In the late diastolic phase of cardiac tamponade, what happens to the right atrium (RA)?

During the late diastolic phase of cardiac tamponade, the right atrium experiences significant pressure changes due to the accumulation of fluid in the pericardial space. This condition leads to an increase in intrapericardial pressure which compresses the heart chambers, predominantly affecting the right atrium due to its anatomical positioning and lower pressure within this chamber compared to the left atrium.

As the fluid builds up, the right atrium becomes compressed. This compression can lead to the collapse of the atrial walls as the heart is unable to fill properly during diastole. The diastolic filling pressure on the right side of the heart is impaired, often resulting in decreased right atrial volume and the characteristic finding of right atrial collapse seen on echocardiograms.

Thus, the correct answer reflects the physiological response of the right atrium to the elevated pressures caused by cardiac tamponade, highlighting the critical impact this condition has on atrial dynamics and overall heart function.