Many of us have had cuts and scrapes. These stop bleeding because of our blood's ability to clot. Cats (and very rarely, dogs) with heart disease are at an increased risk of developing an
aortic thromboembolism (ATE). Commonly, a cat with heart disease will form a large clot (called a thrombus) that is almost always found in a chamber of the heart known as the left atrium. In heart disease, this chamber of the heart tends to enlarge, which has been shown to increase the chance of thrombus formation there.
These clots are very dangerous. Pieces of them (or the whole thrombus) can break off and be pumped out of the heart and into the arteries. The thrombus can eventually get trapped in smaller arteries, clogging them and preventing blood from flowing past. This most often occurs right before the largest artery in the body (known as the aorta) branches to deliver blood to the rear limbs. Consequently, the cat's hind limbs will became extremely painful and paralyzed. The legs will feel cold and the foot pads may become a pale gray or blue color. Less commonly, the thrombus can block blood flow to a front limb, the kidneys, brain, lungs or the heart itself. Without blood, these vital organs cannot function.
There are several different treatment options for a pet with a thromboembolism. The most appropriate one will depend on the size of the thrombus, how long it has blocked blood flow, the severity of symptoms the cat has and any other underlying medical conditions. Medicines called thrombolytics (such as streptokinase and tPA) may be used to break down the thrombus, however these can be dangerous and can cause bleeding. The thrombus may also be physically broken up surgically or via a catheter (called a catheter thrombolectomy).
Once arterial thromboembolism has developed it is very hard to treat, so the most common approach is to prevent them from ever occurring. A cat with heart disease (and an enlarged left atrium) may be placed on a small dose of aspirin which acts on platelets to prevent clots from forming. Another antiplatelet drug called clopidogrel (Plavix®) may also be used. Low molecular weight heparins such as dalteparin (Fragmin®) and enoxaparin (Lovenox®) belong to a class of medications known as blood thinners or anticoagulants. They can also be used to prevent blood clots from forming.