Saddle Thrombus: Every Cat Owner's Worst Nightmare

By Patty Khuly, DVM on May 16, 2010

You wake up groggily one Saturday morning — admittedly a bit on the late side — and you suddenly realize how it is you managed to sleep in. 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-guests-are-here hiding spot under the sink in the spare bathroom. Coming closer, you become alarmed. She’s panting and won’t get up to greet you. When you reach in to lift her from her little self-styled cave she lets out a strange and horrible cry you’ve never heard before. Her back legs don't seem to work.

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 speed traps and red lights wherever you deem it's safe enough to get away with it.

Inside the vet's the waiting room is packed. The receptionist calmly asks 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 hysterical by this point, you demand 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: 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. The 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.

After she administers the dose, 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 she looks near-catatonic. Your vet reassures you that the second dose was necessary before taking X-rays––which no longer seem so necessary. She then launches into what seems a way-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 burying into 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. The result in the case of a saddle thrombus (an embolism at the base of the aorta) is that it cuts off the blood supply––mostly to the back legs, which is an extremely painful condition.

Forget broken bones and fractured teeth. This is the stuff of nightmares. Which is why pain releif is always the first order of business whenever we suspect a saddle thrombus.

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

“So her back’s not broken?” Your vet now shows you the X-rays: It's nothing like that. 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. 90% of saddle thrombus cases have underlying heart disease.

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. “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 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 conceded. “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 a couple of choices:

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

Here she’ll receive more imaging (a cardiac ultrasound and perhaps a CT scan) and more labwork. In 35-40% of treated cases (typically if they're treated early on), cats will recover well enough from the damage done to their nerves (a result of the poor blood supply) 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.

Surgery can sometimes be effective when 1) we catch these cases very early on (within hours), 2) when there's not another clot within the patient's heart potentially waiting to imminently dislodge itself, and 3) when the cat isn't in congestive heart failure. In this case surgery’s not likely an option due to her congestive heart failure and the fact that this happened sometime overnight. But it may still be worth a shot. It all depends on the facility's capabilities and your surgeon's aggressive tendencies.

And…

2) Euthanasia.

“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 responsibly manage her severe pain without electing for definitive treatment,” she offers. “You have to be willing to choose one path or the other. There’s no middle ground here. It’s Saturday," she goes on to explain. "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. 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 her 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, you’re told, since lab tests revealed her kidneys also received a clot.

***

I know it’s not a happy story but that’s what happens. We used to think Kitty’s condition could have been prevented through judicious use of aspirin on a regular basis. But even if we did know of her underlying heart disease, we now understand that the effectiveness of preventative drug therapy is no sure thing. We just don't know what works and what doesn't. (Aspirin doesn't seem to make any difference.)

Though all my feline heart murmur cases get offreed a cardiologist's consultation, most of my clients don’t opt for this kind of workup. It's too expensive, they say. But at least they're given the choice. Owners of cats with no symptoms, however, typically don’t get offered an EKG or an X-ray. No doubt you’ll think my protocols lacking. Indeed, I do too. But if my symptomatic patients' owners almost always decline, can you blame me if I don't try and talk every cat owner into a $300-$500 procedure?