Which finding most strongly indicates cardiac tamponade in a patient with acute pericarditis?

• A. Decrease in systolic blood pressure with inspiration (pulsus paradoxus)
• B. Elevated diastolic pressure only
• C. Stable blood pressure with tachycardia
• D. Increased urine output

Answer: (A)

Pulsus paradoxus is the most telling sign of tamponade physiology. When a patient develops tamponade, the accumulating fluid in a restricted pericardial space prevents proper filling of the heart during diastole. During inspiration, increased venous return to the right heart shifts the interventricular septum and reduces left ventricular filling, causing the systolic blood pressure to fall by more than about 10 mmHg. This exaggerated inspiratory drop in SBP is pulsus paradoxus and strongly points to tamponade rather than uncomplicated acute pericarditis.

Other options don’t fit as well. An isolated elevation of diastolic pressure isn’t characteristic of tamponade, which more commonly features impaired filling with pressures that tend toward equilibration across chambers and often hypotension. Stable blood pressure with tachycardia can occur but isn’t specific for tamponade, and increased urine output isn’t related to this condition.