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 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 cats, there are no breed predilections. Endocarditis can be seen at any age, depending on the cause, although thromboembolism-induced endocarditis typically affected cats over 7 years of age.
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. Haematuria 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.
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. In severe congestive heart failure (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 favorable when infection is mild and limited to one of the AV valves. 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 cats.
- Macdonald, KA (2009) Infective endocarditis. In Bonagura, JD & Twedt, DC (Eds): Kirk's current veterinary therapy. XIV. Saunders Elsevier, Missouri, pp:786-791
- Breitschwerdt EB et al (2010) Bartonellosis: an emerging infectious disease of zoonotic importance to animals and human beings. J Vet Emerg Crit Care (San Antonio) 20(1):8-30
- Cherubini GB et al(2007) Rostral cerebellar arterial infarct in two cats. J Feline Med Surg' 9(3):246-253
- Chomel BB et al (2006) Bartonella infection in domestic cats and wild felids. Ann N Y Acad Sci 1078:410-415