What physiologic event is most responsible for pulsus paradoxus in a patient with acute pericardial tamponade?

Pulsus paradoxus is a clinical phenomenon often observed in conditions such as acute pericardial tamponade, where a significant drop in blood pressure occurs during inspiration. This event is primarily attributed to the shift of the interventricular septum.

In acute pericardial tamponade, the accumulation of fluid in the pericardial space restricts the heart's ability to expand and fill appropriately during diastole. During normal respiration, the negative intrathoracic pressure created during inspiration facilitates increased venous return to the heart. However, in the presence of pericardial tamponade, this increased venous return can lead to a displacement of the interventricular septum towards the left ventricle, compromising the filling of the right ventricle.

As the right ventricle fills inadequately due to this mechanical shifting, the stroke volume decreases, which in turn results in a drop in systemic arterial pressure noted as pulsus paradoxus. This dynamic interplay between the chest pressure changes during respiration and the restrictive effects of the fluid in the pericardial space directly creates the characteristic fall in blood pressure during inspiration.

Thus, the shift of the interventricular septum is the physiologic event that significantly contributes to the