What describes the mechanism by which pericardial effusion can cause hemodynamic compromise?

• A. Fluid compresses the heart
• B. It triggers vasodilation
• C. It increases myocardial contractility
• D. It reduces pulmonary pressure

Answer: (A)

The key idea is tamponade physiology: fluid in the pericardial sac exerts external pressure on the heart, especially as it fills in diastole. This compression limits diastolic filling, so preload drops, stroke volume falls, and cardiac output declines, producing hemodynamic compromise. The heart can’t expand normally, pressures in the chambers tend to equalize, and venous return is impaired, which explains the resulting hypotension and signs of poor perfusion. The other options don’t describe this mechanism: vasodilation is a systemic change not driven by the effusion itself; increasing contractility would help circulation rather than cause collapse; and reducing pulmonary pressure isn’t the effect of a pericardial effusion—the issue is external cardiac compression, not lowering lung pressures.