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Myocarditis is a focal or diffuse inflammatory heart disease of the dog characterized by heart muscle (myocyte) degeneration or necrosis causing an adjacent inflammatory infiltrate.
Causes of myocarditis in dogs include:
- Conduction disorders
- - Atrial fibrillation - causing myocardial ischemia
- - Mitral valve endocardiosis-induced atrial myocarditis
- - Polymyositis
- - Steroid-responsive meningitis-arteritis
- - lymphocytic-plasmacytic myocarditis
- - Babesia spp
- - Bartonella vinsonii subsp. berkhoffii - usually causes endocarditis as well
- - Borrelia burgdorferi
- - Leishmania spp
- - Neospora caninum
- - Trypanosoma cruzi - may result in chronic cardiomyopathy
- - Canine parvovirus - especially young pups
- - West Nile virus - encephalitis, myocarditis and polyarthritis
- - Mineral deficiency (eg, iron, selenium, copper)
- - Vitamin E deficiency
- - Pyometra-associated myocarditis
- - Chronic gastritis-associated atrial myocarditis (?Helicobacter spp)
Clinical symptoms may be subtle, but include an auscultatable murmur and an abnormal rhythm may be detectable on ECG such as atrial fibrillation or premature ventricular complexes. Sudden deaths are unfortunately common and prodromal signs may be absent.
Blood tests may reveal a neutrophilic leukocytosis and hyperfibrinogenemia. Radiographs may show cardiomegaly, but subtle myocardial damage may require echocardiography to better identify altered myocardial activity. ECGs may reveal bundle branch block.
Diagnosis usually requires postmortem cardiac histological analysis for confirmation, although cardiac isoenzymes creatine kinase, lactate dehydrogenase and cardiac troponin (> 0.06 μg/L) are often increased and are correlated with a poorer prognosis.
Treatment usually involves cardiac contractility drugs such as digoxin or dobutamine, as well as furosemide for control of secondary pulmonary edema. Although NSAIDs such as tolfedine or meloxicam may be instrumental at minimizing inflammatory changes within the myocardium, prednisolone may be more appropriate in cases of possible underlying immune-mediated etiologies.
Recent research shows the promising benefits of adenosine and adenosine A receptor agonists in reducing myocardial damage during recovery.
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- Snyder K et al (2010) Arrhythmias and elevated troponin I in a dog with steroid-responsive meningitis-arteritis. J Am Anim Hosp Assoc 46(1):61-65
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- Caldas IS et al (2012) Myocardial scars correlate with eletrocardiographic changes in chronic Trypanosoma cruzi infection for dogs treated with Benznidazole. Trop Med Int Health Oct 29
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- Tyszko C et al (2007) Recurrent supraventricular arrhythmias in a dog with atrial myocarditis and gastritis. J Small Anim Pract 48(6):335-338
- Mellor PJ et al (2006) High serum troponin I concentration as a marker of severe myocardial damage in a case of suspected exertional heatstroke in a dog. J Vet Cardiol 8(1):55-62
- Silvestrini P et al (2012) Serum cardiac troponin I concentrations in dogs with leishmaniasis: correlation with age and clinicopathologic abnormalities. Vet Clin Pathol Sep 12
- Glover DK et al (2005) Reduction of infarct size and postischemic inflammation from ATL-146e, a highly selective adenosine A2A receptor agonist, in reperfused canine myocardium. Am J Physiol Heart Circ Physiol 288(4):H1851-H1858