Because the use of echocardiography in the evaluation of cardiac disorders has become routine, a growing number of patients have been diagnosed with pericardial effusion. The possible causes of pericardial effusion are numerous. However, even after an extensive medical evaluation, some patients are left with a diagnosis of “idiopathic” pericardial effusion. Despite its increased frequency in diagnosis, the natural history, clinical course and management of this condition have not been well defined. Sagristà-Sauleda and colleagues performed a long-term prospective study to determine the clinical course of pericardial effusion and the need for intervention in patients with this condition.

Patients were considered to have idiopathic pericardial effusion if they met all of the following criteria: the cause of pericardial effusion was undetermined after a complete medical evaluation, including examination of the pericardial fluid or tissue; the sum of the anterior and posterior echo-free spaces exceeded 20 mm at end diastole; the disease did not progress during the observation period; and the effusion persisted for more than three months. Cardiac tamponade was diagnosed if the systolic blood pressure was less than 90 mm Hg, pulsus paradoxus was present and jugular venous pressure had increased.

Patients with suspected idiopathic pericardial effusion were prospectively enrolled between 1977 and 1992. The clinical evaluation included a complete medical history, physical examination, electrocardiography, chest radiography and echocardiography; see the accompanying table for features of the laboratory evaluation. Finally, sputum or gastric aspirates were evaluated for acid-fast bacilli.

Patients underwent pericardiocentesis in the cardiac catheterization laboratory with subsequent chemical and bacteriologic evaluation of the pericardial fluid. If the pericardial effusion reappeared, a second pericardiocentesis was done. An anterior pericardiectomy was performed if the pericardial effusion reoccurred and lasted for more than six months. After the initial pericardiocentesis, patients were seen every three months for one year and then annually. Patients who became symptomatic were seen on an acute basis.

The researchers evaluated 1,108 patients with pericarditis from any cause; 461 patients had large pericardial effusions. Eventually, 28 patients met the criteria for idiopathic disease and were included in the study. Nineteen women and nine men with a median age of 61 years participated in the study. Thirteen of the patients were initially asymptomatic, seven presented with atypical chest pain and seven were admitted to the hospital with overt cardiac tamponade. The duration of the effusions ranged from six months to 15 years. In all patients, the evaluation of pericardial fluid was normal or nondiagnostic.

Follow-up ranged from 18 months to 20 years. During follow-up, five patients underwent early pericardiectomy because of the presence of symptoms or the recurrence of a large effusion. Pericardiocentesis alone fully resolved or significantly reduced the pericardial effusion in eight patients. Ultimately, 20 of the 28 patients underwent pericardiectomy with no associated mortality. Only two patients required the procedure to treat overt tamponade.

The authors note several key points from their study. First, idiopathic pericardial effusion is generally rare in patients who present with pericarditis; effusion occurred in only 2.2 percent of the patients in this study. However, determination of a cause may require extensive diagnostic work-up. Tuberculosis and neoplasms are not common causes of pericardial effusion, although rare occurrence has been documented. Therefore, the authors believe that tuberculosis does not need to be aggressively ruled out in these patients. Pericardial drainage can effectively resolve the effusion in most cases; in this study, 42 percent of patients did not have an initial recurrence. Patients who are asymptomatic after initial evaluation could be followed with serial echocardiography; however, overt tamponade may occur unexpectedly. Thus, pericardiocentesis should be performed in most patients. Anterior pericardiectomy should be considered in patients with recurrence of fluid or those who develop symptoms of tamponade.