cardiac tamponade

Cardiac tamponade is what happens when fluid in the pericardial sac builds up enough to squeeze the heart from outside, so its chambers cannot fill properly between beats. Imagine trying to inflate a balloon inside a tightly sealed jar: as the jar fills with water, there is no room left for the balloon to expand.

Because the heart cannot fill, it cannot pump out a normal stroke volume, so blood backs up in the veins while the output to the body falls. Classic findings, sometimes called Beck's triad, are low blood pressure, distended neck veins, and muffled heart sounds. An exaggerated drop in blood pressure during inspiration, known as pulsus paradoxus, is another key sign.

Tamponade is a medical emergency. Echocardiography typically shows the effusion plus collapse of the right-sided chambers when their pressure is lowest. The definitive treatment is to drain the fluid, usually by pericardiocentesis with a needle, or surgically; relieving even a modest volume can rapidly restore filling and blood pressure.