Saddle Thrombus
What is saddle thrombus?
A condition that affects cats that can occur very suddenly without any prior signs or symptoms. It occurs when a blood clot
(called a thrombus) forms or lodges at the point where the main artery leaving the heart (the aorta) divides into the arteries
supplying blood to the hind legs (the iliac arteries) and the vessel supplying the tail.
Tell me more
The aorta is the widest artery in the body,
and when it splits at this trifurcation, the
iliac arteries are significantly smaller.
The thrombus (clot) normally forms in the
heart and travels down the aorta without
causing problems.
When it reaches the iliac arteries it gets
stuck occluding the blood flow and this
means the legs no longer have a blood
Vital supplies of blood and oxygen are
abruptly halted, with no backup (collateral
Why does this happen?
Any heart disease that causes abnormal turbulence can
cause a thrombus to form in the left atrium.
The most common cause is Hypertrophic Cardiomyopathy
(HCM) which is a condition where the heart muscle becomes
thickened making it harder for the heart to pump.
Cardiomyopathy literally means heart muscle disease.
Other causes:
Restrictive Cardiomyopathy (RCM), scarring of the heart prevents normal pumping
Dilated Cardiomyopathy (DCM), the walls of the heart balloon out causing an
enlarged, weak walled heart.
Mitral Valve Disease, the mitral valve controls the flow of blood on the left side of
the heart, if it wears out blood flows backwards back into the left atrium.
Heart Based Tumors
What will I see? Symptoms
Howling, crying or screaming. A thrombus
is extremely painful.
Hiding and not wanting to be touched or
Open mouth panting
Inability to walk, dragging one or both hind
Cold legs and feet. Toes may be pale or
What will the vet do?
The vet will be suspicious based on the
history and clinical signs.
Ultrasound of the iliac arteries may show the
In 76% of cats with saddle thrombus, this
was the first sign of heart disease.
Chest x-rays will look for heart failure – this
shows up as fluid in or around the lungs.
Blood testing will assess general health and
ability to tolerate medications.
Echocardiography to classify the heart
Begin treatment of the underlying heart
disease when the patient is stable.
Pain management!
Intravenous heparin to attempt to dissolve
the clot.
Aspirin or Plavix ®
Physical therapy
Oxygen therapy as needed.
Intravenous fluid therapy.
Surgical intervention is associated with a
poor survival rate.
Treatment Part 2 – More Detail
The patient’s clotting factors and platelet count
should be done before initiating heparin therapy.
Low molecular weight heparin (LMWH) is the drug
of choice for treatment.
Aspirin and Plavix © are also used because they
have anti-platelet activity.
Streptokinase and urokinase are used in people to
improve arterial blood flow. Few studies have
been done in cats. In one study all the cats died
after receiving streptokinase.
t-pa or tissue plasma activator is also used in
human thrombolytic therapy. This drug is very
expensive and also hasn’t been widely tested in
Supportive Care
Nursing care involves managing the comfort of the
affected limbs.
The legs need to be kept warm.
Physical therapy including passive range of
motion. The care giver moves a joint through its
entire range of motion without assistance from the
Bladder support. The patient may not be able to
urinate on his own and may need to have his
bladder expressed.
Drug Therapies for Preventing Recurrence
The anti-platelet drugs:
◦ Aspirin has been in use for more than 30 years in
treatment of thromboembolism. It works indirectly
and has only moderate anti-platelet activity.
◦ Plavix or clopidogrel affects platelets directly and is
thought to prevent recurrence of arterial
The anti-coagulant drugs:
◦ Warfarin interferes with Vitamin K and disrupts the
clotting cascade. Warfarin should be used in
conjunction with heparin. Warfarin can be
challenging even a minor injury could cause a life
threatening hemorrhage.
◦ Low molecular weight heparin (LMWH) is used in clot
prevention. The most common side effect is minor
What is the prognosis?
Unfortunately the prognosis is very poor.
Even if treated successfully the likelihood
of another clot forming is high.
Cats with a rectal temperature of 98.9F
have a 50% or higher chance of survival.
25% of pet owners elect euthanasia
without attempting treatment.
Median survival time of cats in heart failure
is 77 days. Cats not in heart failure 223
Home Care: What to Expect
It may take 3 weeks or more for the cat to regain hind
limb function. Full function may never return. Care is
similar to that of a paralyzed pet.
Urinary and fecal incontinence is not uncommon. He
will also have limited ability to groom himself.
Frequent baths are a must to prevent urine and fecal
Underpads manufactured as a human incontinence aid
are incredibly helpful in maintaining a clean
Be aware of the potential for pressure sores from
sitting in one position for long periods of time, and
scrapes from dragging the hind limbs around.
His bladder may or many not need to be expressed to
allow him to urinate.
Continued physical therapy at home will help keep the
limbs flexible.
There is no known way to predict which atrisk cat will develop a embolism.
The best prevention is regular veterinary
If there are any signs of heart disease:
◦ Heart murmur
◦ Change in rhythm
◦ Change in breathing patterns
They should be followed up on:
◦ Blood tests
◦ Echocardiogram (ultrasound of the heart)
◦ Referral to a cardiologist (heart specialist)
CVCA Cardiac Care for Pets (2013). Echocardiogram [Ultrasound Image]. Retrieved from
Drs. Foster & Smith Educational Staff (n.d.). Saddle Thrombi Diagram [Line Drawing]. Retrieved from
The Merck Manual For Pet Health (2011). Thrombus [Line Drawing]. Retrieved from:
Nelson, R. W., & Couto, C. G. (2003). Aortic thromboembolism in a cat [Photograph]. Retrieved from
Pavlina, S. (2013). Feline arterial thromboembolism: A terrible FATE. Veterinary Technician, E1-4. Retrieved from
Ware, W.A. (n.d). Hypertrophic Cardiomyopathy [Drawing]. Retrieved from