Pericardial effusion is the accumulation of fluid within the pericardium. The pericardium is a fibrous sac that surrounds the heart and normally contains a very small amount of fluid. When an abnormal amount of fluid accumulates within the pericardium, the sac becomes maximally stretched and the fluid/blood begins to compress the heart. This leads to signs of shock (low blood pressure, elevated heart rate, weakness, pale gums, cold extremities, severe weakness or collapse, and even death). Pericardial effusion can also cause a dog to develop fluid in the chest cavity (pleural effusion) or abdomen (peritoneal effusion/ascites). Significant pericardial effusion is a life-threatening emergency that is treated with a procedure called a pericardiocentesis (see below).

Most cases of pericardial effusion in dogs are caused by a tumor/cancer associated with the heart, which can often be seen on an echocardiogram. However, certain types of cancer like mesothelioma and lymphoma may not form discrete tumors and must be diagnosed on pericardial fluid analysis and/or biopsy of the pericardium. Additionally, small tumors may not be detectable on echocardiogram initially. Other potential causes of pericardial effusion in dogs include idiopathic pericardial effusion (cause cannot be determined), right-sided congestive heart failure, atrial splitting, infection, inflammation and bleeding abnormalities. If an obvious cause for pericardial effusion is not seen on echo, submission of a sample of the effusion for analysis is recommended.

Signs of significant pericardial effusion include weakness (difficulty rising, stumbling), collapse, loss of consciousness, cold limbs, pale gums, labored breathing, increased resting breathing rate, exercise intolerance, vomiting, or abdominal distension. If any of these signs are seen, your pet should be evaluated by a veterinarian immediately.

Significant pericardial effusion requires immediate stabilization via a procedure called pericardiocentesis. Ideally an intravenous catheter is first placed to allow potentially life-saving medications and fluids to be administered as needed. A pericardiocentesis typically requires mild sedation to allow the dog to relax for the procedure. A small amount of a numbing medication is placed at the pericardiocentesis site, and a needle is then passed between the ribs into the pericardial sac. A syringe is used to remove as much of the pericardial effusion as possible, and samples of the pericardial fluid are saved for later analysis if necessary. An ECG is recorded continuously throughout the procedure to monitor for the development of significant cardiac arrhythmias. Pericardiocentesis is generally a safe procedure, although potential complications include arrhythmias, cardiac puncture and, in rare cases, death. If significant pleural effusion (fluid in the chest cavity) is present, this may also be removed to ease breathing. Unless severe, typically abdominal effusion (fluid in the abdomen) is not removed as this should slowly be reabsorbed after the pericardial effusion is resolved. Furosemide and other diuretics are not indicated for the management of pleural or abdominal effusion solely due to pericardial effusion and may cause harmful dehydration.

Although definitive identification of a cardiac tumor type is not possible without obtaining a biopsy sample of the mass (which is difficult to safely perform), a presumptive diagnosis can be made based on the location and echocardiographic appearance of the tumor. Chemodectomas (also sometimes referred to as neuroendocrine tumors or aortic body tumors) are tumors of the chemoreceptors, which are specialized cells that sense oxygen in the blood. Although they tend to be slow growing and don’t often metastasize (spread to distant organs), they can be locally invasive and may cause clinical signs due to compression of surrounding structures. Chemodectomas are also prone to spontaneous bleeding and may lead to pericardial effusion and associated clinical signs.

Unfortunately, the definitive treatment options for chemodectomas is limited. Surgical excision of the tumor would be the ideal treatment, but this is usually not feasible due to the proximity of large blood vessels, nerves, and the heart. Radiation therapy has been used in a small number of cases of chemodectomas to decrease the tumor size and prolong life, but this is rarely curative. Chemotherpay may be considered to try to slow tumor growth.

A pericardectomy is a palliative procedure that should be considered for dogs that have experienced severe pericardial effusion due to a chemodectoma. A pericardectomy involves surgical removal of a large portion of the pericardium (subtotal pericardectomy) or surgical creation of a “window”/hole in the pericardial sac (pericardial window). These procedures allow any blood or fluid to drain into the chest cavity, preventing it from accumulating in the pericardial space and compressing the heart.

As mentioned previously, chemodectomas tend to be slow growing tumors that don’t commonly metastasize, so the prognosis for a dog with this tumor type can be good. If the chemodectoma results in pericardial effusion, and a pericardectomy is performed, the prognosis can be fair to good, with one study reporting a median survival time of 661 days. The dogs with chemodectomas and significant pericardial effusion that did not undergo a pericardectomy survived an average of 129 days.