The paradoxical pulse in tamponade: mechanisms and echocardiographic correlates

Pulsus paradoxus is an exaggerated fall in systolic blood pressure with inspiration (usually greater than 10 mm). Understanding the accuracy of pulsus paradoxus for a diagnosis of cardiac tamponade requires a consideration of the mechanisms underlying its genesis, and a knowledge of its presence in other conditions and its variable absence in cardiac tamponade with associated disease states. Echocardiography (M-mode, 2-D, and Doppler) has aided considerably our understanding of pulsus paradoxus. Inspiratory increases in right heart filling and output are widely accepted as necessary for pulsus paradoxus to occur; inspiration causes increases in right ventricular dimensions and pulmonic and tricuspid velocities, and decreases in left ventricular (LV) dimensions and aortic and mitral velocities and LV diastolic compliance. Doppler studies of pulmonary venous inflow confirm that an inspiratory fall in left atrial filling is necessary for pulsus paradoxus. Pulsus paradoxus is complex and multifactorial in origin; it may be absent in cardiac tamponade when certain conditions (e.g., LV dysfunction) coexist and may accompany disease states other than cardiac tamponade (e.g., obstructive airway disease). Thus, the significance of pulsus paradoxus (and its Doppler echo correlates) must be considered in the clinical context.