Most of the time when I’m writing these I’m thinking of diseases, conditions or situations where we can really make a positive difference or there is some way to prevent or manage the problem. This week is about one of those terrible situations for which there is really little we can do and little warning about what may be happening. Fortunately they are not terribly common. Statistics, however, do little to console those few owners who have something like this happen to a beloved family pet.
When cats develop heart disease they tend to do it a little differently than dogs. They will overgrow or thicken their ventricle walls, the ventricle is the part of the heart that pushes the blood into the aorta or pulmonary vein and move it into the circulation. If the ventricle wall becomes thicker the ventricle will have difficulty relaxing and filling with blood. The ventricle also has difficulty filling because the space is smaller. This can lead to sudden decreases in cardiac output that occur at times when the cat needs the blood the most (during dog chases for example) and this can lead to sudden death. Blood needs to flow in a specific pattern through the body. It flows in layers and we call this a lamellar flow pattern. If these layers are disturbed during flow by a heart murmur or pushing the blood through a narrowed space the factors that affect clotting can be activated and a clot can form. This clot is pushed out into the aorta and a moving clot in the blood stream is called an embolus. Technically, it is called a thromboembolus as it is made of a blood clot (thrombo = blood clot).
The embolus will move down the bloodstream until it encounters a vessel too small for it to pass through. There it will lodge and occlude blood flow. In cats, this typically occurs at the end of the aorta where the major vessel splits into the supporting arteries of the pelvic limbs. (These are the iliac arteries, this will be important in a minute.) This blockage is very painful, sudden and often causes a complete loss of blood flow to the affected limb or both limbs. These cats instantly lose their ability to walk, vocalize with pain and will have cold to the touch feet that do not respond to stimulus.
Treatment for a thromboembolism is available but it is very expensive, there are cases where cats do die during administration of the drugs involved and there is a very high recurrence rate of thromboembolisms in cats with heart disease. As a result, many people do not go for clot lysing treatment. Most commonly we will manage these cats with supportive care for 72 hours. During that time we try to facilitate clot breakdown, manage the cat’s pain and dilate the vessels a little bit. If we can get the clot to move down the iliac arteries there is collateral circulation, the deep circumferential iliac and theinternal iliac vessels branch from the external iliac which is the major large vessel in the pelvic limb. If we can open flow to these vessels the collateral circulation can start to feed the muscles and we can prevent serious, irreversible damage. This may buy us enough time for the body to break down the rest of the clot and over time the cat may regain its ability to walk.
There is approximately a 50% chance that the cat will recover with supportive care. After that there is a very good chance that it will happen again in the next few months or even weeks. For this reason, many of these cats are euthanized when they throw clots rather than treated. If we are successful and the cat doesn’t throw a clot in the following months we recommend a complete cardiac examination including echocardiography to evaluate for heart failure. Cats with hypertrophic cardiomyopathy, the most common heart disease in cats, with evidence of heart failure will typically succumb to well treated heart disease 12 to 18 months after the diagnosis. If there is not evidence of heart failure our course of treatment involves lowering the heart rate and relaxing the heart muscle. We will also start a clot preventing therapy using aspirin or sometimes plavix. While these treatments work anecdotally, there is little clinically supported evidence for thier use.
While we all have a few really good success stories to drag out and show off regarding thromboembolisms in cats, ultimately the realistic expectation we should be giving owners is that this probably isn’t going to get better. These cats can have their pain managed for a few days and we can give them a chance, if the owners want to try break down the clot and treat the heart disease I am all for it. In cases like this, however, it is very important to me that we all go in with both eyes open and understanding that even our best efforts may not be enough to overcome the disease we are dealing with.
The one area where prevention might be possible is if you have a breed of cat predisposed to heart disease or if your veterinarian has heard a murmur, it might be useful to have an echocardiogram performed and if there are signs of heart disease, putting your cat on anticoagulant medication can help prevent the formation of thromboembolisms. They also prevent the normal clotting that keeps us from bleeding excessively from small wounds so treatment/prevention is not without risk.
Thanks for reading.