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.
For more information, visit http://mysite.verizon.net/jachinitz/hcm or http://www.ncbi.nlm.nih.gov/pubmed/12564730
(Note: Cardiologist Dr. Anthony Tobias referenced in above source article is joining the ACCES specialty team on February 20, 2012.)