Introduction: Neoplasia and idiopathic pericarditis are the most common causes of pericardial effusion. Echocardiography is the preferred clinical diagnostic test for pericardial effusion and tamponade. Determining the underlying cause is pivotal for treatment and prognosis. The reported incidence of cardiac neoplasia in dogs with pericardial effusion varies between 30% to 62%. Our aim was to evaluate diagnosed underlying etiologies at our institution.

Methods: All dogs echocardiographically diagnosed with pericardial effusion by a single cardiologist from 2008 until January 2019 were included. The presence of cardiac tamponade and echocardiographical diagnosis of underlying etiology were recorded. The incidence of underlying etiologies was compared between cohorts presented prior to and after 2014.

Results: 82 cases of pericardial effusion (70 with cardiac tamponade) were included. Underlying etiology in cardiac effusion and cardiac tamponade were neoplasia (53 vs. 49), idiopathic (17 vs. 16), and ‘other’ (12 vs. 5). ‘Other’ causes were 6 dogs with right-side congestive heart disease (1 tamponade), 4 atrial ruptures (2 tamponades), 1 coagulopathy and 1 peritoneal-pericardial hernia (both tamponades). Before 2014, 15 cardiac tamponades were recorded, 60% (9/15) with neoplasia and 40% (6/15) idiopathic. After 2014, in 55 cardiac tamponade cases, 72% (40/55) displayed neoplasia, 19% (10/55) were idiopathic, 9% (5/55) due to other causes (listed above).

Discussion: Echocardiography is accepted as clinical reference diagnosis when performed by a cardiologist for the diagnosis of pericardial effusion and underlying etiology. Right sided congestive heart failure appears to be a rare cause of cardiac tamponade. The incidence of neoplasia in dogs with pericardial effusion or tamponade was 64,5% (53/82) or 70%(49/70). The incidence of cardiac tamponade due to neoplasia before 2014 (60%; 9/15) was lower than after 2014 (72%; 40/55). This difference could be due to the increased ability of the observer to detect neoplasia, or be a coincidence. Technical improvements however seem unlikely, as the same machine was used throughout the study.

Conclusion: Cardiac tamponades of neoplastic origin appear more common than described. Atrial ruptures do not always present with tamponade, while right sided congestive heart disease may induce tamponade. Findings of this study must be confirmed in multicenter studies before drawing conclusions.