Cardiac tamponade is a condition in which excessive fluid develops in the sac that surrounds the heart which results in failure of the heart to pump blood adequately.

The primary clinical signs of cardiac tamponade is weakness.

Treatment involves removing fluid from the sac around the heart .

Prognosis is highly dependant on the underlying cause.

What is pericardial effusion?

• The pericardium is a thin membrane that follows the contour of the heart and forms a sac-like structure.  Most of the time, the sac is empty and the membrane serves as a lubricated surface inside which the heart can move easily.  When fluid collects within that sac, we call the fluid pericardial effusion.  If enough fluid collects within the sac over a short period of time, it can cause a condition called cardiac tamponade.  During cardiac tamponade the fluid puts pressure on the heart to the point that the chambers of the heart cannot expand to fill with blood.  If they cannot fill with blood, the heart cannot pump blood to the rest of the body.
  
• Fluid can collect in the pericardium for a number of reasons including:  bleeding, bacterial or viral infection, heart failure, low blood protein (albumin) levels, leaking of fluid associated with a tumor, or other ill-defined causes.
  

Clinical Signs

• What you notice at home can be very general signs of illness:  weakness, lethargy, intolerance to exercise, and decreased appetite.  If your pet’s appetite has been decreased for a long time, weight loss may be noticeable as well.  In some specific cases, including patients in cardiac tamponade, you may also notice fainting episodes, distention of the belly, or difficulty breathing.
• When your veterinarian listens to the heart, they may describe it as sounding muffled or quieter than usual or that they hear a murmur or abnormal rhythm. 
• Patients experiencing cardiac tamponade may have a change in the feel of their pulses, enlargement of their liver, or development of fluid in the belly. 

Diagnosis

• Using an ultrasound machine, your veterinarian may be able to see the build up of fluid in the pericardium or see the walls of the heart moving abnormally. 
• An abnormal rhythm may be visible on an ECG, the method used to see the electrical activity of the heart. 
• X-rays of the chest may show a very large, round heart as well as enlargement of the veins returning blood from the lungs to the heart.  Your veterinarian may choose to perform bloodwork including a complete blood count (CBC), serum chemistry profile, and urinalysis to look for signs of underlying disease processes.
  
• If your veterinarian diagnoses pericardial effusion or cardiac tamponade, they will most likely want to remove some of the fluid from the pericardium.  This process is called pericardiocentesis and can be performed in an awake patient or one with mild sedation.  Although the information does not always give a diagnosis, the fluid sample should be cultured and fully evaluated by a pathologist to attempt to determine its origin:  infection, tumor, etc. 

Treatment

• In a patient experiencing cardiac tamponade, by removing even a small amount of fluid, the pressure around the heart is relieved and the patient usually feels much better.  The heart rate decreases and the character of the pulse improves.  Complications associated with this treatment can include puncture or laceration of the heart, lung or major blood vessels, introduction of air, infection or cancer to the remainder of the chest.  The benefits gained from performing pericardiocentesis usually outweigh the potential complictations.
  
• The fluid that was present around the heart may return over a period of days to months.  If pericardiocentesis needs to be repeated, removal of a portion of the pericardium is recommended.  This procedure is done surgically and allows the fluid that would be trapped within the pericardium to drain into the larger space of the chest cavity to then be absorbed.  Removal of a portion of the pericardium can offer a good prognosis depending on the original cause of the pericardial effusion.  Therefore, further diagnostic testing should be performed to determine the underlying cause.  This testing can include, but is not limited to:  chest x-rays, abdmominal ultrasound, echocardiography (ultrasound of the heart), full bloodwork and urinalysis.  Specific treatment for the underlying cause will be determined by your veterinarian after these test results are available.
  
• If your pet has been treated for pericardial effusion or cardiac tamponade, you should be aware of the clinical signs of the fluid returning and monitor your pet for them daily.  As listed above, these clinical signs can include:  weakness, intolerance to exercise, difficulty breathing, decreased appetite, weight loss, fainting, and most importantly, whatever the most noticeable sign was that caused you to have him/her examined by a veterinarian when the condition was first diagnosed.

References

• Textbook of Veterinary Internal Medicine:  Fifth Edition. Editors:  Ettinger, Stephen J., DVM, and Edward C. Feldman, DVM.  Philadelphia, PA:  W.B. Saunders Company, 2000.