Chapter 151 Pericardial Diseases
The pericardium consists of two mesothelial-lined membranes: the visceral layer (epicardium) that is tightly adhered to the myocardium and the reflection of this membrane that forms the parietal pericardium. Between these is a space that contains the heart, origins of the major arteries, and terminations of the vena cava and pulmonary veins. The normal pericardial space also contains a very small amount of serous, lubricating pericardial fluid. The normal pericardium limits acute cardiac dilatation, maintains cardiac geometry, contributes to ventricular compliance and interdependence, reduces friction, and provides a barrier from inflammation. The pericardium is not essential to survival and can be removed surgically.
Pericardial disease is one of the most common causes of right-sided heart failure in the dog. In older dogs, cardiac or heart-base neoplasia is a common etiology.
PERITONEOPERICARDIAL DIAPHRAGMATIC HERNIA
PPDH is a defect in the embryologic septum transversum that separates the peritoneal from the pericardial space. Defects permit direct communication of abdominal organs or tissue with the heart. PPDH is relatively common in cats and also can develop in dogs. (Weimaraner dogs and schnauzers are predisposed.) Males may be predisposed. Himalayan and domesticated long-haired cats were more likely to be affected by PPDH in one study.
In cats, it is typical for the hernia to contain mainly fat with one or more lobes of liver. In the dog the hernia may be subtle, containing only falciform fat, or there may be liver or loops of intestine contained.
Clinical Signs
Many affected dogs and cats are without overt clinical signs, unless the hernia is large and there is a large volume of herniated abdominal content within the thorax. Infrequently, liver strangulation may lead to signs of discomfort.
Diagnosis
Physical Examination
Diagnostic Imaging
Treatment
Treatment of PPDH is surgical and optimally accomplished at the time of spay/neuter. Surgical results have indicated a very favorable outcome. However, a PPDH often is an incidental finding in mature animals, and in these cases, surgical intervention may not be warranted unless intestines are contained within the thorax or the risk of herniation is deemed high. Consultation with an experienced surgeon can be helpful in these patients.
Cardiac tamponade is a rare complication of PPDH. Entrapment of a loop of bowel or strangulation of the liver requires prompt recognition and surgical management.
PERICARDIAL EFFUSION
Etiology
Pathophysiology

Figure 152-2 Diagrammatic representation of pericardial effusion. See text for explanation. A, aorta; ABP, arterial blood pressure; CVP, central venous pressure; JVP, jugular venous pressure; LAP, left atrial pressure; LV, left ventricle; LVDP, left ventricular diastolic pressure; PA, pulmonary artery; Pr, pressure; RAP, right atrial pressure; RVDP, right ventricular diastolic pressure; VC, vena cava.
Diagnosis
The clinical diagnosis of PE follows a logical course from history and physical examination to selection of diagnostic tests. These studies should establish the diagnosis, etiology, and clinical significance of a PE. The electrocardiogram, thoracic radiography, fluoroscopy, abdominal ultrasonography, and echocardiography offer complementary information.
Pericardiocentesis can be both diagnostic and therapeutic in this disorder. Diagnosis in some patients requires surgical exploration with biopsy of the pericardium or surrounding tissues.
Signalment
PPDH is more common in young dogs and cats but may be an incidental finding in older animals. Dogs >7 years of age are more likely to develop cardiac or heart base neoplasia. Golden retrievers and St. Bernard dogs are predisposed to idiopathic pericardial hemorrhage; brachycephalic breeds to chemodectoma; golden retrievers, Labrador retrievers, German shepherds, and many other breeds to hemangiosarcoma; golden retrievers to mesothelioma.
History
Collapse or syncope are particularly common signs with acute cardiac tamponade (e.g., sudden hemorrhage). Dogs with a history of sudden collapse are more likely to have an underlying neoplastic cause. Syncope also can occur after diuretic therapy of right-sided congestive heart failure (because elevated venous pressures are needed to maintain cardiac filling and cardiac output and this compensation is lost with volume depletion).
Physical Examination
Laboratory Tests
Electrocardiogram
An electrocardiogram may show any of the following:

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