Idiopathic hemorrhagic pericardial effusion
This clinical entity is second in frequency to neoplasia as a cause of pericardial effusion in dogs, reportedly accounting
for 20% to 75% of cases.7 It is a diagnosis of exclusion that is arrived at after a thorough echocardiographic examination to rule out cardiac neoplasia
and other possible causes of intrapericardial fluid accumulation. This disorder is more common in large- and giant-breed dogs
and is thought to be an inflammatory condition affecting the pericardial sac. One-time pericardiocentesis is curative in about
half of cases.8 If multiple taps are required, pericardiectomy is recommended and is usually curative.
Congestive heart failure
Although congestive heart failure is a common cause of pericardial effusion in cats, it is a less common cause in dogs.9
When congestive heart failure leads to intrapericardial fluid accumulation, cardiac tamponade is rare, and pericardiocentesis
is almost never indicated.10 In some cases, however, modification of congestive heart failure medications may be warranted.
Peritoneopericardial diaphragmatic hernia
Peritoneopericardial diaphragmatic hernia (or peritoneopericardial hernia) is a congenital disorder involving anomalous development
of the diaphragm and pleuropericardial membranes that allows abdominal organ herniation into the pericardial sac in dogs and
cats. These rare lesions can be present for a long period without resulting in clinical signs and are occasionally diagnosed
serendipitously in middle-aged patients that are presented for nonthoracic diseases. In our experience, when necessary, surgical
repair of this disorder is usually successful, although the procedure is technically demanding and often requires specialized
materials, such as Dacron mesh. Adult, asymptomatic animals with a peritoneopericardial hernia require no treatment, but patients
with clinical signs compatible with intestinal or gastric obstruction or vascular compromise must be treated aggressively.11 Pericardial effusion is rarely present with these lesions, and, therefore, clinical signs associated with cardiac tamponade
are not typical.
Left atrial rupture
In some patients with chronic mitral valve disease and severe left atrial enlargement, left atrial tearing is a possible cause
of pericardial effusion. The hemorrhage rapidly leads to cardiac tamponade, cardiogenic shock, and possibly death. The pericardial
effusion may contain a clot because hemorrhage is acute. The clot is often visible on an echocardiogram as a hypoechoic structure
within the fluid-filled (anechoic) pericardial space. Left atrial rupture in association with degenerative mitral valve disease
is apparently more frequent in male poodles, dachshunds, and cocker spaniels.12 However, any dog with severe degenerative mitral valve disease is at risk for this catastrophic sequela.12 Therefore, small-breed dogs with pericardial effusion and systolic cardiac murmurs should be evaluated critically for possible
left atrial tears. Pericardiocentesis in these patients may encourage continued bleeding into the pericardial space. Therefore,
in general, pericardiocentesis is not recommended in these patients. Instead, supportive care with fluid therapy and echocardiographic
monitoring of effusion accumulation are preferred. If the patient destabilizes because of cardiac tamponade, pericardiocentesis
is performed, but the prognosis is guarded at best.