What is Caval Syndrome?
Heartworms are parasites that can live 5 to 7 years in their hosts, generally in the arteries of the lungs. This puts pressure on the pulmonary arteries and the right side of the heart. If heartworms invade the vena cava, the vein that delivers venous blood to the heart from the lower body, or the heart itself, it can result in many dangerous conditions that affect other organs, such as the liver and kidneys. This is why it is sometimes called liver failure syndrome.
Caval syndrome is a progressed condition of heartworm disease. When the heartworm parasite has become too populous in the pulmonary artery of an infected dog, they can migrate into the vena cava, right atrium, and right ventricle of the heart. This is a life threatening condition that causes issues ranging from jaundice and anemia to liver dysfunction, heart failure, and death.
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Symptoms of Caval Syndrome in Dogs
Symptoms of caval syndrome are often not present in many dogs with the condition. Though caused by the heartworm parasite, symptoms of caval syndrome are different than those of a typical heartworm infestation, and can include:
- Decrease in activity
- Increased breathing rate, or tachypnea
- Breathing distress
- Fainting when stressed
- Weight loss
- Loss of appetite
- Pale mucous membranes
- Weak pulse
- Blood in the urine
- High level of hemoglobin in the urine, or hemoglobinuria
- Hepatosplenomegaly, or swelling of the liver and spleen
- Irregular gallop or murmur in heartbeat
- Pulmonary hypertension, or high blood pressure in the lungs
- Heart failure
Caval syndrome is a progression of heartworm disease. Symptoms of heartworm disease can be seen most often following exercise, and can include:
- Soft, dry cough
- Shortness of breath
- Decreased stamina
- Fainting spells
Causes of Caval Syndrome in Dogs
The one and only cause of caval syndrome is:
- Heartworms that migrate into the vena cava and heart
The heartworm parasite is spread from animal to animal through a bite from an infected mosquito. Caval syndrome is most common in male dogs showing no previous signs of a heartworm infestation, and it occurs in dogs with a moderate to large number of heartworms.
Diagnosis of Caval Syndrome in Dogs
Often, the symptoms of caval syndrome are not present, or only symptoms of heartworm disease are seen. Routine tests can show a heartworm infestation.
If heartworm is suspected, caval syndrome can be detected with a blood test. Two blood tests are used for this, the Knott’s test and the ELISA test. If your dog tests positive for heartworms, then your veterinarian will use chest x-rays, echocardiography, electrocardiography, and ultrasounds to assess the extent of the heartworm migration.
Before any treatments are started, routine lab work is done to make sure the liver and kidneys are functioning properly, as they can be adversely affected by the drug used to kill the adult heartworms.
Treatment of Caval Syndrome in Dogs
Caval syndrome is an advanced stage of heartworm disease and has a poor rate of survival. It carries a 14% to 42% risk of death, even with heartworm removal. Without treatment, death generally occurs within 24 to 72 hours. Organ failure leading to death can occur before or after treatment. Heartworm removal from the vena cava, right atrium, and right ventricle will need to be undertaken immediately for your dog to have the best chance of survival.
Before the heartworms are treated, any heart failure, liver disease or kidney disease present is treated first. Shock is treated with supportive care, such as intravenous fluids that can be given before or after surgery.
Then, surgical removal of the heartworms is recommended before any other treatments. This entails the administering of sedation or anesthesia, then using forceps to grasp and pull the heartworms out of the heart manually through the jugular vein. This is guided by an echocardiograph. This treatment can fail if hypothermia, fluid accumulation in the abdominal cavity, or an elevation in pressure in the central vein occurs after surgery.
Corticosteroids, heparin, and antibiotics may be administered after surgery. Urine color, blood urea nitrogen, and the level of red blood cells are closely monitored after heartworm removal. Some dogs may need oxygen therapy.
Once the blood urea nitrogen level, blood cell counts, breathing rate and appetite of your dog has returned to normal, an adulticide is often recommended to kill any worms still remaining. Common drugs are melarsomine. milbemycin, and selamectin. Ivermectin may be administered, but has some medical risks, such as pulmonary embolism.
Recovery of Caval Syndrome in Dogs
If your dog has undergone surgical heartworm removal, he will be released to go home once he has stabilized. With successful surgery, improvement in cardiac output, a reduction in vein pressure, a decrease in anemia, and a resolved hemoglobinuria can be seen, usually within several days.
Your veterinarian will most likely recommend an adulticide to treat the remaining heartworms, and this can be given at home for up to 18 months. Often, a visit for a blood test will be scheduled 4 to 6 months after treatment to check on the level of adult heartworms still present. If positive, the adulticide may be continued.
With treatment, recovery can vary from a return to normal activity to persisting liver or kidney problems, irreversible lung changes, and a lifetime of medication. This will depend on the severity of the condition prior to treatment.
