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A Holstein cow presented for weight loss and anorexia had tachycardia, heart murmur, and a chronic inflammatory process. Serum cardiac troponin I was increased at 3.52 ng/mL. Transthoracic echocardiography revealed a thickened tricuspid valve and comet-tail artifacts compatible with gas in the affected area. This report suggests that serum cardiac troponin I may be increased in bacterial endocarditis in cattle.
Endocardite tricuspide bovine comme cause d’une concentration accrue des troponines cardiaques. Une vache Holstein présentée pour perte de poids et anorexie avait de la tachycardie, un souffle cardiaque et un processus inflammatoire chronique. Les troponines I cardiaques étaient augmentées à 3,52 ng/mL. L’échocardiographie transthoracique a révélé une valvule tricuspide épaissie et des artefacts de queue de comète avec du gaz dans la région touchée. Ce rapport suggère que les troponines cardiaques I sériques peuvent être accrues dans les cas d’endocardites bactériennes chez les bovins.
(Traduit par Isabelle Vallières)
Heart diseases in cattle are challenging with regard to their diagnosis and prognosis (1). Various biochemical parameters called cardiac biomarkers can be used for the diagnosis of bovine heart disease (1). The myocardial bound creatine kinase (CK-MB) is the specific cardiac isoenzyme of creatine kinase and can be increased in various heart disorders (1). Lactic dehydrogenase type 1 (LDH1) is also increased in heart disease (1). However, there is a lack of sensitivity of these markers in large animals (2). Bacterial endocarditis is a common heart disease in cattle (3,4). Animals typically present with chronic infectious process, undulating fever and heart murmur (3,4), but specific signs of cardiac disease may be absent.
A 3-year-old Holstein cow was presented at the bovine ambulatory clinic of the Faculté de Médecine de Vétérinaire for anorexia and decreased milk production of 1-week’s duration. The cow was in a dairy herd of 200 milking cows fed a total mixed ration (TMR) and kept in free stalls. The herd was routinely vaccinated for respiratory viruses — infectious bovine rhinotracheitis (IBR), bovine respiratory syncytial virus (BRSV), bovine parainfluenza 3 virus (PI-3), and for bovine virus diarrhea (BVD). The cow had calved 5 mo earlier without any problems except it had a poor body condition score [2.25 out of 5 (5) at calving as determined by routine preventive medicine program]. Analysis of the cow’s medical record did not reveal any problems (DS@HR, Saint-Hyacinthe, Québec).
On arrival, the cow was still in poor body condition (BCS of 2.25). The rectal temperature (38.8°C) and the respiratory rate (20 breaths/min) were normal. A slight tachycardia was noted (90 beats/min). Cardiac auscultation revealed a holosystolic IV/VI murmur with a point of maximal intensity on the right side of the thorax. The mucous membranes were pale with a capillary refill time of < 2 s. The rumen was hypo-motile (1 contraction per 2 min). A magnet was present in the reticulum as assessed with a compass. The transrectal examination was normal. No other abnormalities were observed on physical examination.
Blood samples were taken for a complete blood (cell) count (CBC), a serum biochemistry profile, cardiac troponin I (Beckman-Coulter Access AccuTnI; Beckman Coulter, Long Beach, California, USA) measured by a chemiluminescent assay that uses 2 mouse monoclonal antibodies directed against human cTnI. The lower limit of detection for this assay is 0.01 ng/mL. The cow was also prepared for a standard echo-cardiography (6,7), to investigate the origin of the murmur. The right side of the thorax was shaved from the 3rd to the 5th intercostal space. Water was then applied to the area to wash the skin and increase ultrasound penetration — a coupling gel was also applied. Cardiac ultrasonography was then performed with a 2-MHz sectorial probe (LogiqBook, GE Healthcare, Wauwatosa, Wisconsin, USA).
The echocardiographic findings were in accordance with a bacterial endocarditis of the right atrioventricular valve. The tricuspid valve was irregularly thickened (Figure 1). Small gas bubbles were also observed in the valve with multiple comet-tail artifacts that precluded complete visualization of the myocardium near the septal leaflet of the valvular attachment. Those findings were consistent with abcessation of the affected area and secondary gas production by bacteria. The tricuspid leaflet attached to the anterior right ventricular wall appeared to be normal as a thin echoic line (Figure 2). A dilation of the right atrium and ventricle was also noted (Table 1). The shortening fraction of the left ventricle was decreased at 27.8%. No myocardial anomalies were observed.
