A 53-year-old man comes to the physician complaining of worsening weakness and exertional dyspnea over the past 2 days. He had an upper respiratory illness 3 weeks ago but the symptoms never resolved completely. He has no chest pain or palpitations. His father died of a myocardial infarction at age 55. His blood pressure is 87/60 mm Hg and pulse is 109/min. Oxygen saturation is 95% on room air. His body mass index is 23 kg/m². Internal jugular venous pulsation is 11 cm H₂O. Lungs are clear to auscultation. Heart sounds are muffled. Which of the following is the most likely cause of this patient's complaints?

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This patient's presentation suggests pericardial effusion and cardiac tamponade. The etiology is most likely infectious (viral pericarditis) due to his recent upper respiratory viral illness. This patient has all 3 features of Beck's triad associated with cardiac tamponade: hypotension, distended neck veins, and muffled heart sounds. Pulsus paradoxus (>10 mm Hg drop in systolic blood pressure during inspiration) is also a common finding. Abdominal examination can also show positive hepatojugular reflux. Cardiac tamponade is due to fluid accumulation in the pericardial cavity that increases the intrapericardial pressure above the diastolic ventricular pressure. This restricts venous return to the heart and lowers right and left ventricular filling. The net result is decreased preload, stroke volume, and cardiac output. Lung examination typically shows clear lungs to auscultation due to decreased ventricular filling (preload) rather than volume overload. Inspiration worsens this condition by lowering the intrathoracic pressure and increasing venous return to the right ventricle. Under normal conditions, the right ventricle is able to accommodate this increased venous return by expanding the right ventricular free wall. Cardiac tamponade decreases right ventricular compliance and shifts the interventricular septum toward the left ventricular cavity to further reduce left ventricular filling (Choice C). This mechanism is also responsible for pulsus paradoxus (>10 mm Hg drop in systolic pressure during inspiration) in patients with cardiac tamponade. (Choice A) Decreased cardiac contractility is observed in patients with systolic heart failure. They typically have signs of both left ventricular failure (eg, crackles on pulmonary examination and an S3) and right ventricular failure (eg, jugular venous distension and peripheral edema). Cardiac contractility and heart rate are increased in cardiac tamponade due to sympathetic stimulation as a compensatory mechanism to maintain adequate cardiac output. (Choice D) Left ventricular outflow obstruction is usually due to critical aortic stenosis or hypertrophic obstructive cardiomyopathy (HOCM). Although this patient has exertional dyspnea, he does not have other findings suggesting aortic stenosis (eg, syncope, systolic murmur). HOCM usually presents at a much earlier age, and its systolic murmur decreases with squatting and increases with straining. (Choice E) Pulmonary hypertension can be due to increased pulmonary arterial pressure (eg, primary pulmonary hypertension) or increased pulmonary venous pressure (eg, left ventricular failure). The cardiac examination usually shows a loud S2 (not muffled sounds). Pulmonary hypertension is typically an indolent process and does not present as right heart failure until late in the disease. Educational objective: Patients with cardiac tamponade usually have clinical features of Beck's triad: hypotension, distended neck veins, and muffled heart sounds. These symptoms are due to an exaggerated shift of the interventricular septum toward the left ventricular cavity, which reduces left ventricular preload, stroke volume, and cardiac output. References: Cardiac tamponade. Pathophysiology, diagnosis, and management. (http://www.ncbi.nlm.nih.gov/pubmed/1811872)

A 53-Year-Old Man Comes to the Physician Complaining of Worsening