventricle with preserved contractility which is associated with elevated left atrial filling pressures and left atrial enlargement. Which of the following most likely corresponds to the end-disatolic and end-systolic volumes measured in the left ventricle of this patient?]]
Answer A AnswerA::200 and 60 mL
Answer A Explanation [[AnswerAExp::The ejection fraction calculated from the given end-systolic and end-diastolic volume is 70%. An ejection fraction of 70% is considered normal. Diastolic heart failure is characterized by a normal ejection fraction.]]
Answer B AnswerB::200 and 100 mL
Answer B Explanation [[AnswerBExp::The ejection fraction calculated from the given end-systolic and end-diastolic volume is 50%. An ejection fraction of 50% is considered low.]]
Answer C AnswerC::180 and 100 mL
Answer C Explanation [[AnswerCExp::The ejection fraction calculated from the given end-systolic and end-diastolic volume is 44%. An ejection fraction of 44% is considered low.]]
Answer D AnswerD::150 and 75 mL
Answer D Explanation [[AnswerDExp::The ejection fraction calculated from the given end-systolic and end-diastolic volume is 50%. An ejection fraction of 50% is considered low.]]
Answer E AnswerE::110 and 70 mL
Answer E Explanation [[AnswerEExp::The ejection fraction calculated from the given end-systolic and end-diastolic volume is 36%. An ejection fraction of 36% is considered low.]]
Right Answer RightAnswer::A
Explanation [[Explanation::This patients presents with symptoms of heart failure with echocardiographic findings suggestive of diastolic heart failure. Diastolic heart failure is characterized by abnormal relaxation and/or filling of the ventricles. It can be associated with left atrial enlargement due to the elevated pressures in the left heart.

The ejection fraction differentiates systolic heart failure from diastolic heart failure which are two entities with different underlying pathophysiology. Systolic heart failure is characterized by a decreased ejection fraction, while diastolic heart failure is characterized by a normal ejection fraction.
The ejection fraction can be calculated as follows:
Ejection fraction= (end-diastolic volume -end-systolic volume)/ end-diastolic volume
A normal ejection fraction ranges from 55 to 75%. Answer A corresponds to an ejection fraction of 70% which is within the normal range.

Educational objective:
Diastolic heart failure is characterized by a normal ejection fraction. The ejection fraction can be calculated as follows:
Ejection fraction= (end-diastolic volume -end-systolic volume)/ end-diastolic volume

Reference: First aid for USMLE step 1, 2014. Page 267.
Educational Objective:
References: ]]

Approved Approved::No
Keyword WBRKeyword::Ejection fraction, WBRKeyword::diastolic heart failure
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