Pericardial effusion

By | 2013-08-05

A build up of fluid in the pericardia] sac results in compression of the heart and progressive diastolic dysfunction. A large volume of pericardial fluid reduces ventricular compliance and therefore limits diastolic filling. Central venous pressure increases and stroke volume and cardiac output decrease. This sequence of events is commonly known as cardiac tamponade. The major causes of different types of pericardial effusion in the dog and cat are summarized in site.

Disorders causing pericardial effusion in the dog

Benign idiopathic pericardial effusion

Benign pericardial effusion is typically a disease of young to middle aged large or giant breed dogs. The aetiology is unknown. Saint Bernards, golden retrievers and great Danes are most commonly affected. Pericardiocentesis usually yields a dark, haemorrhagic, port wine-coloured effusion which fails to clot.

Cardiac and intrapericardial neoplasia

Cardiac neoplasia is often associated with pericardial effusion in older dogs. Primary cardiac tumours are more common in the dog than they are in the cat. The German shepherd is predisposed to right atrial haemangiosarcoma although the tumour may also occur in other breeds. This tumour is extremely malignant and pulmonary metastases are common. Occasionally rupture of the right auricular appendage occurs resulting in acute haemorrhage into the pericardial sac. Heart base tumours (chemodectomas) have a predilection in brachy cephalic breeds such as the boxer. Chemodectomas tend to be locally invasive and rarely metastasize; they may exist concurrently with testicular tumours in some brachycephalic animals. Lymphosarcoma occasionally metastasizes to the heart and results in pericardial effusion. Primary pericardial mesothelioma is an extremely rare malignancy of the pericardial sac.

Right-sided congestive heart failure

A variable volume of pericardial fluid (modified transudate) may be present in some dogs with dilated cardiomyopathy especially those which have pleural effusion and other signs of right-sided failure. Therapeutic drainage of the pericardial effusion is rarely necessary.

Pericarditis and pericardial tibrosis (constrictive pericarditis)

Pericarditis is rare in both dogs and cats. Infection within the pericardial sac results in the development of fibrous adhesions between the epicardium and pericardium which further impair diastolic function. Penetration of the pericardial sac by a foreign body (for example gunshot pellet) may result in septic pericarditis. Sterile inflammatory effusions have been associated with canine distemper, leptospirosis and chronic uraemia.

Intrapericardial cysts

Pericardial cysts have been reported in young dogs and are rare causes of pericardial effusion. Pericardial granulomas may be associated with Actinomyces infection.

Disorders causing pericardial effusion in the cat

In cats with hypertrophic cardiomyopathy pleural effusion and ascites is frequently accompanied by pericardial effusion. Sterile pericardial effusions may occur with systemic infections such as feline infectious peritonitis, toxoplasmosis and occasionally feline panleucopenia. Other less frequent causes include coagulopathics and end-stage renal failure. Cats with end-stage renal failure and pericardial effusion often have evidence of left ventricular hypertrophy, probably due to systemic hypertension. The most common tumour associated with pericardial disease is disseminated lymphosarcoma. Idiopathic pericardial effusions have not been documented.

Clinical signs of pericardial effusion

Pericardial effusion causes signs of low output failure which may progress to cardiogenic shock (weakness, lethargy, exercise intolerance and syncope). Signs of right-sided congestive heart failure tend to predominate with cardiac tamponade because the right ventricular wall, being thinner than the left, is more susceptible to the compressive effects of the pericardial fluid. Ascites may develop rapidly, often within 48 h. The heart sounds are muffled and the femoral pulses weak. Occasionally a rapid fall in pulse pressure may be noted during inspiration (pulsus paradoxicus).

In addition, signs of systemic disease (fever, anorexia and depression) may be apparent with infectious causes of pericardia) effusion. Infection results in the formation of fibrous adhesions and a more gradual limitation in diastolic filling. The pericardial sac becomes thickened and the volume of pericardia] fluid which forms is usually much smaller than with benign idiopathic effusions. Affected animals therefore tend to show signs of mild chronic cardiac tamponade and signs of right-sided failure may be more apparent than signs of low output failure. Friction-type murmurs are rare except during the early stages of pericarditis.

