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PATIENT 
Mr. A is a 51-year old man who arrives at the emergency department feeling weak. He has a history of a bicuspid aortic valve and aortic stenosis. One week ago, he underwent a mechanical aortic valve replacement. He denies any recent nausea, vomiting, melena, or bright red blood per rectum. He has not had a cough, dysuria, urinary frequency, abdominal pain, or fever. On physical exam his pulse is 115 bpm and BP is 85/65 mm Hg. His neck veins are visible to the angle of his jaw and his skin is cool.
At this point, what is the leading hypothesis, what are the active alternatives, and is there a must not miss diagnosis? Given this differential diagnosis, what tests should be ordered?
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RANKING THE DIFFERENTIAL DIAGNOSIS
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The first step in the evaluation is to recognize shock. Mr. A’s BP is exceptionally low for a 71-year-old man. His BP, combined with his complaint of weakness and cool extremities, makes shock likely. The next pivotal diagnostic step is to evaluate the history, physical exam, and laboratory data to determine if this is likely hypovolemic, septic, or cardiogenic shock. There are no signs or symptoms of sepsis, nor any history to suggest hypovolemia. His cool extremities are consistent with a low cardiac output state (which is often seen in hypovolemic or cardiogenic shock) and his JVD suggests that the low cardiac output is due to cardiogenic, not hypovolemic, shock. Furthermore, his past medical history increases the probability of cardiogenic shock. Possible etiologies of cardiogenic shock include poor contractility (potentially from LV or RV MI or preexistent HF), outflow obstruction (due to, for example, aortic stenosis or PE), backflow (from acute aortic regurgitation or a regurgitant aortic valve), or reduced filling (from tamponade or a stenotic mitral valve). Given the patient’s history, you consider MI to be most likely. Active alternatives include aortic valve failure or tamponade (given recent cardiac surgery). Table 25-5 lists the differential diagnosis.
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An ECG showed no evidence of MI and troponins were normal. Chest film revealed an enlarged cardiac silhouette. Measurement of pulsus ...