But what we more want to know in the immediate setting is: Is this cardiac tamponade?
You can look for RA systolic or RV diastolic collapse. What if it's equivocal? How good is the clinical exam and EKG in ruling out a tamponade?
Answer: Poor to average, at best. The Beck's triad of hypotension, distended neck veins, and muffled heart sounds are important to remember ... only on tests.
Solution: Think about performing a pulsus paradoxus test to see if it's >12 mmHg. This is a sign of physiologic compromise. Note that the typical cutoff has been 10 mmHg but 12 mmHg is a more specific test.
Take a look at this helpful video demonstrating how to measure pulsus paradoxus.
Thanks to Dr. Hemal Kanzaria for suggesting this JAMA article!
Roy C et al. Does This Patient With a Pericardial Effusion Have Cardiac Tamponade? JAMA: The Journal of the American Medical Association. 2007; 297(16): 1810-8. DOI: 10.1001/jama.297.16.1810