Stage 4 Heart Worms in Dogs

A positive heartworm test is always serious for a dog and its owner. But when the disease progresses to its final stages, Level 4, it's critical and often fatal. It becomes known as Caval Syndrome, and surgery is often necessary and not always successful.

Heartworm is prevalent and, in some regions of the United States, epidemic. The disease is classified in stages, from lowest risk to the point where it reaches Caval Syndrome. As it progresses, symptoms become more intense and the likelihood of recovery diminishes.

Heartworms

Heartworms are literally worms--about the size of spaghetti, five to 14 inches long--that live in blood vessels and the right ventricle of a dog's heart. Dogs get heartworms when they are bitten by an infected mosquito. Dogs with heartworms have been diagnosed in all parts of the United States and around the world.

All dogs should be on a monthly heartworm preventative available from your veterinarian. Before it's prescribed, you dog must test negative for heartworm disease.

Disease Stages

There are three stages of heartworm disease before it reaches the point of Caval Syndrome or Stage 4.

Stage 1 occurs in young dogs, with little to no damage.

At Stage 2, dogs are coughing and have some difficulty breathing, and X-rays show damage. Blood work might also reveal the dog has kidney and liver damage.

At Stage 3, the dog has lost weight, is coughing and has difficulty breathing. X-rays reveal some damage, and blood tests indicate kidney and liver problems.

Caval Syndrome

Caval Syndrome (also known as Vena Cava Syndrome) occurs when there are lots of adult heartworms---usually more than 100---living in the dog's heart and completely blocking the flow of blood. The dog will collapse, go into shock and die within a couple days if not treated immediately.

Treatment

When heartworm disease reaches the point of Caval Syndrome, the only chance for the dog to survive often is surgery to remove some of the worms to allow for sufficient blood flow. If the pet survives, additional treatment to kill the remaining worms will be necessary. This is often done with injections of Immiticide or with monthly doses of Ivermectin.

Prognosis

By the time heartworm reaches Stage 3, survival rates fall from 95 to 80 percent. The prognosis for a dog in Stage 4 is "guarded."

References

• The Pet Center, Diana Beam DVM
• Westwood Animal Hospital