Electrocardiography

Classically, pericardial effusion causes a reduction in R wave amplitude (often less than 1 mv) and electrical alternans. However, it should be noted that these ECG abnormalities occur infrequently and that some giant breed dogs, without any evidence of pericardial disease, may also have low amplirude complexes. Neoplascic infiltration of the myocardium may result in arrhythmias or conduction disturbances.

Radiographic findings

Pericardial effusion results in generalized cardiomegaly and a loss of the normal contours of the cardiac chambers. The heart assumes a globular appearance with a sharp outline, although not infrequently pleural and / or mediastinal fluid may obscure the cardiac silhouette. Additional signs of right-sided failure (hepatomegaly and ascites) may be evident on abdominal radiographs.

Pneumopericardiography

Pneumoperieardiography is a useful technique for detecting the presence of intrapericardial masses, although its use as a diagnostic aid has now been superseded by echocardiography. To obtain reliable results the pericardial effusion should be completely drained and a volume of room air or CO, equivalent to between 50% and 75% of the volume of fluid aspirated injected by syringe. Radiographs are obtained immediately using multiple projections to highlight ditferem areas of the heart.

Echocardiography

Two-dimensional echocardiography is the most sensitive and specific method for detecting pericardial fluid, which appears as an echolucent space between the epicardium and pericardium. The technique is also useful for confirming the presence of pericardial mass lesions / adhesions and assessing the volume of pericardial fluid. The heart should be examined from multiple transducer locations. Serial echocardiographic assessments may be helpful especially for detecting diffuse tumours such as mesotheliomas.

Pericardiocentesis

Pericardiocentesis is often performed on the right side to minimize the risk of puncturing the lungs and the large coronary arteries. In the authors experience, however, the procedure may also be performed safely on the left side. An 8 cm long 16 gauge over-the-needle intravenous catheter ensures the pericardial sac is adequately penetrated for maximal drainage of fluid- The site of entry is usually between the fourth and sixth ribs at a point approximately one quarter the way up the chest wall from the sternum. Having penetrated the pericardium, the fluid is removed using a 50 ml syringe with a three-way valve attached to the catheter. The volume of fluid varies; volumes in excess of one litre are frequently aspirated from large dogs with the idiopathic effusions whereas the volume of fluid in a cat is usually less than 50 ml.

Clinicopathological findings

Pericardial fluid should be submitted for cytological, biochemical and bacteriological examination. Cytological examination of pericardial fluid rarely differentiates neoplastic from non-neoplastic effusions although it may help to rule out infection. Idiopathic d fusions are typically dark, port wine-coloured effusions; they do not clot and are sterile. They contain abundant red blood cells and clusters of reactive mesothelial cells which, because of the degree of Mastic transformation, are difficult to differentiate from neoplastic cells. Occasionally increased numbers of plasma cells and lymphocytes may be seen. The protein content is extremely variable ranging from 9 to 57 gl-1.

Neoplastic effusions and those resulting from acute haemorrhage (for example due to a coagulopathy or a ruptured right atrium) often have a similar appearance although the presence of platelets and macrophages demonstrating erythrophagocytosis may provide a clue that the haemorrhage is more recent. Centrifugation of the effusion and examination of a buffy coat preparation has been advocated as a method to improve the rate of detection of malignant cells. Chemodectomas may yield an effusion which more closely resembles a modified transudate.

True inflammatory exudates are characterized by the presence of increased numbers of nucleated cells and a much higher protein content. They may be classified as septic or sterile. Haematology may show a neutrophilic leucocytosis.

Management of pericardial effusion

Pericardiocentesis should be performed to remove as much of the pericardial effusion as possible. After pericardiocentesis signs of right-sided failure (ascites and pleural effusion) usually resolve within 48 hours and during this period there is often a dramatic reduction in the animal’s body weight. Partial or complete pericardectomy should be considered as an alternative to repeated pericardiocentesis especially if there is rapid recurrence of the effusion. Surgical intervention not only expedites drainage of the fluid but permits biopsy of the pericardial sac or any other mass lesion which may be present. Antibiotics should be administered it the effusion is a septic exudate. The use of corticosteroids is more controversial and is based on the possibility that idiopathic pericardial effusions may have an immune-mediated pathogenesis. The prognosis for most cases of intrapericardial neoplasia is poor.