Preventing a heartworm infestation is an important part of recovery, and of protecting your dog from becoming infected at all. Since mosquitoes need to be present to deliver an infected bite, keep your dog away from mosquito infested areas. Use a mosquito prevention, such as a spot treatment, and give your dog monthly heartworm pills to prevent an infestation.
Caval Syndrome Questions and Advice from Veterinary Professionals
We adopted a dog from a shelter at "9 months" old in December 2016, He tested negative for heartworm, they gave him preventative, January took him to vet for first follow up he had heavy breathing we were concerned about, they said it was because he was young and excited. The heavy/rapid breathing continued but he had so much energy all the time so we exercised him and trained him. Now in July 2017 he tested positive for heartworm, we missed feb, march and april of the heartguard but he has dec, jan, may, june, july. He tested positive for Adult female heartworm. Now we have to decide what to do, he is a puppy about 1 yr old, but the treatment is expensive and he most likely had Heartworm in december because it takes 7 months to show adult heartworm and he had always had heavy breathing. Could a puppy have Caval Syndrome, our doctors want so much money for his treatment and pre- testing and if there is a chance he could die anyway we would rather spend all the time we have with him and keep him happy, then spend $1000 to try and treat him and he still dies. He is very active and trying to keep him calm and still is really hard he just spins in circles until we let him out, we built a 6x6x6 ft cage in our house so he can move and be comfortable but not run around. We are dedicated but i dont know how else to tell how severe this is and its going to cost a lot just for the Chem 11, CBC, microfluria, Snap Heartworm , lyme and echliria test, and his doxycycline 100 MG BID x 30 days. We keep trying to call other hospital to get better pricing but no one will give us answers, they all want us to see their doctor first, and frankly I feel bad we exercised him in the beginning because we didn't know he had this, so i would like his treatment to start as soon as possible but we feel like we are running out of options and cant find resources to help. We are trying to decide if everything xrays and blood work are all necessary tests or if our vet is just clearly trying to take our money. We have told them we cant afford their treatment but they keep saying everything is necessary and we dont have the money to just keep bringing him to consults with other vets until we find a cheaper one. I read about this caval syndrome and how some dogs can even be resistant to Heartworm medicine. I am just nervous we found him in bad circumstances and now have no options. Thank you for any input.
Caval syndrome is a severe form of heartworm infection which may occur in up to 20% of heartworm cases; in Caval syndrome, there is a high level of red blood cell damage which releases hemoglobin which is excreted by the kidneys which turns the urine brown or black. Whilst I understand your concern, further testing is required to get a better picture of the severity of the condition; once the severity of the heartworm infection is determined a treatment plan may be initiated which includes medicines, supportive care (fluids etc…) and surgery (if required). Like other Veterinarians, I am unable to comment without examining Loki and performing some tests (they are necessary). If you are concerned about your Veterinarian’s intentions, it may be best to see another Veterinarian for another opinion. Regards Dr Callum Turner DVM
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My dog is 2 and an american bulldog. He was diagnosed with heartworm and three days ago had his last two immiticide injections. When i took him home he had loody diarrahea, at one point it only looked like blood. But since that day (which was after his last immitcide) he hasnt had any more bleeding but his stomach seems very bloated and he is very lethargic and is drinking large amounts of water. My vet has been very unhelpful and didnt do any further work up or testing after the initial heartworm positive blood test and did not do any test for caval syndrome. Are the symptpms he has had since the immiticide any indictation of caval syndrome and should i get a new vet to test him?
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Hi- we recently took our dog (she's 6) to the vet. This is our fault, but she's never been on heart worm preventive. She started acting strange a day ago. She's a Jack Russell Terrior so she likes to run, chase squirrels, etc. She hasn't been very active for a few days, but she's been eating and drinking just fine. No cough or anything. The strange thing was she urinated in my house (which is very unlike her) and it was a little dark- not brown just darker.. we thought she may be dehydrated or UTI. We did take her to the veterinary today and found out she did test positive for heart worms. My heart is broken, but we're wanting to do everything we can to get her through this! Just wondering- what's the likelihood that we get her better and get to the point of killing these heartworms ? I know there's really no way to tell and everyone is different, but she's had NO symptoms until a day ago! The vet said on a scale of 1-10 (with 10 being the worst) hers was a 7. We did an x ray and it showed some heart enlargement and she also has a little inflammation in her lungs. We are just concerned that the heart worms will just progressively get worse before we are able to treat them, but we know we need to get her better first.
As you have mentioned, each case is different and I also do not wish to give you any false hope either; but treatment may include surgical removal of heartworms in some cases, your Veterinarian would be able to guide you better. As far as prognosis is concerned, treatment and the response to treatment is the main component; medications to kill any microfilariae and if appropriate any adults. As I haven’t examined Molly, I cannot give you any indicate to treatment as treatment plans vary depending on severity and Veterinarian’s discretion (can a dog handle it this soon etc…). I’ve added some information from reputable sources below for you. Regards Dr Callum Turner DVM
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