Pericardial effusion presents clinicians with a challenge when diagnosing the underlying cause, since the prognosis can be
favorable in certain cases. Partial pericardectomy can be performed via thoracoscopy; and in select cases, this minimally
invasive procedure can provide long-term relief of clinical signs.
There are many potential causes of pericardial effusion, but the most common is intrapericardial neoplasia, particularly right
atrial hemangiosarcoma and aortic body tumor. Other less-common neoplastic causes of pericardial effusion include ectopic
thyroid neoplasia, lymphosarcoma, mesothelioma, rhabdomyosarcoma and metastatic neoplasia. Idiopathic pericardial effusion
(IPE) is diagnosed when no other cause of effusion is found. Rare causes of pericardial effusion include congestive heart
failure, left atrial tear or cardiac trauma, coagulopathy, infection (although coccidiodiomycosis is more common in some geographic
locations), foreign body and chronic uremia.
As pericardial fluid accumulates, it will compress the heart, known as tamponade, resulting in poor ventricular filling. The
right side of the heart has lower pressures than the left side and is primarily affected by tamponade. In chronic cases, this
leads to signs of right heart failure. When pericardial fluid forms acutely, the pericardium is minimally distensible and
tamponade can be severe even with relatively small volumes of fluid, resulting in reduced stroke volume and systemic hypotension.
Middle-aged to older large-breed dogs, including retrievers and German Shepherds are most commonly presented. Brachiocephalics
may be over-represented with chemodectomas. The history can include acute collapse or a longer period of clinical signs such
as lethargy, weakness, inappetance, exercise intolerance, tachypnea and abdominal distension. Physical examination often reveals
pallor, slow capillary refill time, weak arterial pulses, weakness, tachypnea, tachycardia and muffled heart sounds. If the
pericardial effusion has formed acutely, the patient can be profoundly weak or recumbent with circulatory collapse. In chronic
pericardial effusion, there often are signs of right heart failure, including jugular vein distension, ascites and possibly
tachypnea due to pleural effusion. Pulmonary edema is not expected.
Thoracic radiographs reveal mild to severe enlargement of the cardiac silhouette, which is usually globoid with loss of the
typical contours. In some cases, there may be enlargement of the caudal vena cava and/or pleural effusion. Metastatic pulmonary
lesions may be detected by thoracic radiographs or CT scan. An ECG often shows sinus tachycardia. Arrhythmias are possible.
There will be low-voltage QRS complexes (<1mV) in about 50 percent of cases. Electrical alternans (EA) describe a regular
variation in QRS-T wave height or morphology resulting from the heart swinging back and forth within the pericardial sac.
Electrical alternans may be present in less then 20 percent of cases, but the presence of EA and the above clinical signs
are strongly suggestive of pericardial effusion. Echocardiography is very sensitive for diagnosing pericardial effusion (Photo
1), and is useful for detection of intrapericardial masses, and is always recommended.
Photo 1: This is an echocardiogram image showing the long axis view from the right parasternum. Pericardial effusion is
surrounding the heart. PE = pericardial effusion, RV = right ventricle, RA = right atrium, LA = left atrium, LV = left ventricle
Most masses are easier to detect with the presence of the pericardial effusion. It is not always possible to differentiate
idiopathic pericardial effusion from neoplastic causes since there is often no discrete mass with mesothelioma or lymphoma.
Occasionally, hemangiosarcoma lesions too small for echocardiographic detection can be the source of the hemorrhagic effusion.
Analysis and cytology of the pericardial fluid can be performed but is unlikely to provide a definitive diagnosis except when
an infective cause is present. Intrapericardial tumors often exfoliate poorly, except for lymphosarcoma, which is very rare.
Neoplastic mesothelial cells are hard to differentiate from reactive cells. Biochemical parameters, pH and PCV have been studied
but are not reliably able to differentiate neoplastic from IPE in an individual case. The pericardial fluid is usually hemorrhagic,
the PCV can be high in IPE and hemangiosarcoma, chemodectomas typically have lower PCV. There is recent data that a serum
biomarker, cardiac troponin-I, may differentiate cardiac hemangiosarcoma from IPE in dogs. Other types of neoplasia have not
been evaluated with this biomarker.