Pericardial disease in small animals is relatively uncommon, but its presence may be life-threatening. More commonly seen in dogs than in cats, the clinical signs of pericardial disease in both species can be easily overlooked or mistaken for those of other disease processes. In patients with life-threatening pericardial effusion, which has led to cardiac tamponade, it is important for you to rapidly identify and treat the elevated intrapericardial pressure. In this article, we discuss pericardial disease in dogs and cats, with a special emphasis on its diagnosis and treatment.
(Illustration by Paul Petersen)
DISEASE OVERVIEW AND CAUSES
The pericardium of dogs and cats is normally a paper-thin, translucent membrane attached at the heart base. This membrane provides the heart with a sac-like protective compartment. The normal pericardial sac contains 2 to 10 ml of clear, thin, serous fluid that acts primarily as a lubricant.1 Pericardial effusion is defined as an abnormal accumulation of fluid in the pericardial sac. If the intrapericardial pressure exceeds the pressure within the right atrium, cardiac tamponade—acute compression of the heart and impairment of ventricular filling due to increased intrapericardial pressure—may develop (Figure 1).2 When pericardial effusion is present, administering a diuretic such as furosemide will worsen the patient's cardiac output by reducing cardiac preload. Physically removing clinically significant effusions from the pericardial or pleural space as soon as possible is vital for the patient's health. In general, diuretic therapy should not be used to remove significant body cavity fluid accumulation.
Pericardial effusion can be caused by either congenital or acquired disease. The most common etiologies are listed below in decreasing order of frequency.
1. A long-axis echocardiogram obtained from the right parasternal window in a dog. Note the marked pericardial effusion (PE) and collapse of the right atrium (RA) due to increased intrapericardial pressure. Decreased RA filling leads to reduced right ventricular (RV) filling and diminished cardiac output.
Cardiac neoplasia is extremely rare in cats, with lymphoma being the most common diagnosis.3 Although cardiac neoplasia in dogs is also rare, one survey of the Veterinary Medical Database reports that 0.19% of all canine tumors are cardiac, and these tumors are the most common cause of pericardial effusion in dogs.4 Hemangiosarcoma and aortic body tumors (e.g. chemodectoma) are the two most common types of tumors leading to pericardial effusion in dogs, followed by mesothelioma.4 Hemangiosarcoma is by far the most common.4
Prognosis depends on the type of tumor. Hemangiosarcomas have much more aggressive biology than aortic tumors or mesotheliomas and are likely to metastasize. Patients' mean survival time is one to three months without chemotherapy.4 Because these tumors tend to effuse more rapidly, in our experience, palliative pericardiectomy is not usually recommended for hemangiosarcoma because the risk of severe and fatal intrathoracic hemorrhage is significant.
However, in patients with aortic body tumors or mesotheliomas, tumors that effuse more slowly than do hemangiosarcomas, pericardiectomy is often palliative, allowing the fluid to be absorbed through the pleural surface and, thus, preventing the development of cardiac tamponade. Aortic body tumors are located on or surrounding the aortic arch and originate from the chemoreceptors that regulate cardiac function. These tumors are seen more commonly in brachycephalic breeds. They are typically nonresectable but slow growing and unlikely to metastasize.5 If marked pericardial effusion arises with these tumors, pericardiectomy can be palliative. In fact, one study showed that dogs with aortic body tumors treated by pericardiectomy at the time of biopsy had a median survival of 730 days, as compared with 42 days in dogs not treated with pericardiectomy.6 However, in some patients, tumor effusion is minimal and the procedure is never indicated.