The CBC and serum biochemistry profile were compatible with a nonregenerative anemia (PCV = 19%; reference range: 24% to 36%) with no reticulocytes on the blood smear, a chronic inflammatory process with hyperfibrinogenemia (12 g/L; reference range: 3 to 5 g/L), hyperglobulinemia (62 g/L; reference range: 26.2 to 45.2 g/L), and hyperproteinemia (98 g/L; reference range: 59.5 to 80 g/L).
The serum cTnI concentration of the cow was markedly increased at 3.52 ng/mL (reference range: cTnI 0.00 to 0.05 ng/mL) (8,9). Due to the poor prognosis, no further tests were performed. The cow was culled and the owner was told that there was high risk that the cow would be condemned due to multiple signs of sepsis. Unfortunately it was not possible to perform a necropsy.
Valvular heart diseases are rare in cattle and are mainly due to bacterial endocarditis (3,4). Although the clinical findings in cases of bacterial endocarditis include a chronic infectious process, intermittent fever, tachycardia, and heart murmur (1,4), those signs lack specificity (1,10). A cardiac murmur has been detected on physical examination in 50% (3) to 80% (4) of confirmed cases of bacterial endocarditis. Both studies were performed under hospital settings in which conditions of cardiac auscultation are better than in the field. Serial blood cultures also may help in the diagnosis of infectious endocarditis in determining the bacteria present in the infected valves (11).
Transthoracic echocardiography is a sensitive tool for the antemortem detection of bacterial endocarditis in cattle (3,12,13). The ultrasonographic findings include an irregular valvular thickening and secondary lesions induced by regurgitation due to the diseased valve (1). The infected endocardium is usually echogenic (13). Heterogenic echogenicity with comet-tail artifacts and gaseous content of the infected endocardium encountered in this case have not been previously described in cases of bovine bacterial endocarditis. The image was interpreted as gas bubbles produced by the bacteria in the infected endocardium that lead to a reverberation artefact (14), which is frequently observed in cases of abscessation. It is not known if an abscessed valve could lead to the same finding, since a necropsy was not performed. The typical echocardiographic findings in human cases of abscess secondary to valvular endocarditis include a definite region with reduced echo density or echolucent cavities (15), which were not found in this case.
Although echocardiography is helpful for the diagnosis of bacterial endocarditis, this ancillary test is not widely used under field conditions. Cardiac troponins (cTn) are valuable indicators of myocardial cell necrosis and ischemia that have been used in humans (2), dogs (16), and horses (1). Troponins are contractile proteins that are specifically found in the cardiac myocyte and are released in the circulation in cases of ischemia of the cardiac cell (17). Cardiac troponin I (cTnI) has been recognized as more sensitive and specific than cardiac troponin T (cTnT) in humans (2). The serum cTnI concentration is correlated with the degree of heart dysfunction in canine heart diseases (16). The potential value of the cTnI concentration in cattle has been described in case reports of idiopathic pericarditis (8), 5 cases of pericarditis (18), 1 calf with viral myocarditis (19), and induced endotoxemia in calves (9).
Increased cTn concentrations in cases of bacterial endocarditis are frequently observed in humans (20), but have never been reported in other species. The increase in cardiac troponin concentration in these cases seems to be a manifestation of myocardial involvement (20). A recent study demonstrated that increased concentration of cTnI in cases of infective endocarditis was correlated with the presence of annular or myocardial abscesses diagnosed by echocardiography (21). The cTnI assessment could serve as a prognostic tool since patients with abscess and endocarditis have a poor prognosis (21). Patients with infective endocarditis and increased cTnI concentration are also more likely to have left ventricular systolic dysfunction (21). The left ventricular efficacy was altered in this case with a severely decreased shortening fraction of the left ventricle. Although the ultrasonographic aspect of the myocardium was normal in this case, a small portion of the interventricular septum could not be assessed because of the comet-tail artifacts due to the infected tricuspid valve. It is not known if this portion could have been abscessed since a necropsy was not performed.
This case report emphasizes the usefulness of transthoracic echocardiography for the diagnosis of bovine bacterial endocarditis and its repercussion on the cardiac morphology and function. This is the first case documenting an increased cardiac troponin I level in a cow with bacterial endocarditis. It remains to be determined whether cardiac troponin concentration can help in the prognosis of bovine heart diseases as it does in other species.
The authors thank Dr. Joel Lavoie for his valuable help in providing his expertise on the cardiac troponin concentration. CVJ
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