Objective Aim of this paper is to evaluate the outcomes of ‘idiopathic’ chronic large pericardial effusions without initial evidence of pericarditis.

Methods All consecutive cases of idiopathic chronic large pericardial effusions evaluated from 2000 to 2015 in three Italian tertiary referral centres for pericardial diseases were enrolled in a prospective cohort study. The term ‘idiopathic’ was applied to cases that performed a complete diagnostic evaluation to exclude a specific aetiology. A clinical and echocardiographic follow-up was performed every 3–6 months.

Results 100 patients were included (mean age 61.3±14.6 years, 54 females, 44 patients were asymptomatic according to clinical evaluation) with a mean follow-up of 50 months. The baseline median size of the effusion (evaluated as the largest end-diastolic echo-free space) was 25 mm (IQR 8) and decreased to a mean value of 7 mm (IQR 19; p<0.0001) with complete regression in 39 patients at the end of follow-up. There were no new aetiological diagnoses. Adverse events were respectively: cardiac tamponade in 8 patients (8.0%), pericardiocentesis in 30 patients (30.0%), pericardial window in 12 cases (12.0%) and pericardiectomy in 3 patients (3.0%). Recurrence-free survival and complications-free survival was better in patients treated without interventions (log rank p=0.0038).

Conclusions The evolution of ‘idiopathic’ chronic large pericardial effusions is usually benign with reduction of the size of the effusion in the majority of cases, and regression in about 40% of cases. The risk of cardiac tamponade is 2.2%/year and recurrence/complications survival was better in patients treated conservatively without interventions.