What is Caval Syndrome?
Caval syndrome is the result of heartworms migrating through the pulmonary artery to the right ventricle and into the right atrium of the heart. Once residing in the right atrium and venae cavae, they disrupt proper functioning of the tricuspid valve, which separates the chambers of the heart. Pulmonary hypertension (high blood pressure in the lungs) and reduced cardiac output result. In addition, caval syndrome can result in damage to the red blood cells, which carry oxygen throughout the body, as these cells travel through the masses of worms and become compromised. This syndrome may affect other organs in the body and is also known as liver failure syndrome, as liver functioning can be severely affected as well. Although not as frequently seen in cats as in dogs, caval syndrome is an urgent, life-threatening condition requiring immediate veterinary attention.
Caval syndrome is a complication of chronic heartworm that occurs when a large number of these worms invade the right side of the heart, impairing heart function. Usually, a large or chronic heartworm infection is required for caval syndrome to occur, but because of their smaller size, cats can be affected by this disease when they are hosting a relatively small heartworm population.
Symptoms of Caval Syndrome in Cats
Symptoms of caval syndrome in cats can be a direct result of decreased heart functioning, damaged red blood cells, or due to secondary damage to other organ systems. The most common symptom to initially manifest in cats is respiratory distress.
Other symptoms of decreased heart function and red blood cell damage include:
- Loss of appetite
- Weight loss/anorexia
- Inability to exercise
- Irregular heartbeat - right-sided cardiac murmur
- Issues with blood clots and/or hemorrhaging
- Heart failure
Secondary symptoms of liver and other organ system failure may also occur and include:
- Blood in the urine
- Hepatic (liver) dysfunction
- Renal(kidney) dysfunction
Causes of Caval Syndrome in Cats
Heartworms reside in both the wild and domestic animal populations. Dogs and wild canines are the primary hosts, but cats and other mammals can also be hosts. Heartworm larvae are transmitted by mosquitos and not from direct contact between infected animals. Mosquitos carrying the heartworm larvae are more common in some areas than others; consult your veterinarian to determine if you reside in an area commonly affected by heartworm infestations, as medication to prevent heartworm infestation is available for cats.
Heartworms are not as common in cats as they are in dogs and as a result cat are considered somewhat resistant as hosts. Typically, heartworms reside in dogs for several years and can occur in large numbers. In cats, heartworms are usually thought to only live two to three years and in much smaller numbers. However, due to their smaller size less worm load is required for complication like caval syndrome to occur in cats. Caval syndrome is caused by the migration of heartworms through the pulmonary artery into the right ventricle, right atrium, and right vena cava of the heart where they cause damage to structures and red blood cells, resulting in heart failure and other organ failure.
Diagnosis of Caval Syndrome in Cats
Your veterinarian will perform a complete physical exam of your cat to determine if caval syndrome may be present. You will be asked to provide a complete medical history, discussion of symptoms, and description of symptom onset in order to determine if caval syndrome may be present and to rule out other diseases responsible for your pet’s condition. Complete urine and blood work may be performed to rule out other causes for your cat’s symptoms. If caval syndrome is suspected, an antigen blood tests for heartworm may be performed to see if a heartworm infection is present. Microfilaria test may also be performed to determine if heartworms are present but this test is not as effective at detecting heartworms in cats, as heartworms produce less microfilariae in feline hosts. X-rays and ultrasounds may be ordered which will reveal heartworm masses in the cat’s heart.
Treatment of Caval Syndrome in Cats
Treatment of caval syndrome consists of supportive care and removal of the heartworm mass from the heart. Supportive care may include intravenous therapy, steroids, antibiotics, and oxygen therapy for animals experiencing symptoms of heart failure or other organ failure.
Surgery to remove the heartworm mass involves passing extraction forceps or a wire with a bristle brush down the jugular vein, into the vena cava, and extracting the heartworm mass. This process is aided by ultrasound guidance.
Surgical removal is usually followed by medication to remove heartworms in dogs. However, the medication used to combat heartworm infections in dogs is toxic to cats and therefore no medication is currently available for cats to remove heartworm infections once they have become infected.
Prognosis for this disease is poor, especially if the condition is in its advanced stages and organ failure has begun. Surgical intervention is very invasive and medication for removal of heartworm infection in cats once they are infected is not available. Euthanasia may be considered an option.
Recovery of Caval Syndrome in Cats
Prognosis is extremely guarded as surgery is very invasive and medication to remove remaining heartworm infection is toxic to cats. Recovery may take several days, during which time, intensive supportive care will be required.
Preventative worming for heartworm is the best defense against heartworm and caval syndrome. It is recommended that pet owners avail their pets of the medication to prevent heartworm infestation if exposure to mosquitos carrying heartworm larvae is possible.