Aortic Thromboembolism in Dogs

An aortic thromboembolism is caused by a blood clot, also known as a thrombus, getting lodged in the aorta and blocking blood flow. They often get lodged toward the end of the aorta where it divides into three vessels. This decreases or eliminates the flow of blood to the legs which can cause lameness, pain, and paralysis to the back legs. Although this is a common complication of cardiac disease in cats it is fairly rare in dogs. Prognosis for this disorder is generally poor.

Aortic thromboembolism is caused when a blood clot lodges at the base of the aorta, leading to a reduction or loss of blood flow to a large portion of the body.

Symptoms such as sudden paralysis, respiratory distress, and sudden death are more likely to occur with an acute onset of the disease, whereas the chronic onset aortic thromboembolism presents with the more subtle symptoms such as weakness, limping and lowered body temperature. 

• Absent or diminished femoral pulse
• Anxiety
• Coughing
• Difficulty rising or jumping
• Exercise intolerance
• Hemoptysis (coughing up blood)
• Hypothyroidism
• Limping caused by weakness in hind legs
• Lowered body temperature
• Respiratory distress
• Sudden paralysis and pain
• Toe wounds
• Unusual vocalizations
• Weakness
• Sudden death

Types 

Acute onset

• This is a complete blockage of the blood at the end of the aorta, with symptoms that come on suddenly
• This type of onset is more likely to present with sudden paralysis, pain and respiratory distress than the chronic onset
• Cats usually present with these types of symptoms while dogs are more likely to develop the chronic onset of the disorder 

Chronic onset

• This is either a blood clot that only partially disrupts the flow of blood through the aorta or a blood clot far enough down the aorta that other blood vessels are supplying some blood to the affected area, although the amount is severely diminished
• This is the more common onset to see in dogs affected by aortic thromboembolism

This disorder almost always has an underlying cause that affects the heart, and is more common in male animals than female.

• Bacterial infection (sepsis or septicemia)
• Cancer
• Cardiomyopathy 
• Damage to the lining of a blood vessel
• Enlarged left atrium
• Heartworm
• Hyperadrenocorticism
• Hyperthyroidism
• Iron deficiency
• Platelet abnormalities
• Poorly working heart
• Possible breed predisposition (Greyhound, Soft-coated Wheaten Terrier, Cavalier King Charles Spaniel)
• Protein-losing nephropathy 
• Splenectomy

Your veterinarian will want to start with a verbal history of symptoms and a physical evaluation. During the physical evaluation specific attention will be paid to the sound of the heart and the color of the skin and mucous membranes. When the veterinarian attempts to get a pulse from the hind legs, it will be weakened and possibly erratic. The pulse rate may not match the pulse rate of the other hind leg. A urinalysis, biochemistry profile and a complete blood count will be done to determine what underlying causes may be involved. Ultrasound imaging may be used in order to confirm the presence of the clot. In some situations, an angiography test may be used. An angiography uses a sterile dye is used to show the currents in the blood and to locate areas of decreased or absent blood flow. This test tends to be more invasive than the ultrasound and requires sedation or general anesthesia to complete.

Regardless of the underlying cause, action must be taken against the clot itself. There are several techniques that can be used against the clot itself. Clot-dissolving drug therapy or surgical removal of the clot will be necessary to reestablish blood flow to the affected body parts. The most commonly used clot-dissolving medication for dogs is streptokinase, which is particularly helpful with newly formed clots. The use of streptokinase increases the risk of developing a dangerous condition, reperfusion injury. This condition occurs when toxins build up behind the clot due to lack of oxygen. When the clot is released, the toxins that have been building up such as potassium and acids are released into the body. This has been known to cause shock and even death. The risk of reperfusion injury does seem to be lessened in dogs as opposed to cats. If the clot is not reduced by the medication, then surgery will be done to remove the clot if feasible.

Prognosis is poor for canines with aortic thromboembolism. Many either die of the disorder or are euthanized for humane reasons. The dogs that do recover run a higher than average chance of developing another dangerous blood clot. In an attempt to prevent that from happening, your veterinarian may recommend giving your pet a medication to keep clots from forming. The three most commonly used medications for this purpose are aspirin, warfarin, and heparin. Each of these options has benefits and risks to consider and each will require frequent monitoring of your dog to ensure that coagulation times are appropriate and to make sure the dose is given in the right area.