CHAPTER EIGHT

Pericardial Disease, Effusions, and Masses

The reported causes of pericardial effusion (PE) in animals include pericardioperitoneal hernias, congestive heart failure, left atrial rupture, infection, neoplasia, trauma, and benign idiopathic causes (1–5). The pericardial effusion may lead to tamponade (6).

Feline infectious peritonitis (FIP) is the most common cause of pericardial effusion in the cat and is often accompanied by pleural effusion and ascites. Hypertrophic cardiomyopathy is the most frequent form of heart disease leading to pericardial effusion in cats (5). Other less-encountered forms of heart disease resulting in PE in the cat include dilated and restrictive cardiomyopathies, and mitral valve abnormalities (7,8).

Intrapericardial neoplasia, idiopathic hemorrhagic pericarditis, and left atrial rupture secondary to chronic mitral regurgitation are the most common causes of pericardial effusion in the dog, with intracardiac and pericardial tumors heading the list (9). Of these tumors, hemangiosarcoma, chemodectoma, and mesothelioma lead the list for highest incidence (10).

Pericardial Effusion

There is a high incidence of pericardial effusion in large breed dogs with the highest incidence seen in golden retrievers, German shepherd dogs, Saint Bernards, Labrador retrievers, and Newfoundlands (11–14). Most dogs that present with pericardial effusion with echocardiographic evidence of a mass are older (median age 9–11 years) than dogs that present without echocardiographic evidence of a mass (median age 7–9 years). The exception is the Saint Bernard, which presented at a much younger median age of 2.3 years (11). Congestive heart failure may also cause pericardial effusion in both dogs and cats, although the incidence is less common and the amount of effusion is typically small (1,5,11,15–19). Occasionally atrial rupture causes pericardial effusion in dogs (15).

Pericardial effusion in the cat is relatively rare. When present however, several studies have shown that congestive heart failure secondary to hypertrophic, restrictive, and unclassified cardiomyopathy are the most common underlying causes of pericardial effusion in cats (5,15,17,20,21). Feline infectious peritonitis, neoplasia, pericardial peritoneal diaphragmatic hernia, systemic infections, and uremia, are other reported causes of pericardial effusion in cats. Of these, neoplasia, primarily lymphoma, and adenocarcinoma and FIP are reported as the next most common causes of effusion in the cat (5,7,8,15–19,22–24).

Fibrinous pericarditis is the most common underlying etiology of pericardial effusion in the cow. Other causes of bovine pericardial effusion include cardiac lymphoma and effusion secondary to spread from systemic, pleural, and respiratory infection (25–27).

Echocardiographic Features of Pericardial Effusion

Echocardiography is the procedure of choice when trying to diagnose the presence or absence of

pericardial effusion (28). The echocardiographic features of pericardial effusion in all animals include the presence of an echo free or hypoechoic space between the epicardium and the pericardial sac, swinging motion of the heart when the amount of effusion is significant, and if tamponade is present, diastolic collapse of the right atrium or ventricle (3,5,28–30). Pericardial effusion is typically not seen behind the left and right atrium on echocardiographic images since the parietal and visceral pericardiums are more adherent to each other at the base of the heart (Figures 8.1, 8.2, 8.3, 8.4, 8.5). This helps differentiate pleural from pericardial effusions (31). The boundaries of pericardial effusion are typically smooth and conform to the shape of the heart while pleural effusion is seen as more irregular with ill-defined boundaries. In man, an echo-free space of less than 5 mm is considered to be a mild effusion, a space between 5 and 10 mm is moderate in amount, and an anechoic space of greater than 10 mm is classified as a severe amount of fluid accumulation (28).

Pericardial effusion is typically not seen at the heart base below the atria while pleural fluid is present.

Figure 8.1 An echo-free space below the left ventricular wall in this parasternal four-chamber view representative of pericardial effusion is seen in this dog with congestive heart failure. Notice that the pericardial fluid is not seen at the heart base and stops just beyond the atrial and ventricular junction. RV = right ventricle, RA = right atrium, LV = left ventricle, LA = left atrium, PE = pericardial effusion.

Figure 8.2 The large echo-free space of pericardial effusion surrounds the heart of this dog with idiopathic pericardial effusion. Notice that the fluid does not extend around the base of the heart and its boundaries are relatively smooth and circular. PE = pericardial effusion, RV = right ventricle, LV = left ventricle, LA = left atrium, RA = right atrium, plane = right parasternal four chamber.

Figure 8.3 The left auricle is seen within the pericardial space in this dog with effusion (arrow). RV = right ventricle, LV = left ventricle, RA = right atrium, LA = left atrium, plane = right parasternal four chamber.

Figure 8.4 The left auricle may be seen within the pericardial fluid next to the left ventricle on transverse images. LAU = left auricle, PE = pericardial effusion, RV = right ventricle, LV = left ventricle, plane = right parasternal transverse view at the level of the chordae.

effusion, VS = ventricular septum, LV = left ventricle, LVW = left ventricular wall.

Large amounts of thoracic or mediastinal fat have sometimes been misdiagnosed as pericardial effusion, and care should be taken to set the gain correctly and to image multiple cardiac planes (31). The diagnosis of pericardial fat is typically made when an anechoic space is seen in the near field of the sector image, and although it may be present in the far field, it usually is not. Therefore, an echofree space in both the near field and far field usually supports the diagnosis of true pericardial effusion, but this is not foolproof as pericardial fat can occasionally be seen in both areas (28,32,33). Fat when present typically moves with the heart during contraction, and is somewhat echogenic, features that can help differentiate fat from pericardial effusion (28).

Cardiac Tamponade

Pericardial fluid accumulation that causes intrapericardial pressure to be higher than or equal to right ventricular pressure results in diastolic collapse of the right ventricle and atrium, decreased cardiac output, and signs of forward failure (21,34–36). The amount of pericardial fluid does not determine whether tamponade is present or not. Intrapericardial pressure is determined by pericardial compliance, the rate of fluid accumulation, and the amount of fluid accumulation (30). The compliance of the pericardial sac decreases with age, with chronic pericardial inflammation, and with pericardial neoplasia, so smaller amounts of fluid are needed to generate large amount of pressure on the cardiac chambers (30). Additionally a chronic slow-developing effusion is less likely to develop tamponade (3,21,37,38). Dogs that present with the clinical sign of collapse typically have tamponade and have a high incidence of being positive for the presence of cardiac neoplasia. The collapse is thought to occur because of a rapid accumulation of fluid secondary to the neoplastic lesion (14). Dogs that are diagnosed with idiopathic effusions tend to accumulate larger volumes of effusion before tamponade develops presumably because of the slow and chronic nature of fluid accumulation, which allows the pericardial sac to expand slowly, delaying the development of high pressure within the pericardial space (13). Signs of right heart failure including jugular distension and ascites instead of collapse typically suggest slow fluid accumulation (21,39).

The size of the effusion does not determine whether tamponade is present. Diastolic collapse of the right atrium and/or