Keywords: cardiac tamponade, pulsus paradoxus (PubMed Search)
Pulsus paradoxus (exaggerated decrease in BP during inspiration) > 10 mm Hg is a physical exam finding that is often considered diagnostic of cardiac tamponade. The sensitivity of the finding, based on pooled studies, is actually only 82% and specificities are reported as low as 70%. In other words, the presence of the PP does not guarantee the presence of tamponade, and (more importantly) the absence of PP does not rule it out.
Conditions that can mask the presence of PP include hypotension, pericardial adhesions, aortic regurgitation, atrial septal defects, and RVH.
Conditions that can produce a PP in the absence of tamponade include severe COPD, CHF, mitral stenosis, massive PE, severe hypovolemic shock, obesity, and tense ascites.
The bottom line...when you are considering the diagnosis of tamponade, get the bedside ECHO. Don't hang your hat (and the patient's life!) on a pulsus paradoxus.