One of the major indications for bedside cardiac ultrasound is the detection of pericardial effusion and its extreme form, cardiac tamponade. You may remember that Beck’s Triad (hypotension, jugular venous distension, and muffled or distant heart sounds) is pathognomonic for cardiac tamponade. You should also remember (to say to your colleagues who recite that tamponade is a clinical diagnosis) that the triad is present in about one-third of cases.
If you can spot tamponade clinically in a hypotensive, tachycardic patient with muffled heart tones and JVD, congratulations! You may pass your boards, save a simulated patient, or impress a junior medical student. But how does one diagnose this condition a bit earlier in its natural history?
Pulsus parodoxus is not as hard to assess as it sounds- inflate a blood pressure cuff as you normally would. Slowly deflate the cuff and listen for Korotkoff sounds. If they are present during inspiration and expiration, there is no pulsus parodoxus and you are done. If you only hear Korotkoff sounds during expiration, note the pressure reading and keep slowly deflating until they are present throughout the respiratory cycle. What is the pressure difference between sounds during expiration only and sounds throughout the entire cycle? If it is greater than 10 mmHg, pulsus paradoxus is present.
But you read this far down because you want to know how to find tamponade using ultrasound, right? There are some earlier findings of cardiac tamponade which are detectable with ultrasound before hemodynamic instability ensues. They are:
- Pericardial effusion
- Hard to have tamponade without this
- Diastolic collapse of right atrium and right ventricle
- Ideally diastole can be recognized with EKG monitoring on ultrasound, or using M-Mode
- Inferior Vena cava plethora
- Dilated IVC with loss of respiratory variation
- Atrio-ventricular valve Doppler inflow velocities
- If these words are unfamilar, use the first three findings instead! Respiratory variation in inflow across the atrioventricular valves (like a valvular pulsus parodoxus) can be a sign of early tamponade physiology. However this is an advanced technique.
The video below shows the first three findings nicely:
Large Pericardial Effusion from Sinai EM Ultrasound on Vimeo.
Note the subxiphoid view with large effusion, followed by the parasternal long axis view. Finally, a transverse view of the IVC demonstrates dilatation and loss of respiratory variation.
 Further Reading:
- Schairer JR, Biswas S, Keteyian SJ, et al. A systematic approach to evaluation of pericardial effusion and cardiac tamponade. Cardiol Rev. 2011 Sep-Oct;19(5):233-8.
- Nagdev A, Stone MB. Point-of-care ultrasound evaluation of pericardial effusions: does this patient have cardiac tamponade? Resuscitation. 2011 Jun;82(6):671-3.