Myocarditis

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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.

The inner (endocarditis) and outer (pericarditis) linings of the heart may also be involved.

Causes of myocarditis in dogs include:

  • Conduction disorders
- Atrial fibrillation - causing myocardial ischemia[1]
- Mitral valve endocardiosis-induced atrial myocarditis[2]
- Polymyositis[3]
- Steroid-responsive meningitis-arteritis[4]
- lymphocytic-plasmacytic myocarditis[5]
- Babesia spp[6]
- Bartonella vinsonii subsp. berkhoffii - usually causes endocarditis as well[7]
- Borrelia burgdorferi
- Leishmania spp[8]
- Neospora caninum[9]
- Trypanosoma cruzi[10] - may result in chronic cardiomyopathy[11]
- Canine parvovirus - especially young pups[12]
- West Nile virus - encephalitis, myocarditis and polyarthritis[13]
  • Nutrition
- Mineral deficiency (eg, iron, selenium, copper)
- Vitamin E deficiency
- Pyometra-associated myocarditis[14]
- Chronic gastritis-associated atrial myocarditis (?Helicobacter spp)[15]
  • Miscellaneous
- Severe exertion, status epilepticus, heat stroke[16]

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[17] 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[18].

References

  1. Goldstein RN et al (2008) Prednisone prevents inducible atrial flutter in the canine sterile pericarditis model. J Cardiovasc Electrophysiol 19(1):74-81
  2. Woolley R et al (2007) Atrial myocarditis as a cause of sinus arrest in a dog. J Small Anim Pract 48(8):455-457
  3. Warman S et al (2008) Dilatation of the right atrium in a dog with polymyositis and myocarditis. J Small Anim Pract 49(6):302-305
  4. 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
  5. Church WM et al (2007) Third degree atrioventricular block and sudden death secondary to acute myocarditis in a dog. J Vet Cardiol 9(1):53-57
  6. Lobetti RG (2005) Cardiac involvement in canine babesiosis. J S Afr Vet Assoc 76(1):4-8
  7. Billeter SA et al (2012) Invasion of canine erythrocytes by Bartonella vinsonii subsp. berkhoffii. Vet Microbiol 156(1-2):213-216
  8. Torrent E et al (2005) Myocarditis and generalised vasculitis associated with leishmaniosis in a dog. J Small Anim Pract 46(11):549-552
  9. Meseck EK et al (2005) Use of a multiplex polymerase chain reaction to rapidly differentiate Neospora caninum from Toxoplasma gondii in an adult dog with necrotizing myocarditis and myocardial infarct. J Vet Diagn Invest 17(6):565-568
  10. 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
  11. Guedes PM et al (2009) Development of chronic cardiomyopathy in canine Chagas disease correlates with high IFN-gamma, TNF-alpha, and low IL-10 production during the acute infection phase. Vet Immunol Immunopathol 130(1-2):43-52
  12. Zhao J et al (2011) Origin and evolution of canine parvovirus - a review. Wei Sheng Wu Xue Bao 51(7):869-875
  13. Cannon AB et al (2006) Acute encephalitis, polyarthritis, and myocarditis associated with West Nile virus infection in a dog. J Vet Intern Med 20(5):1219-1223
  14. Hagman R et al (2007) Cardiac troponin I levels in canine pyometra. Acta Vet Scand 49:6
  15. Tyszko C et al (2007) Recurrent supraventricular arrhythmias in a dog with atrial myocarditis and gastritis. J Small Anim Pract 48(6):335-338
  16. 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
  17. 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
  18. 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
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