Endocarditis in cats

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Infection of the endocardium typically involves one of the cardiac valves, although mural endocarditis may occur. It is believed that endothelial damage must be present for infective endocarditis to develop. When the endothelium is partially eroded and underlying collagen exposed, platelets adhere and produce a thrombus. Blood-borne bacteria may become enmeshed in this thrombic lattice, resulting in a localized infection that causes a progressive destruction of the valve and results in valvular insufficiency. In dogs, horses, and cats, the aortic and mitral valves are most commonly affected. The tricuspid valve is rarely affected, and pulmonic valve infective endocarditis is exceedingly rare. In contrast, the tricuspid valve is the most commonly affected in cattle. Infective endocarditis is rare in cats, and there are no breed predilections. 

Bacteria released from the infected aortic or mitral valves enter the circulation and can colonize other organs; therefore, infective 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 fever is usually present. Shifting leg lameness may be reported, and weight loss and lethargy are present in almost all cases. If a right-sided valve is affected (tricuspid, pulmonic), 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; the exact type depends on the valve involved. When the aortic valve is affected, a low-grade diastolic murmur is present, with maximum intensity over the left cardiac base. A systolic murmur caused by increased stroke volume may also be noted. In this instance, arterial pulses are bounding due to diastolic run-off and increased stroke volume. Mitral valve endocarditis results in a murmur similar to that caused by degenerative valve disease—a low- to high-grade systolic murmur (intensity dependent on the degree of mitral insufficiency) heard best over the left cardiac apex.

Bacteria most often isolated from affected small animals include Streptococcus spp, Staphylococcus spp, Klebsiella spp, and Escherichia coli. Other bacterial species, protozoa (e.g. Toxoplasma gondii) and fungi (e.g. Cryptococcus spp) may be involved in feline patients. In humans, 60-80% of patients with infective endocarditis had a predisposing cardiac lesion that facilitated bacterial attachment. In dogs, however, infection appears to develop commonly in patients with no evidence of valve abnormalities. A blood test often shows a neutrophilic leukocytosis. Active infection may be associated with the presence of band neutrophils, and chronic infection with a monocytosis (90% of cases in one series). Anaemia of chronic disease is frequently present. Serum analysis abnormalities reflect organ involvement secondary to infective emboli and may include increases in liver enzymes, BUN, and creatinine. In patients that develop immune complex glomerulonephritis, significant urinary protein loss and hypoalbuminemia may develop. Blood cultures with sensitivity should be obtained in affected animals. It is preferable to draw 2 or 3 blood samples, each 1-2 hr apart, in a 24-hr period. A strict aseptic technique is required. Radiography demonstrates cardiac chamber enlargement, depending on the location and degree of insufficiency of the involved valve. If the aortic or mitral valve is affected, there will be left atrial and left ventricular dilatation. Evidence of left-sided failure may be seen as an increase in interstitial density or, in severe CHF, an alveolar pattern in the pulmonary parenchyma. If the tricuspid or pulmonic valve is affected, right-sided chamber enlargement is expected. Echocardiography is the diagnostic test of choice, as blood cultures are positive in only 50-90% of dogs. The affected valve is easily detected—the involved area is hyperechoic (bright) and thickened. Doppler echocardiography will confirm insufficiency of the valve, and chamber enlargement on the side of the affected valve is expected when significant insufficiency is present. Electrocardiography may demonstrate atrial and ventricular premature complexes. Infrequently, other arrhythmias such as atrial fibrillation or conduction disturbances are found. The height of the R waves may be increased (suggestive of left ventricular enlargement) and the width of the P wave increased (suggestive of left atrial enlargement).

Therapy is directed at controlling clinical signs of CHF, resolving any significant arrhythmias, sterilizing the lesion, and eliminating the spread of infection. The heart failure may be extreme and intractable if the aortic valve is significantly involved; the prognosis is grave in these cases. The prognosis is much more favourable when infection is mild and limited to one of the AV valves. Controlling heart failure requires the use of diuretics such as furosemide, ACE inhibitors, and, where myocardial failure or supraventricular arrhythmias are present, digoxin. Initially, parenteral antibiotics are indicated for 1-2 wk (which may be cost prohibitive), followed by oral antibiotics for 6-8 wk. Initial broad-spectrum bactericidal antibiotics (ampicillin and gentamicin or cephalothin and gentamicin) should be used and changed, if needed, based on sensitivity studies. Renal function should be monitored with gentamicin therapy. Fluoroquinolones such as enrofloxacin may be considered as an alternative to aminoglycosides if renal failure occurs. The prognosis is poor in most dogs. Those that respond to therapy will likely require long-term cardiac medications (eg, diuretics, vasodilators, digoxin) and frequent re-evaluations. In large animals, rifampin (5 mg/kg, PO, bid), together with another broad-spectrum antibiotic, has been demonstrated to improve short-term outlook. Aspirin (100 mg/kg, sid in ruminants and 17 mg/kg every other day in horses) or heparin (30 U/kg, SC, bid in ruminants and horses) may prevent further thrombus and vegetative growth in large animals.

Considering the poor clinical course, prevention is vital. When animals with predisposing cardiac disease (eg, subaortic stenosis, patent ductus arteriosus, ventricular septal defect, cyanotic congenital heart disease) are to be subjected to procedures with a potential to cause bacteremia (eg, dental scaling, tooth extractions), prophylactic use of a broad-spectrum antibiotic, although controversial, may be considered.