Degenerative Valvular Disease vs. Bacterial Endocarditis
The history and presenting clinical signs combined with echocardiography and repeated blood cultures are all key-factors to help differentiating between chronic valve disease (CVD) and bacterial endocarditis.
Bacterial colonization of a heart valve will generally produce vegetations that will disturb valve coaptation resulting in valvular regurgitation and development of a heart murmur. Consequently, a recently developed heart murmur is a key-finding in a febrile patient. Contrary to humans, most cases of bacterial endocarditis in small animals develop on healthy valves, and most dogs presented with bacterial endocarditis do not have underlying cardiac disease. Also the veterinary literature does not contain convincing evidence for dentistry-induced bacterial endocarditis.
Bacterial endocarditis is more commonly seen in dogs than in cats. Based on reported cases in the veterinary literature the typical patient is a male pure-bred medium-to-large size dog older than four years of age. Common clinical signs include depression/weakness, pyrexia, heart murmur, +/- bounding pulses.
Combined with the patient's history, clinical findings, and blood cultures, echocardiography is a pivotal tool in diagnosing endocarditis. Blood cultures lack specificity and sensitivity in dogs and cats and are as a result hardly ever solely relied upon to make a definitive diagnosis of bacterial endocarditis in small animals. Still, blood cultures must be obtained and their usage comes into play when seeking to identify the offending organism and decide on an appropriate treatment scheme. Repeated blood cultures are recommended prior to institution of antibiotic therapy.
The vast majority of infective endocarditis cases in small animal medicine have a bacterial etiology with a higher incidence of gram negative infections. Bacteremia is a prerequisite for bacterial colonization of the valve apparatus of the heart. Studies suggest that transient bacteremia is not an uncommon phenomenon in dogs and cats, but still the incidence of bacterial endocarditis is fairly low overall. When seen the disease usually takes an acute to subacute malignant course. Antibiotic therapy should ideally be based on results obtained from repeated blood cultures. A fairly aggressive therapeutical approach is ideal to keep the antibiotic serum concentration at the high end of the therapeutical scale for several weeks, as is warranted in this category of patients. Complications such as heart failure should be separately addressed using classical heart failure therapy (i.e., diuretic, angiotensin converting enzyme inhibitor, +/- digoxin). Corticosteroid administration is contraindicated and will exacerbate clinical signs and aggravate the prognosis in these cases.
Bacterial endocarditis generally gives a poor prognosis. Death is typically seen due to heart failure, embolic complications (including renal failure), or sepsis.
DEGENERATIVE VALVULAR DISEASE/MYXOMATOUS VALVULAR DEGENERATION
The number of synonyms in the veterinary literature for this disease is rather plentiful including names such as myxomatous valvular degeneration, chronic valvular disease (CVD), chronic degenerative valvular disease, endocardiosis, and others. For the sake of simplicity CVD has been used here when referring to myxomatous degeneration of the atrioventricular valves.
In cases of mild disease a heart murmur is often detected as an incidental finding on a routine physical exam of a geriatric dog. In relation to more progressed stages of CVD a history of coughing is often mentioned upon presentation, either due to main stem bronchial compression secondary to significant left atrial enlargement or early congestive heart failure and pulmonary edema. Exercise intolerance and weight loss may have been noted by the owner in patients with more severe disease. The mitral valve is most commonly affected, and consequently signs of left-sided heart failure are more frequent in these patients.
The incidence of CVD is undoubtedly much higher than any other cardiac disease seen in small animals. Leaving aside the Cavalier King Charles Spaniel, CVD is a disease affecting primarily middle-aged to older dogs. Small breeds are clearly more prone to develop CVD with certain breeds being predisposed for the condition. Large-breed dogs may, however, infrequently develop CVD. CVD can occasionally be seen in cats.
The clinical picture will inevitably vary pending on severity of the disease. Mild CVD leaves the animal asymptomatic, whereas more moderate disease can produce a cough. Dogs with severe CVD and secondary heart failure are often presented with a cough and tachypnea, and possibly dyspnea, tachycardia, exercise intolerance and cachexia. In the case of a ruptured chorda tendinae a more acute onset of symptoms will be observed.
The history, signalment and auscultatory findings are generally adequate to make a tentative diagnosis, as CDV is typically seen in small-breed geriatric dogs which are either asymptomatic or possible being presented with a cough, or in the case of concurrent heart failure, with more severe respiratory symptoms. To get a baseline of overall heart size and degree of left atrial enlargement, or to assess lung pattern if the patient has respiratory symptoms, a thoracic radiograph is warranted. Echocardiography can be used to assess the anatomy of the affected valve but is not truly critical in making the actual diagnosis of CVD.
Treatment is only warranted in patients with clinical symptoms secondary to their disease, as there is no evidence in the veterinary literature to suggest that anything slows down the progression of CVD. In patients with CVD and secondary heart failure standard heart failure therapy including diuretic(s), an angiotension converting enzyme inhibitor, and possible digoxin would be warranted. In patients where coughing persists, despite resolution of pulmonary edema due to heart failure, a cough suppressant may be warranted.
A diagnosis of CVD does not automatically mean that the patient will follow a fixed route and develop heart failure and ultimately death as a consequence of the disease. Some cases of mild CVD might never really progress to a point where symptoms occur, whereas other cases take a much more malignant course and develop massive valvular regurgitation and heart failure ultimately leading to death. The prognosis is therefore strongly pending on the speed at which the disease seems to progress over time in any given patient. Owners may be informed that most dogs with mild/moderate CVD take years before progressing into heart failure, and that the disease in a number of cases might in fact never progress significantly.
In summary,CVD and endocarditis tend to have quite different presentations and symptomatologies. A small-breed geriatric dog with a loud systolic heart murmur and possibly a cough is most likely to have CVD, whereas a larger breed dog presented with a history of lethargy and fever in which a newly developed loud heart murmur is detected is very suspicious of having bacterial endocarditis. On echocardiography the two disease processes often have a similar appearance. It is therefore pivotal to also assess the patient's history, physical exam findings and blood work to make a final diagnosis.
References are available upon request.