Although not always necessary to diagnose cardiac tamponade, echocardiography is the most useful tool for diagnosing the underlying
pericardial disease and may be the only way to detect small volumes of pericardial effusion.21 A thorough echocardiogram allows rapid confirmation of the presence of pericardial effusion (Figure 5); identify intrapericardial masses (Figure 6), including blood clots; observe evidence of left atrial rupture; assess the thickness of the pericardium; evaluate cardiac
tamponade; and confirm the presence or absence of pleural effusion. The presence of bowel loops, stomach, or other abdominal
organs in the pericardial sac confirms a diagnosis of peritoneopericardial diaphragmatic hernia. Abdominal ultrasonography
of older dogs with pericardial effusion is useful in identifying splenic or liver neoplasia. Hepatic vein distention and ascites
support the presence of increased systemic venous pressure, though this finding is not restricted to patients with cardiac
5. A short-axis echocardiogram obtained from the right parasternal window in a dog. Note the pericardial effusion (anechoic
area) surrounding the heart (RV=right ventricle; LV=left ventricle; PE=pericardial effusion).
Pericardial fluid analysis
Pericardiocentesis is vital for therapeutic purposes if tamponade is present, and it also can be useful to collect samples
for diagnostic testing. Collect samples in EDTA tubes and plain tubes for submission to a laboratory for cytologic examination
and bacterial culture and antimicrobial sensitivity testing if indicated. Diagnosis of a neoplastic process is difficult because
reactive mesothelial cells are often present in effusions even when the underlying process is benign. However, cytologic examination
is occasionally helpful, particularly if an inflammatory process is likely. Fluid pH was once reported to help distinguish
between neoplastic and idiopathic effusions, but a recent study has shown that the overlap between the two groups is too great
to be of diagnostic utility.22
6. A right parasternal echocardiogram obtained at the heart base in a dog. Note the hypoechoic mass (arrow) on the right atrial
appendage that is the presumptive cause of the effusion. The mass was a hemangiosarcoma.
Treatment of pericardial disease is aimed at correcting the underlying disorder or attempting to minimize its impact on cardiac
function. When cardiac tamponade is present, emergent removal of pericardial fluid is indicated. Reduction in pericardial
pressure after fluid removal leads to an immediate increase in cardiac output, a decrease in heart rate, and a marked improvement
in the patient's clinical status. Large volume ascites that develops secondary to cardiac tamponade can be removed if the
patient is experiencing ventilatory compromise or discomfort.23 However, in most cases, once cardiac tamponade is relieved, ascites will resolve rapidly because of diuresis. Diuretic medications
are also not necessary. In general, long-term management and therapy are typically focused on the subset of patients with
recurrent pericardial effusion. If initial therapy is ineffective or if the effusion becomes recurrent, more definitive procedures,
such as pericardiectomy, are recommended.
For a discussion on pericardiocentesis, including a step-by-step description of the procedure, see "How to perform a pericardiocentesis".
A complete discussion of pericardiectomy procedures is beyond the scope of this article. Although historically performed via
thoracotomy, many of these procedures are now performed via thoracoscopy and involve either making a window in the pericardium
or removing most of the pericardium (subtotal pericardiectomy).1 Other minimally invasive procedures (e.g. balloon pericardial windows) have proven successful.1 For chronic diseases such as idiopathic hemorrhagic pericardial effusion, any fluid that would have accumulated in the pericardial
sac is simply reabsorbed via the mediastinal vasculature and lymphatics.