“Minty” was a lovely Black and White striped cat. He was rushed in and admitted urgently as an emergency case to the main surgery. He was in shock and in severe pain, and he couldn’t stand up on either of his hindlegs. He was admitted for immediate pain relief and tests which revealed that “Minty” had a saddle thromboembolism, blocking the blood supply to his back legs.
“Saddle thromboembolism” is a life-threatening condition that occurs when a blood clot, or embolus, breaks away from a larger clot, a thrombus, within the heart and travels down the aorta. This embolus then lodges itself at the junction of the iliac arteries of the hind legs, at the bifurcation of the aorta blocking blood flow to one or both patients’ hind limbs. The term “saddle” thromboembolism is due to the embolus lodging in the junction of the arteries and draping down into the vessels, giving it the appearance of a “saddle”. In some cases, if the clot is small, it may travel past this junction and lodge in a smaller back-leg artery. In this case, symptoms can appear in just one leg. Blood clots can also travel to other parts of the body, blocking blood flow to organs such as the kidneys, lungs, or brain.
The most common underlying cause of a saddle thrombus is a known, or an undiagnosed, underlying heart disease, typically “hypertrophic cardiomyopathy”, where chamber enlargement and wall thickening within the heart predisposes the patient to turbulence and blood pooling, and so to the formation of blood clots. Studies show that between 69-90% of cats with thromboembolism have an underlying heart disease and up to a third of cats with heart disease may develop a blocked artery due to thromboembolism. Saddle thrombosis can develop in cats of any age or breed; one study found the mean age was 12 years. Other causes include neoplasia and hyperthyroidism.
Saddle thromboembolism is a distressing and devastating condition, as often there is little or no warning. At any time, a clot formed in the heart can then dislodge and travel along the aorta before becoming wedged in the narrower iliac arteries supplying the hindlimbs.
The symptoms are: Sudden and acute, severe pain, with distressed howling and vocalisation noted; Frantic licking or chewing at the affected legs; Paralysis or weakness of the hind limbs, being unable to stand or dragging one or both back legs; Firm, painful hindlimb muscles; Loss of a pulse in the affected limbs; Cold hindlimbs; Blueish tinged skin and pads noted on the affected limbs; and Pale gums, as these patients are in severe shock.
Once blocked, blood can no longer pass into the iliac arteries, which means the tissues in the hindlegs are no longer receiving adequate oxygen, a cascade of biochemical reactions within the cells follows, leading to toxic by-products which ultimately cause cell death. These harmful toxic by-products which have built up are released back into the circulatory system.
Aortic thromboembolism is a critical medical emergency and requires immediate veterinary attention.
After admission if an aortic thromboembolism is suspected strong painkillers are administered quickly as this is an excruciatingly painful condition. Emergency treatment involves an immediate safe sedation and adequate, tailored pain relief for these distressed, painful cases.
Blood tests will reveal any blood abnormalities, and an ultrasound scan an abdominal doppler ultrasound may reveal the embolism and visualise the lack of blood flow. A cardiac scan may reveal cardiac abnormalities and a large thrombus within the heart.
On-going strong pain relief and safe sedation is required along with carefully monitored intravenous fluids to correct the toxic electrolyte and biochemical derangements caused by the embolism, and thrombolytics are also given to attempt to dissolve the clot.
Abnormal cardiac sounds are a common finding, as these cats often do have an underlying heart disease which also needs to be stabilised. Anticoagulant therapy such as heparin or aspirin are also given to thin the blood and help stop additional blood clots from forming.
These are really distressing cases, and sadly, many cats don’t survive a saddle thromboembolism and treatment in these cases is very often unsuccessful. The required blood thinners and thrombolytics run the risk of causing other bleeding complications. Often the underlying problem is a thrombus within the heart which splits off further emboli, and so any invasive surgery is usually not advised, or possible. Even if the cat recovers from the initial event, the risk of another clot forming is then extremely high. On top of that there is usually an underlying severe heart condition causing the thrombus to form in the first place. Many owners elect to euthanise cats with aortic thromboembolism due to the severe shock and pain that they go through, and the poor outcome and prognosis for these cases.
“Minty” was thirteen years old, and it was found during his tests that he also had a severe, underlying cardiac condition with a thrombus also noted within his heart. After hearing this, his owners then decided that it was kinder to give him a gentle release from this condition, rather than risk him having further clots forming and go through this trauma again. “Minty” was quietly put to rest.
It was so upsetting and very sad; however, his owners were relieved that he would not go through any further pain and suffering now, and they remembered all the many happy years that they had had with him.
Alison Laurie-Chalmers,
Senior Consultant,
Crown Vets