| When fluid accumulates in the pericardial sac, the pressure within the sac increases and progressively compresses the chambers of the heart. Because the right ventricular and right atrial diastolic pressures are less than those of the left chambers, the rising intrapericardial pressure first equilibrates with right-sided diastolic pressures, a condition termed
cardiac tamponade. Compression of the right-sided chambers has 2 major consequences: venous return is significantly decreased, causing jugular venous distention and ascites, and blood flow to the lungs is significantly decreased, causing hypoxia and tachypnea. |
| Pericardial effusion is uncommon compared with other acquired cardiovascular diseases and occurs in both small and large animals. There are no breed predilections in cats. Golden Retrievers, Great Danes, and Great Pyrenees are among the most commonly affected breeds of dogs. Overall, most cases involve middle-aged, predominantly male, large- and giant-breed dogs.
Cardiac neoplasia is the most common cause of pericardial effusion in dogs; right atrial tumors are the most frequently seen cardiac neoplasm (usually hemangiosarcoma), followed by heart base tumors (most commonly chemodectoma or ectopic thyroid carcinoma). In cats, the most common cardiac neoplasia is lymphoma. Less common causes of pericardial effusion in dogs and cats are infections (eg, feline infectious peritonitis), trauma, chamber rupture, and secondary to CHF.
Cattle most often develop pericardial effusion secondary to
traumatic reticulopericarditis (
Traumatic Reticuloperitonitis) or cardiac neoplasia (lymphoma). Lymphoma in cattle can also result in valvular insufficiencies. In horses,
septic pericarditis and idiopathic pericarditis are most commonly reported. |
| The severity of clinical signs depends on the rate of pericardial fluid accumulation. Clinical signs include exercise intolerance, anorexia, listlessness, and abdominal swelling (caused by ascites). In horses, there is often a history of respiratory tract infection, fever, anorexia, and depression. Physical examination findings include lethargy, jugular venous distention, muffled heart sounds, and occasionally pericardial friction rubs. Ascites is consistently present in affected
dogs, in which pericardial effusion rapidly develops. With slow development of pericardial fluid, the pericardial sac is able to stretch and clinical signs of right-sided CHF may not develop until severe pericardial effusion is present. |
| CBC, serum chemistry profile, and urinalysis results are usually normal. Mild anemia, neutrophilic leukocytosis, hyperfibrinogenemia, and hyperproteinemia may occur in horses with septic pericarditis and effusion. In horses with suspected septic pericarditis, a culture and sensitivity of the fluid should be performed. In septic pericarditis, there will be a large number of neutrophils with some being degenerate. Protein content of the fluid will be high, and bacteria may be seen.
Cytologic features of idiopathic pericardial effusion in horses are variable, with neutrophils, eosinophils, and macrophages present in variable numbers. Cytologic evaluation of the pericardial fluid is usually not helpful in providing a definitive cause for the pericardial effusion in dogs. |
| Radiographs show an increase in the size of the cardiac silhouette, which takes on a rounded appearance. If the cause is a cardiac tumor, especially a heart base tumor, the cardiac silhouette may appear eccentrically enlarged. The caudal vena cava may be dilated if cardiac tamponade is present. Pleural effusion may also be present if cardiac neoplasia is the cause of the pericardial effusion. The ECG in most cases shows normal sinus rhythm to sinus tachycardia. Occasional atrial
premature and ventricular complexes may occur, especially if neoplasia is the cause. The height of the R waves is often decreased (<1 mV in dogs), and there may be a pattern of alternating variation in R wave amplitude, referred to as
electrical alternans. This results from the swinging motion of the heart within the fluid-filled pericardial sac. Echocardiography is the most sensitive and specific test for the detection of pericardial effusion. A tumor can be visualized in many cases of neoplastic effusion. When cardiac tamponade is present, the walls of the right atrium and right ventricle appear to collapse and flutter. The left-sided chambers are often decreased in size secondary to decreased
venous return from the lungs.
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| Animals with cardiac tamponade require urgent treatment. Medical therapy is typically ineffective at rapidly reducing pericardial effusion. Diuretics are generally contraindicated because they decrease blood volume and cause further collapse of the cardiac chambers. Pericardiocentesis, which is most commonly performed with mild sedation in dogs, should be performed. This is done by placement of a catheter through the chest wall on the right side, just above the costochondral
junction at the fourth to fifth intercostal space. Echocardiography can guide catheter placement at the point where the pericardial sac is closest to the thoracic wall and most distended with fluid. A syringe or extension set with stopcock and syringe (preferred) is attached to the catheter. The system must be closed to air at all times once penetration of the chest wall occurs to avoid creating a pneumothorax. The catheter is passed directly toward the heart while intermittently
aspirating. When the pericardial sac is entered, fluid (usually serosanguineous) flows freely into the syringe. The catheter should be carefully advanced over the needle into the pericardial sac. If arrhythmias develop, withdrawing the needle slightly usually suffices. Antiarrhythmic therapy is rarely needed. As much fluid as possible should be removed from the sac and a sample submitted for analysis. When performing pericardiocentesis in horses, the left fifth intercostal space
should be used in order to avoid the atria, coronary arteries, and right ventricle. Pericardial lavage, with or without antibiotics, is often performed in horses following pericardiocentesis. Pericardiocentesis is relatively easy to perform and serious complications are rare. However, confirming the presence of pericardial effusion by echocardiography is advisable before performing pericardiocentesis. |
| Broad-spectrum antibiotics and parenteral fluids may be given immediately before and after pericardiocentesis. Corticosteroids have not been shown to be beneficial in benign pericardial effusion in dogs, although they have been used with success in horses. Most tumors that cause neoplastic effusion do not respond to chemotherapy. |
| When idiopathic pericarditis is suspected (ie, no mass visible by echocardiography), the owner should be instructed to carefully monitor the animal for any signs of recurrence. Should this occur, a repeat pericardiocentesis is indicated and a subtotal pericardectomy is recommended. Heart base tumors are usually benign in dogs, and if pericardial effusion secondary to a heart base tumor is diagnosed, subtotal pericardectomy should be considered. Many dogs survive symptom-free up to
2 yr following successful subtotal pericardectomy. |
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