ISSN 2398-2950      

Heart: myocarditis

ffelis
Contributor(s):

Vetstream Ltd

Rachel Blake

Synonym(s): Inflammatory cardiomyopathy


Introduction

  • Myocardial inflammation, infiltrate and necrosis/degeneration of adjacent myocytes. 
  • Cause: classic myocarditis is related to inflammation due to exposure to either discrete external antigens such as bacteria, viruses, parasites or internal triggers such as autoimmune disease. In people, drug/toxin induced myocarditis is also recognized. 
  • Signs: variable - arrhythmias to congestive heart failure (CHF), thromboembolism and sudden death. 
  • Diagnosis: history and clinical signs (systemic illness), heart auscultation, electrocardiography, echocardiography, cardiac troponin I, endomyocardial biopsy, serology, blood culture. 
  • Treatment: specific treatment against inciting element plus treatment of arrhythmia/CHF. 
  • Prognosis: depends on severity and inciting agent/cause. 

Pathogenesis

Etiology

Infectious causes 

Viral myocarditis 
  • Feline immunodeficiency virus. 
  • Feline coronavirus (Feline infectious peritonitis Feline infectious peritonitis). 
  • Feline panleukopenia virus (possibly, association unclear).
  • SARS-CoV-2 variant B.1.1.7 has also been shown to be transmitted to pets and might be involved in myocarditis. 
Protozoal myocarditis  
Bacterial myocarditis  
Other causes 
  • Traumatic myocarditis. 
  • Immune-mediated myocarditis (eg eosinophilic myocarditis). 

Predisposing factors

General

  • Immunosuppression. 
  • Debility. 

Specific

  • Exposure to infectious agent (often cats that hunt) or use of myocardiotoxic substances such as doxorubicin Doxorubicin

Pathophysiology

  • Inflammation of heart muscle caused by infectious/toxic agent(s) affecting pericardium, myocytes, interstitial or vascular tissue of heart. 
  • May be acute or chronic if infectious. 
  • Can result in cardiac dysfunction. 
  • Infection may arise locally, including valvular tissue, or be spread from distant sites, eg dental, prostate, skin, uterus, lung. 
  • Infection/toxicity → toxin (local or blood borne)/immune-complex/direct invasion → vasculitis/myocyte damage → myocardial inflammation → cardiac dysfunction = arrhythmias/CHF. 
  • Often concurrent signs of systemic infection/toxicity. 
  • Severe systemic disease, eg trauma, IMHA → sympathetic '‘storm'’ and release of free radicals → myocardial necrosis → arrhythmias. 

Timecourse

  • May have acute (days), or chronic (months) course. 
  • Acute disease may progress to a form of cardiomyopathy and eventually heart failure. 

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed Papers

  • Recent references from PubMed and VetMedResource
  • Chetboul V et al (2021) Myocarditis and Subclinical-Like Infection Associated With SARS-CoV-2 in Two Cats Living in the Same Household in France: A Case Report With Literature Review Front. Vet Sci 8, 748869 PubMed doi.org/10.3389/fvets.2021.748869. 
  • Ferasin L et al (2021) Infection with SARS-CoV-2 variant B.1.1.7 detected in a group of dogs and cats with suspected myocarditis. Vet Rec 189(9), e944 PubMed doi: 10.1002/vetr.944.
  • Ernandes M A et al (2019) Feline coronavirus-associated myocarditis in a domestic longhair cat.J Feline Med Surg Open Reports 5(2), 2055116919879256 PubMed doi: 10.1177/2055116919879256
  • Kegler K et al (2018) Fatal infection with emerging apicomplexan parasite Hepatozoon silvestris in a domestic cat. Parasites Vectors 11, 428 PubMed doi: org/10.1186/s13071-018-2992-4
  • McEndaffer L et al (2017) Feline Panleukopenia Virus Is Not Associated With Myocarditis or Endomyocardial Restrictive Cardiomyopathy in Cats. Vet Pathol 54(4), 669-675 PubMed doi: 10.1177/0300985817695516
  • Bestetti G &  Zwahlen R (1985) Generalized Parvovirus Infection with Inclusion-Body Myocarditis in Two Kittens. J Comp Pathol 95(3), 393-397 PubMed
  • Rolim V M et al (2016) Myocarditis caused by Feline Immunodeficiency Virus in Five Cats with Hypertrophic Cardiomyopathy. J Comp Pathol 154(1), 3-8 PubMed

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