WBR0428

Author	[[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D. and Alison Leibowitz [1])]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pathology
Sub Category	SubCategory::Cardiology
Prompt	[[Prompt::A 57-year-old man is brought to the emergency department with acute-onset, severe chest pain. The patient's wife reports he had a upper respiratory infection 6 days ago. In the ED, his temperature is 37.0 °C (98.6 °F), heart rate is 112/min, and blood pressure is 80/50 mmHg. Physical examination is remarkable for jugular venous distension (JVD) and weakness of the peripheral radial pulse upon inspiration. What is the most important determinant of severity of the clinical presentation of this patient’s condition?]]
Answer A	AnswerA::Rate of fluid accumulation relative to pericardial stretch
Answer A Explanation	AnswerAExp::The rate of fluid accumulation relative to pericardial compensatory stretch mechanisms plays a significant role in the clinical presentation of cardiac tamponade.
Answer B	AnswerB::Plaque rupture and location of thrombus formation within the coronary artery
Answer B Explanation	[[AnswerBExp::A plaque rupture and the location of thrombus formation play an important role in the clinical presentation among patients who present with a myocardial infarction (MI).]]
Answer C	AnswerC::Patient’s past medical history
Answer C Explanation	AnswerCExp::The patient's pericarditis is caused by the patient's recent upper respiratory infection. However, the patient's past medical history is not associated with the severity of his presentation.
Answer D	AnswerD::Amount of fluid accumulation within the pericardial sac
Answer D Explanation	AnswerDExp::Although the amount of fluid accumulation is important, even larger volumes of accumulated fluid may be associated with no symptoms had the fluid accumulated over a prolonged period of time.
Answer E	AnswerE::Weakness of peripheral radial pulse upon inspiration
Answer E Explanation	[[AnswerEExp::Pulsus paradoxus is defined as a fall in systolic blood pressure > 10 mmHg upon normal breathing. It is a clinical feature of cardiac tamponade but it is not a specific sign on physical examination. It may also be present in other cardiac diseases (cardiogenic shock), pulmonary diseases (COPD, asthma, interstitial lung disease, obstructive sleep apnea, pulmonary hypertension, PE), and non-cardiac non-pulmonary diseases (e.g. superior vena cava obstruction). Pulsus paradoxus occurs when arterial pressure falls significantly with inspiration due to increased right ventricular filling with decreased left ventricular filling.]]
Right Answer	RightAnswer::A
Explanation	[[Explanation::Cardiac tamponade is a potentially is characterized by a decrease in cardiac output due to pericardial accumulation (fluid, blood, pus, clots, or gas) that compresses the cardiac chambers. Cardiac tamponade may be a complication of a ruptured myocardial infarction, a recent cardiothoracic procedure, tuberculous infection, neoplasia, uremia, or pericarditis. The primary abnormality of cardiac tamponade is the compression of the heart chambers that results in an elevated intrapericardial pressure. As the pericardial fluid expands, the pericardium stretches to accomodate the gradually increasing volume. As the amount of fluid further increases, however, the pericardium then becomes inextensible, and the heart chambers are then affected by the increasing pericardial pressure. The heart chambers will progressively become smaller and mean diastolic pericardial and chamber pressures will ultimately equalize. The most important determinant of the severity of clinical presentation of cardiac tamponade is the rate of fluid accumulation. In the case of slow and chronic fluid accumulation, compensatory cardiac stretch mechanisms are adequate, and patients may remain asymptomatic for a prolonged period of time. In contrast, clinical presentations are much more severe when fluid accumulates rapidly and cardiac stretch mechanisms are not granted sufficient time for compensation. Cardiac tamponade is a subtype of cardiogenic shock. The majority of patients present in a confused state and may have no symptoms. Symptoms are usually non-specific and include dyspnea with, chest pain/discomfort, dysphagia, or cough. Vital signs classically demonstrate tachypnea, tachycardia, and hypotension. Physical examination may be remarkable for faint heart sounds (sounds blocked by accumulated fluid), jugular venous distention or pulsations without distention, Kaussmaul sign (increase in JVP upon inspiration), pulsus paradoxus (fall in systolic blood pressure > 10 mmHg upon normal breathing), and cool extremities. Beck's triad of cardiac tamponade refers to the triad of faint heart sounds, hypotension, and jugular venous distention. ECG findings classically include electrical alternans in all waves or only the QRS (alternations of large and small waves), but the majority of patients have signs of pericarditis on ECG (low voltage in all leads, ST-elevations in all leads, PR-segment depression). Doppler echocardiography is an important diagnostic tool and shows pericardial effusion with swinging of the heart, compressed cardiac chambers, and collapsed chambers. First step in management is drainage of the compressing pericardial fluid. Educational Objective: Cardiac tamponade is the compression of the heart chambers by pericardial fluid. The rate of fluid accumulation and the compensatory cardiac mechanisms determine the clinical manifestations of cardiac tamponade. References: Spodick D. Acute Cardiac Tamponade. N Eng J Med. 2003;349:684-690. First Aid 2014 page 293]]
Approved	Approved::Yes
Keyword	WBRKeyword::Cardiac tamponade, WBRKeyword::Pulsus paradoxus, WBRKeyword::Hypotension, WBRKeyword::Jugular venous distention, WBRKeyword::Beck triad, WBRKeyword::Pericardial effusion
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