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Heart: myocarditis
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) 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.
Presenting signs
- Concurrent systemic illness or history of exposure to toxic substance.
- Signs of cardiac dysfunction.
- No pathognomonic signs.
Geographic incidence
- In areas of world where certain infectious diseases are endemic, eg Trypanasoma cruzi (South-East USA), Rickettsia rickettsii (Rocky Mountain Spotted fever, USA), Leishmania (worldwide) and possibly Borrelia burgodorferi (Lyme's disease USA, Europe).
Age predisposition
Viral myocarditis
- 1-6 months (peak at 4-8 weeks of age), although can be seen in older unvaccinated dog Parvovirus disease associated with CPV-2.
- Other suggested etiology for myocarditis at <1 month include intrauterine:
- Distemper Canine distemper disease.
- CHV1 Canine herpesvirus disease.
- Occasional reports SHV1 infections.
Cost considerations
- Dependent on severity of myocardial involvement and ease of treatment of inciting agent.
Special risks
- Same as arrhythmia Heart: dysrhythmia or CHF Heart: congestive heart failure.
Pathogenesis
Etiology
Infectious causes
Viral myocarditis
- Parvovirus Parvovirus disease associated with CPV-2.
- Distemper Canine distemper disease.
- CHV1 Canine herpesvirus disease. Herpesvirus has only been shown to cause myocarditis experimentally but not in natural infections.
- Occasional reports SHV1 infections.
- 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
- Leishmania spp Leishmaniosis.
- Toxoplasma gondii Toxoplasmosis.
- Neospora caninum Neosporosis.
- Babesia canis Babesiosis.
- Trypanosoma cruzi Trypanosomiasis.
Bacterial myocarditis
- Bartonella spp Bartonella spp.
- Borrelia burgdorferi Borrelia burgdorferi.
- Clostridium spp Clostridia spp.
- Rickettsia rickettsii Rickettsia rickettsii.
- Staphylococcus spp Staphylococcus spp.
- Anaerobic infections Anaerobic bacterial infections: overview.
Predisposing factors
General
- Immunosuppression.
- Debility.
Specific
- Exposure to infectious agent 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 = arryhthmias/CHF.
- Often concurrent signs of systemic infection/toxicity.
- Severe systemic disease, eg GDV, 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.
- 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.