Thursday, February 9, 2012

Feline Saddle Thrombus

By Beth Guerra, DVM
Cats can develop a particular type of heart disease, known as hypertrophic cardiomyopathy (HCM). In this type of cardiomyopathy, the left ventricular wall becomes very thickened, or hypertrophied. This differs from the canine type, which is characterized by a dilated heart with thin walled chambers. These changes can lead to a variety of systemic problems, such as abnormal heart rhythms and murmurs, decreased oxygen delivery to heart muscle, and increased blood pressure. There can also be a change in blood flow through the chambers of the heart. Several of these changes together can lead to the formation of thrombi, or clots, within the heart. These clots are sent through circulation and can become lodged in distant arteries, causing an obstruction of blood flow. One of the most common sites for these clots to end up is where the aorta divides into two major arteries supplying the rear limbs. The presence of a clot, known as a ‘saddle thrombus,' is a strong indication that there is underlying heart disease.
Thrombus formation is acute and often the reason for presentation to the ER. Immediate symptoms include vocalization, discomfort, and paralysis of the rear limbs. Upon examination, no pulses in the limbs can be detected, the rectal temperature may be decreased (<97 F), and the rear paws may be cool to the touch or the nail beds bluish in color. Less often, a thrombus can form in one of the forelimbs, leading to similar symptoms of lameness or cold paw pads. Smaller thrombi can also shower the brain, lungs, or kidneys, leading to neurologic signs, respiratory difficult, or kidney failure. Because the saddle thrombus is nearly impossible to diagnose based on imaging techniques such as x-ray, diagnosis is usually made based on physical examination. A history of heart disease, murmur at time of exam, or arrhythmias/hypertension can also help solidify the diagnosis of HCM.
Treatment is multifactorial, as both the thrombus and the underlying heart disease must be addressed. An echocardiogram (ultrasound) of the heart is the best way to confirm HCM. This disease in cats is not reversible; treatment is aimed at trying to prevent further thrombi from forming and can include heparin initially and then aspirin or Plavix. Other drugs may be added based on the severity of heart failure. However, there is no foolproof way to break down the pre-existing saddle thrombus with medications, although it may break up on its own over time. Supportive treatment is indicated during the initial days, and is aimed at nutritional support, pain control, and physical therapy. If circulation cannot be restored within one to two days, necrosis of the limbs can develop, ending in either partial amputation or euthanasia. Although prognosis is generally guarded, it is reasonable to support the cat for a few days with pain medications to see if circulation returns to the limbs. Survival can be up to 10 to 12 months after diagnosis, however, these cats are usually euthanized if the initial clot fails to resolve or if symptoms recur, eve n if the cat is on medication.

(Note: Cardiologist Dr. Anthony Tobias referenced in above source article is joining the ACCES specialty team on February 20, 2012.)

Thursday, February 2, 2012

The Subtle Signs of Pericardial Effusion

By Dr. Beth Guerra

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.