Endocarditis in Dogs
Dr. Arnold Plotnick
Endocarditis is an often fatal disease caused by an infection of the heart valves. The infection is usually caused by bacteria, although fungal endocarditis can occur as well on rare occasions. Endocarditis occurs infrequently in dogs, and is very rare in cats and is a difficult disease to diagnose. Dogs are more likely to get be affected by endocarditis as they get older, and male dogs are slightly more susceptible than female dogs. Pre-existing heart disease increases the risk of dogs developing bacterial endocarditis.
Endocarditis most commonly affects two of the four major valves in the heart: the mitral valve and the aortic valve. Endocarditis causes little growths called "vegetations," which affect the ability of the valves to function properly.
In order for the valves to become infected, there has to be a period of time when bacteremia, which is the presence of bacteria in the bloodstream, is occurring. In most cases, the cause of the bacteremia that leads to the endocarditis is never identified. Known causes of bacteremia include surgical procedures involving the oral, gastrointestinal, and urinary tract; dentistry procedures; intravenous catheterization; implantation of pacemakers; administration of drugs that suppress the immune system; and previous heart valve infections. Once introduced into the bloodstream, the bacteria, somehow manage to overcome the dog's immune defenses, and an infection on the valve in established. Vegetations grow at the site of infection and cause the valve to malfunction. This usually leads to heart failure.
Making a certain diagnosis of endocarditis can be very difficult. Usually there is a vague history of lethargy and poor appetite. Eventually, most dogs develop heart failure and demonstrate the common signs of coughing, shortness of breath, weakness, or collapse. Many clinicians refer to the disease as "the great imitator" because of the variety of clinical signs in patients with the disorder.
Bacterial endocarditis often leads to a condition called septic embolization, in which microscopic pieces of the vegetations (emboli) from the infected valves break off and enter the bloodstream. These emboli travel through the bloodstream and affect other organs in the body. The most commonly affected organs are the kidney and spleen, although the brain, intestine, and the heart may also be affected.
The immune system's response to embolization sometimes does more damage than good, often leading to arthritis and glomerulonephritis, a type of kidney inflammation. Embolization of the kidneys or the heart is a very serious consequence of endocarditis and can trigger a series of complications that may lead to a fatal outcome.
Sometimes, bacteremia can progress to a more serious condition called sepsis in which overwhelming infection in the bloodstream affects the blood flow to the vital organs. Sepsis often progresses further, and the patient succumbs to septic shock, in which blood pressure drops and many organs begin to fail. If this happens, the outcome is almost invariably fatal.