Pericardial effusions occur in about 50% of patients with acute pericarditis. The patient may be asymptomatic despite a very large pericardial effusion if it occurs slowly, allowing the pericardium to stretch. Tamponade, however, may result if as little as 100 ml of fluid enters the pericardial space rapidly and significantly impairs cardiac filling.

Patients who have pericarditis with tamponade commonly present with a history of an underlying malignancy or recent cardiac surgery. They usually present with signs and symptoms of hypotension, dyspnea and edema due to reduced cardiac output and elevated filling pressures.

The physical examination typically reveals an abnormal pulsus paradoxus, defined as an inspiratory decrease in blood pressure greater than 10 mmHg. This is caused by high intrapericardial pressures limiting total cardiac filling capacity combined with an increase in right sided volume during inspiration that results in an obligatory decrease in left heart filling. There is also an increased jugular venous pressure and, at times, a prominent "x" descent and diminished heart sounds.

We will now discuss the proper technique to check for pulsus paradoxus. First, take a rapid blood pressure to get a general sense of the systolic blood pressure. Then inflate the cuff 20 mmHg above the first Korotkoff sound. Slowly deflate the cuff and listen to where you hear the first Korotkoff sound. At that point, you should be able to hear the sound disappearing with inspiration. Continue to allow the pressure to fall and note when you can hear the first Korotkoff sound throughout the entire respiratory cycle. The difference in these two readings is the pulsus paradoxus. Pulsus paradoxus can also be seen in respiratory distress, such as COPD and acute pulmonary edema with severe left ventricular dyscfunction.