Chapter 44 Pericardial Diseases
INTRODUCTION
The clinical picture, pathophysiology, and therapeutic approach to acute pericardial effusion are covered in Chapter 43, Cardiac Tamponade and Pericardiocentesis. This chapter focuses on the differential diagnosis for canine and feline pericardial disease (Boxes 44-1 and 44-2) and details the more common causes of pericardial effusion in the dog.
Box 44-1 Pericardial Diseases in the Dog
CLINICAL SIGNS
The clinical signs associated with pericardial effusion will depend on the magnitude and rate of elevation of intrapericardial pressures. This will be determined chiefly by the volume of fluid within and the distensibility of the pericardial sac. Acute pericardial hemorrhage (hemangiosarcoma, left atrial tear) will typically result in signs of cardiac tamponade (see Chapter 43, Cardiac Tamponade and Pericardiocentesis) with lower volumes than those seen with causes associated with slower accumulation (idiopathic pericarditis, malignant mesothelioma [MM]). Accordingly, patients brought in for collapse have a worse long-term prognosis.1 In addition, signs of right-sided congestive heart failure (jugular distention, ascites, pleural effusion) suggest a more chronic fluid accumulation, allowing time for cavitary fluid retention. Ascites has been correlated with a better long-term prognosis.1 Disease processes associated with fibrosis of the pericardial sac will lead to clinical signs with lower volumes of effusion. In some cases (constrictive pericarditis) clinical signs are present even in the absence of pericardial effusion. Space-occupying lesions of the pericardial sac (pericardial cysts, peritoneopericardial diaphragmatic hernia) may result in right-sided congestive heart failure or cardiac tamponade, particularly with accompanying pericardial effusion.
SIGNALMENT
Golden Retriever dogs are significantly overrepresented for all major causes of pericardial effusion: hemangiosarcoma (HSA), idiopathic pericardial effusion (IPE), MM, and heart base tumor (HBT).1–9 German Shepherd dogs are one of the breeds in which right atrial HSA and HBT are more common.3,10–12 Boxers and other brachycephalic breeds traditionally are reported to be more predisposed to HBT, but in more recent reports Golden Retrievers and Labrador Retrievers were more commonly affected.2,3,8,9 Saint Bernards and Labrador Retrievers are reported to be overrepresented for IPE, and Cocker Spaniel dogs and Labrador Retrievers may be overrepresented for MM (Laste, unpublished data).2,8 Younger patients are at higher risk for congenital diseases (peritoneopericardial diaphragmatic hernia, pericardial cysts), and middle-aged to older patients are at higher risk for neoplastic causes.3,13 Male dogs are more likely to develop IPE per most reports.1,2,6,8,10 There is no reported sex predilection with neoplastic causes of pericardial effusion, but intact animals, particularly intact females, have a significantly lower incidence of cardiac tumors.3
HISTORY
The history may help determine the likelihood of acute hemorrhage (hemorrhage from a tumor) versus a more chronic accumulation of pericardial effusion more typically associated with the insidious disease processes (IPE, MM). Travel history, history of trauma, or possible rodenticide exposure may be important in forming the differential diagnosis list for each patient. A history of preexisting valvular disease will raise the index of suspicion for the possibility of left atrial rupture with acute hemopericardium. In addition, previously diagnosed pericardial disease and the chronicity of the effusion may make some diagnoses more likely than others. Patients surviving longer than 7 months are unlikely to have HSA.1 The longer the survival, the more likely it is that IPE is present.
DIAGNOSTIC FINDINGS
Laboratory Findings
Laboratory findings are not specific for most cases of pericardial effusion aside from marked azotemia in patients with uremic pericarditis. Increases in circulating nucleated red blood cells have been reported in patients with right atrial HSA, but this has not been substantiated by other sources.10 Anemia may be noted in the patient with pericardial effusion, regardless of the underlying cause, but this has not been reported consistently.2,10
Radiographic Findings
Radiographic findings are variable. Heart size may be remarkably normal in patients with acute hemopericardium. The caudal vena cava usually is distended, suggesting elevated right atrial pressures. In cases of chronic-accumulation pericardial effusion, the heart may have the globoid “basketball” appearance classically described. Mass lesions may be suggested by bulges at the heart base. Pulmonary metastases may be noted in some cases with cardiac neoplasia. With more chronic disease, pleural effusion may be present and may obscure the cardiac silhouette and pulmonary parenchyma. Patients with peritoneopericardial diaphragmatic hernia (PPDH) show confluence of the cardiac silhouette and the diaphragm and, depending on the extent of organ involvement, the abdominal cavity may appear devoid of abdominal contents. If there are gastrointestinal segments within the pericardial sac, there may be a suggestive gas pattern, but omental fat and liver are more typically herniated through the defect. Sternal defects may be noted and, if present, are suggestive of a PPDH. Metallic foreign bodies are an uncommonly reported cause of pericardial effusion and can be noted on thoracic radiographs.14
Electrocardiographic Findings
Low-amplitude QRS complexes are the most consistently reported electrocardiographic finding.2,4,10 Although electrical alternans (beat-to-beat variations in the R wave amplitude) is described as a classic finding with pericardial effusion, this is reported only 6% to 37% of the time.2,10 Electrical alternans is associated with higher volumes of pericardial effusion and is thought to be related to the heart swinging within the fluid-filled pericardial sac. ST segment changes, and ventricular or supraventricular arrhythmias may be present in patients with cardiac tamponade.2,4,7,9
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