Occasionally, as a veterinarian I must chase down a diagnosis with not much to go on. An animal presents with very vague symptoms but both the owner and I know that something is amiss. Through experience, I have learned to think outside the box in some situations and look for the ‘zebra’ diagnosis when symptoms just don’t add up.
One of these elusive diagnoses is pericardial effusion. The heart is contained within a mostly rigid sac, called the pericardium. When fluid or blood accumulates in this space, the heart is compressed and cannot expand efficiently. Because of this, blood flow through the heart is decreased, leading to compromised peripheral circulation. To compensate, the heart beats faster to try and make up for the deficit. This compression of the heart by fluid is known as cardiac tamponade. Blood pressure drops, oxygenation is low, and the animal may experience collapsing episodes. Sometimes they have pale mucus membranes, or muffled heart sounds from the fluid that has built up. Diagnosis is based on x-ray, where a large, globoid heart silhouette is seen, or more easily with ultrasound, where fluid around the heart is directly visualized. Sometimes the ECG will show characteristic changes in the tracing.
In a textbook situation, all of the above symptoms occur. More often, I have animals that present with subtle symptoms, such as slow, deep breathing, mild weakness when walking, or apparent abdominal pain (hunched posture, groaning). Physical exam reveals none of the classic symptoms of pericardial effusion. The history is inconclusive. Yet something tells me to look for the ‘zebra’, to systematically evaluate every body system to try and explain the symptoms. Since I have access to a portable ultrasound, in these cases I will often do a quick scan of the heart to see if there is any pericardial fluid. It is a relief when I find it, because I have a diagnosis. However, the presence of this fluid usually indicates a poor prognosis.
Fairly frequently, animals with pericardial effusion are in distress. The quickest way to stabilize such a patient is to remove the fluid with a needle, known as pericardiocentesis. This also allows the doctor to examine the fluid to try and determine an underlying cause. The fluid is often blood, which can indicate a heart base tumor that has ruptured. Occasionally, the fluid is clear or has very little blood, which may also indicate a tumor but may also be idiopathic (unknown cause). Diagnosing tumors in this area can be extremely difficult, as they can be too small to detect on thoracic ultrasound. A CT may be recommended, especially if surgical intervention is being considered. Some owners choose to treat palliatively, draining the fluid as needed, although this does present its own risks. If a tumor is found, the overall long term prognosis is poor. In the rare instance of idiopathic effusion, some animals may do well with a surgery to remove the heart sac.
ACCES is lucky to have a veterinary cardiologist joining our staff to help with these difficult cases. Anthony Tobias, DVM DACVIM (Cardiology) will be joining ACCES February 20, 2012.