Infection of the endocardium typically involves one of the cardiac valves, usually the AV or aortic valves in dogs and cats. Endothelial damage, most commonly due to subaortic stenosis in dogs, is a predisposing factor for infectious endocarditis to develop; however, it is common for endocarditis to form on a normal valve. Immunodeficiency may be a predisposing factor.
When the endothelium is partially eroded and underlying collagen exposed, platelets adhere and produce a microthrombus. Bloodborne bacteria may become enmeshed in this clot, resulting in a localized infection that causes progressive destruction of the valve and usually results in valvular insufficiency. The tricuspid valve is rarely affected, and pulmonic valve infectious endocarditis is exceedingly rare in small animals. Infectious endocarditis is rare in cats, and there are no breed predilections. In dogs, middle-aged, large-breed dogs are predisposed, and males are more commonly affected than females.
Infected thrombi released from the infected aortic or mitral valves enter the systemic circulation and can embolize other organs and limbs; therefore, infectious endocarditis can produce a wide spectrum of clinical signs, including primary cardiovascular effects or signs related to the nervous system, GI tract, urogenital system, or joints. A chronic, intermittent or continuous fever is usually present. Shifting leg lameness may be reported, and weight loss and lethargy are frequently present. Acute to subacute mitral or aortic valve regurgitation can result in left heart failure (ie, pulmonary edema), along with clinical signs of tachypnea, dyspnea, and cough. If the tricuspid valve is affected, ascites and jugular pulsations may be present. Mastitis and decreased milk production can be noted in affected cattle. Hematuria and pyuria may also be noted. A cardiac murmur is present in most cases and varies according to the valve affected.
The bacteria that are most often isolated from dogs and cats with infectious endocarditis include Streptococcus, Staphylococcus, Klebsiella spp, and Escherichia coli, but a host of other bacterial species may be involved. Bartonella is also a recognized cause of aortic valve infectious endocarditis in dogs.
In cases of infectious endocarditis, a CBC often shows neutrophilic leukocytosis and anemia of chronic disease. Serum analysis abnormalities reflect organ involvement secondary to infectious emboli and may include increases in liver enzymes, BUN, and creatinine. In animals that develop immune complex glomerulonephritis, substantial urinary protein loss and hypoalbuminemia may develop. Blood cultures with antimicrobial sensitivity should be obtained in affected animals. If blood cultures are negative, the offending organism can sometimes be isolated from a urine culture.
Radiography may demonstrate cardiac chamber enlargement in infectious endocarditis, depending on the location and extent of insufficiency of the involved valve. Because blood cultures may be negative even in cases with bacterial lesions, echocardiography is the diagnostic test of choice. The affected valve is usually easily detected; the involved area is hyperechoic, thickened, and often vegetative (ie, looks like a cauliflower).
Treatment is directed at controlling clinical signs of heart failure, resolving any notable arrhythmias and sterilizing the lesion to prevent recurrent bacteremic showers. The heart failure may be severe and intractable if the aortic valve is extensively involved; the prognosis is grave in these cases. The prognosis is much more favorable when infection is mild and limited to one of the atrioventricular valves. Controlling heart failure requires the use of a diuretic, such as furosemide, an ACE inhibitor, and pimobendan. Initially in dogs, parenteral antimicrobials are indicated for 1–2 weeks (which may be cost prohibitive), followed by oral antimicrobials for at least 6–8 weeks. Initial broad-spectrum antimicrobials (a combination of ampicillin plus gentamicin or enrofloxacin, or cephalothin plus gentamicin) should be used and changed, if needed, according to antimicrobial sensitivity studies.
Antimicrobial prophylaxis is indicated in dogs with subaortic stenosis when any type of procedure that can result in appreciable bacteremia is performed. Routine antimicrobial prophylaxis for dental procedures is not warranted with other types of cardiac disease, especially in dogs with myxomatous mitral valve degeneration, because no evidence suggests that these dogs are at increased risk of infectious endocarditis.
