Saddle thrombus: blood clots, heart disease, and your cat

Patty Khuly, DVM
Updated: January 22, 2021
Published: November 23, 2009
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Picture this: You wake up groggily one Saturday morning — admittedly a bit on the late side — and you suddenly realize that your ten year-old kitty companion is nowhere to be seen. She’s typically right there, meowling and staring at you plaintively so you’ll get up and fill her food bowl.

You look everywhere and finally you find her in her 'strange-people-are-here' hiding spot under the sink in the bathroom. She’s panting and doesn't get up to greet you. Immediately, you become alarmed when you reach in to lift her from her little cave and she lets out a strange and horrible cry you’ve never heard from her before.

Panicked, you throw on some clothes, wrap her in a towel and drive the five miles from your home to the vet's in record time, ignoring the stop signs and red lights wherever you can.

Inside the vet's clinic the waiting room is packed. The receptionist calmly asks you if you have an appointment.

“No, it’s an emergency,” you answer impatiently. “She’s breathing strangely and she can’t move. I think she’s in a lot of pain. She might have broken her back.”

Near hysteria at this point, you ask to see the vet “NOW!” Luckily, she’s heard the commotion and it takes her no time to assess your kitty’s state. She whisks you back into the only unoccupied room on this busy Saturday for an x-ray.

She performs what seems like the fastest physical exam in the world before announcing she’ll be right back with a dose of hydromorphone, the strongest pain reliever she’s got. A technician is already placing an IV catheter. Another is taking her temperature and preparing the x-ray machine. Meanwhile, Kitty’s eyes are wide with panic. You pray the vet returns quickly.

She administers the dose, and less than half a minute later Kitty relaxes. But it’s not enough. A more cautious physical exam reveals that more pain medication is in order. Another dose. Now Kitty looks near-catatonic. Your vet reassures you that the second dose was necessary before taking x-rays. She then launches into what seems to you a too-calm explanation of your cat’s problem:

"She’s almost certainly suffering from a saddle thrombus," she begins. "A thrombus is a clot that forms in the bloodstream, in this case usually in the heart. When it’s dislodged from the heart and enters the aorta it ends up lodging itself at the bifurcation of this large artery as it branches off into the smaller arteries that supply blood to the hind limbs. When it gets stuck it’s now called an embolism, and the result in the case of a saddle thrombus (an embolism at the base of the aorta) is that it cuts off the main blood supply to the back legs; an extremely painful condition."

“See how her back legs are cold?” says your vet. You touch them and confirm that they’re definitely colder than her front legs.

“So her back’s not broken?” you ask hopefully. Your vet now shows you the x-rays and it's true, no break. Just a larger than normal heart and some fluid in the chest. She explains that Kitty has congestive heart failure along with serious heart disease and this latter issue is what precipitated the formation of the clot. "Nearly 90% of saddle thrombus cases have underlying heart disease," she adds.

The congestive failure (the inability of her heart to pump the blood effectively, thereby allowing fluid to accumulate in her lungs) came later, probably as a result of the serious stress she was suffering.

You stare blankly at her and say, “But she was just here three months ago. How could you not know she had heart disease?”

Sheepishly, your vet explains that some heart conditions do not make themselves known through standard physical examination and laboratory testing.

“Performing a cardiac ultrasound is sometimes the only way we can determine this. EKGs are often inconclusive in these cases, though that may have helped,” she concedes. “But it’s just not yet part of our standard screening for cats. Not when everything else checks out fine."

“Our job now is to decide how we treat this. Why don’t we focus on that for the moment?” she urges.

That’s when she gives you two choices:

1) Immediate intensive care at the specialty hospital, where they’ll place your Kitty in an oxygen cage and supply drugs to support the heart and treat the congestive failure, and administer blood thinners to help dissolve the clot.

Surgery can sometimes be effective when the clot is caught very early on. In this case surgery’s not likely an option due to her congestive heart failure and the fact that this happened sometime overnight.

There will be more x-rays, more labwork and an ultrasound of her chest. In 35-40% of treated cases, cats will recover well enough from the damage done to their nerves (a result of the poor blood supply) to be able to use their hind legs again. Because of her congestive heart failure, however, her chances are slimmer than that. She may well die during treatment.

2) The only other choice: euthanasia.

You may say, “That’s it? I have no other choices? Can’t I give her medications and treat her at home?”

At least she can die in peace in familiar surroundings, you reason.

“Or perhaps you could treat her here?”

But your vet is firm on this.

“There’s no way to manage her severe pain,” she explains. “You have to be willing to choose one path or the other. There’s no middle ground here. And, it’s Saturday," she adds. "We have no 24-hour care. This is a serious condition I could treat with halfway measures to some effect, but I’d be doing Kitty a huge disservice. Even if I could get her well again the pain relief she requires means continuous monitoring." 

Your vet gives you several seconds to digest this and then gently adds, "I know you don’t want her to suffer so I’m giving it to you straight. You have no other choices."

In the end you drive Kitty to the specialty hospital where she dies overnight in spite of the internal medicine specialist’s best efforts. A complication of her kidneys and her heart failure combined, you’re told, since lab tests revealed that her kidneys also received a clot.


I know it’s not a happy story, but that’s what happened here one recent weekend over a 24 hour period. Kitty’s condition might have been prevented through judicious use of aspirin on a regular basis, but we had no inkling of her underlying heart disease. No murmur. No exercise intolerance (hard to assess in a cat, in any case). Nothing. There were also no x-rays, EKGs or cardiac ultrasounds done before the fact, but there was no reason to think we needed them.

Though all my feline heart murmur cases used to get treated to a tiny dose of aspirin every other day, it's not been proven to work, so I no longer go that way. Instead, I offer most of my clients the cardiac workup so we can at least determine whether we're at a high risk for a saddle thrombus. Though my clients often opt out of this expensive approach, they are at least offered the choice. Beyond this approach there's not much we can do in advance of the problem. Hopefully, things will change with the results of some new studies, but until then, owners will just have to be aware of what to look for.  

Dr. Patty Khuly