Dogs shed light on human arrhythmias.

Few animal models exist for studying arrhythmia, a common human disorder in which the heart periodically beats irregularly, sometimes resulting in sudden death. So researchers bred a group of German shepherds that is now providing valuable information about the disease, report N. Sydney Moise and her colleagues at Cornell University's College of Veterinary Medicine in an article accepted for publication in the Journal of the American Veterinary Medical Association.

The 270 dogs in Moise's group were bred to have arrhythmias in the heart's ventricle chambers. A predisposition to arrhythmias occurs almost exclusively in this breed, though the prevalence of the disorder remains unknown. Between 15 and 20 percent of dogs with the disorder die from it as puppies, usually while resting or sleeping, Moise says. The illness has no known treatment. Canine arrhythmias resemble fairly serious human cases, although dogs do not develop the dangerous blood clots that people sometimes do. The animals' condition also resembles sudden infant death syndrome, in which seemingly healthy infants die in their sleep.

Because puppies have no symptoms and no health problems other than the arrhythmias, researchers must monitor the animals' heart rates for 24 hours to determine whether they have the disorder. Generally, only puppies with three times the normal rate of roughly 100 beats per minute face a risk of dying from an arrhythmia.

These dogs have a problem with their autonomic nervous systems, Moise says. Their hearts lack nerve fibers that help control heart rate and rhythm.