A 53-year-old woman is brought to the emergency department after she collapsed suddenly while standing and lost consciousness for approximately 3 minutes. She recovered spontaneously but was very weak and dyspneic. She also reports left-sided chest pain. There was no tonic-clonic activity or incontinence. The patient was recently diagnosed with colon cancer on a routine colonoscopy and is scheduled to undergo surgical resection. Her only other medical problem is hypertension, but she has not been compliant with her medications. Her blood pressure is 86/50 mm Hg and pulse is 120/min and regular. Pulse oximetry shows 80% on room air. She is diaphoretic and tachypneic. Jugular venous pressure is 13 cm H₂O. Lungs are clear to auscultation. Further workup in this patient would most likely show which of the following?

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11ec25c8_d4c7_e684_bc81_3740dde3ab04_MD0003_00 This patient's underlying malignancy (prothrombotic state) and acute presentation of dyspnea, chest pain, tachycardia, hypoxia, and clear lungs are highly suggestive of pulmonary embolism (PE). Patients with acute massive PE can present with syncope and hemodynamic collapse. Examination can show an accentuated (loud) pulmonic component of the second heart sound and elevated central venous pressure (eg, high jugular venous pressure [JVP]). Acute massive PE results in abrupt increases in pulmonary vascular resistance and, subsequently, right ventricular (RV) pressures. Elevated RV pressures cause increased RV wall tension, cardiac muscle stretching, and RV dilation. This increases RV myocardial oxygen demand and decreases coronary artery perfusion, which causes supply/demand mismatch and RV ischemia. Consequent RV dysfunction can lead to an inability to pump blood through the pulmonary circulation, decreased venous return to the left atrium, decreased cardiac output, and potential hemodynamic collapse. Bedside echocardiogram can show bowing of the septum into the left ventricle (due to RV pressure exceeding left ventricular diastolic pressure) and RV free-wall hypokinesis with sparing of the apex. The presence of RV dysfunction, along with elevated brain natriuretic peptide and troponin levels, is associated with increased mortality risk. (It may be difficult to differentiate PE from RV myocardial infarction [MI], which can also cause RV dysfunction; however, RVMI is less likely to cause dyspnea or syncope and more likely to cause bradycardia or arrhythmias). (Choice A) Acute mitral regurgitation can be a complication of MI and can result in cardiogenic shock. Patients will have flash pulmonary edema with crackles on examination. (Choice B) Complete heart block can cause elevated JVP and hypotension. However, bradycardia should be present. (Choice C) Acute massive PE can cause right bundle branch block on ECG. New-onset left bundle branch block suggests acute MI. Dyspnea/hypoxia in acute MI is due to pulmonary edema, which this patient does not have. (Choice D) Mediastinal widening may be seen in patients with aortic dissection. Patients typically present with sudden-onset "tearing" chest or back pain that may rapidly lead to hemodynamic collapse (due to aortic rupture or cardiac tamponade). Dyspnea and marked hypoxia are uncommon. (Choice E) Malignant pericardial effusion can result in pericardial tamponade. However, although pericardial metastasis is common in lung cancer and lymphoma, it is rare in colon cancer. In addition, tamponade can present with hypotension, but it would not cause dramatic hypoxia (as in this patient). (Choice G) Tension pneumothorax can cause hypotension and elevated JVP but will also include decreased breath sounds in that hemithorax. This is usually seen in patients on mechanical ventilation or after suffering chest trauma. Educational objective: Patients with massive pulmonary embolism usually present with signs of low arterial perfusion (eg, hypotension, syncope) and acute dyspnea, pleuritic chest pain, and tachycardia. The thrombus increases pulmonary vascular resistance and right ventricular pressure, causing right ventricular hypokinesis and dilation and hypotension. References: Right ventricular responses to massive and submassive pulmonary embolism. (http://www.ncbi.nlm.nih.gov/pubmed/22548814) Pulmonary embolism: CT signs and cardiac biomarkers for predicting right ventricular dysfunction. (http://www.ncbi.nlm.nih.gov/pubmed/21965223) Echocardiographic predictors of pulmonary embolism in patients referred for helical CT. (http://www.ncbi.nlm.nih.gov/pubmed/18652005) Right ventricular enlargement on chest computed tomography: a predictor of early death in acute pulmonary embolism. (http://www.ncbi.nlm.nih.gov/pubmed/15533868)

A 53-Year-Old Woman Is Brought to the Emergency Department After