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Basics ⬇

Basics

Definition

  • Inflammation of the heart muscle, often caused by infectious agents affecting the myocytes, interstitium, vascular elements, or pericardium.
  • Viral, bacterial, rickettsial, fungal, and protozoal diseases are all associated with myocardial inflammation (i.e., myocarditis).
  • Pharmacologic agents (e.g., doxorubicin) can also be causative.

Pathophysiology

  • Mechanisms-toxin production, direct invasion of myocardial tissue, and immune- mediated myocardial damage; vasculitis associated with systemic disease; allergic reactions and direct myocyte damage caused by pharmacologic agents. Protozoa (e.g., Trypanosoma cruzi) lead to granulomatous myocarditis; viral myocarditis is associated with cell-mediated immunologic reactions.
  • Myocardial involvement may be focal or diffuse. Clinical manifestations depend on the extent of the lesions. Diffuse, severe involvement may lead to global myocardial damage and CHF; discrete lesions involving the conduction system may cause profound arrhythmias.

Systems Affected

  • Systemic organ involvement depends on the causative agent
  • Cardiovascular-myocardial failure or arrhythmias
  • Respiratory-if pulmonary edema develops

Incidence/Prevalence

  • Viral myocarditis (e.g., parvovirus, distemper virus, and herpesvirus)-rare; very young puppies in their first months of life may be profoundly affected; in a second form (parvoviral), dilated cardiomyopathy develops in dogs 5–6 months of age that were infected during their first weeks of life.
  • Protozoal myocarditis associated with T. cruzi (i.e., Chagas disease) reported in dogs <2 years old from the southeastern United States. Males are more commonly affected than females. Toxoplasma gondii occasionally causes myocarditis. Immunosuppressed animals (e.g., cats with feline leukemia virus) are at high risk. Hepatozoon canis reported in dogs living in the Texas Gulf region.
  • Fungal myocarditis-primarily seen in association with systemic fungal infection; myocardial involvement varies with regional prevalence and prevalence of the systemic manifestation.
  • Bacterial myocarditis-can be caused by generalized sepsis and bacteremia.
  • Doxorubicin cardiotoxicity-reported in dogs receiving cumulative doses = 150–240 mg/m2.
  • Spirochetal myocarditis associated with Borrelia burgdorferi-documented in 10% of humans with Lyme disease; incidence and prevalence in dogs not well documented.

Geographic Distribution

Suspect myocarditis associated with infectious agents wherever these diseases are endemic (see above).

Signalment

Species

Dog and cat

Mean Age and Range

Viral myocarditis-seen primarily in animals <1 year of age

Signs

General Comments

  • Related to the degree and location of myocardial involvement.
  • Range from those of arrhythmias to those of CHF.
  • Onset of cardiac dysfunction in association with systemic illness or the use of specific pharmacologic agents is often the hallmark of myocarditis.

Historical Findings

  • Coughing, exercise intolerance, dyspnea-associated with CHF.
  • Syncope and weakness-associated with arrhythmias.
  • Concurrent systemic manifestations-often seen with infective myocarditis.
  • Use of antineoplastic or other pharmacologic agents-associated with the onset of cardiac dysfunction.

Physical Examination Findings

  • Gallop rhythm or murmur may be found-depends on the nature of the myocardial damage.
  • Arrhythmias-may be auscultated.
  • Fever-common in patients with active infection associated with myocarditis.

Causes

  • Virus (e.g., parvovirus, distemper virus, herpesvirus, West Nile virus).
  • Protozoa (e.g., Trypanosoma cruzi, Toxoplasma gondii, Neospora caninum, Hepatozoon Canis, Babesia spp., and Leishmania spp.).
  • Bacteria (e.g., Bartonella vinsonii subsp. Berkhoffii).
  • Fungus (e.g., Cryptococcus neoformans, Coccidioides immitis, Blastomyces dermatitidis, and Aspergillus terreus).
  • Algae (e.g., Prototheca spp.).
  • Doxorubicin.

Risk Factors

  • Exposure to infectious agents
  • Use of myocardiotoxic compounds
  • Immunosuppression
  • Debilitating diseases

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

  • Always consider preexisting heart disease, including congenital defects, cardiomyopathy, and acquired valvular disease.

  • History of a heart murmur or the presence of arrhythmias before onset of systemic illness helps differentiate from other diseases.
  • Extracardiac organ involvement and identification of infectious agents may aid in the diagnosis.

CBC/Biochemistry/Urinalysis

Abnormalities-vary, depending on organ involvement.

Other Laboratory Tests

  • Serologic tests to help identify an infectious agent.
  • Cytologic examination of pericardial, pleural, and peritoneal effusions to identify the infectious organism.
  • Blood culture to diagnose bacteremia.
  • Troponin-levels may be high.

Imaging

Thoracic Radiographic Findings

  • Cardiac silhouette may appear large or normal depending on the extent of involvement.
  • Pulmonary edema, congestion, or pleural effusion in patients with CHF.
  • Globoid heart in some animals with pericardial effusion.
  • Pulmonary granuloma may be found in animals with granulomatous myocardial infection.

Echocardiographic Findings

  • Reflect the extent of myocardial damage; may be normal if lesions are small or primarily affect the conduction system.
  • Pericardial effusion in some patients; pericardium may appear thickened and hyperechoic, depending on the extent of pericardial involvement.
  • Myocardium may appear mottled with patchy areas of hyperechogenicity caused by myocardial inflammation, fibrosis, or granulomas.
  • Regional dyskinesis caused by focal involvement may be appreciated on 2-D echocardiography.

Angiography

  • Because of the quality and non-invasive nature of echocardiography, cardiac catheterization is rarely indicated for the diagnosis.
  • May use angiography to detect specific chamber involvement or pericardial effusion, if echocardiography is not available.

Diagnostic Procedures

Electrocardiographic Findings

  • Heart enlargement patterns in some patients-depending on the extent of chamber involvement.
  • Arrhythmias-include both atrial and ventricular tachyarrhythmias.
  • Differentiate right and left bundle branch blocks and hemiblocks from ventricular enlargement patterns.
  • Atrioventricular nodal conduction disturbances in some patients.

Endomyocardial Biopsy

  • Useful for detection of infectious agents (e.g., protozoa, fungal elements) or inflammatory cell infiltrates.

Pericardiocentesis

  • Alleviates pericardial effusion.
  • Submit fluid for cytologic examination and possible bacterial culture.

Holter Monitor Study

  • To detect arrhythmias, frequency, and severity.
  • To monitor antiarrhythmic therapy.

Pathologic Findings

  • Dilated cardiac chambers with patchy areas of hyperemia, necrosis, or fibrosis.
  • Granulomas seen grossly in some patients.
  • Microscopic examination of the myocardium or pericardium may reveal inflammatory cells (e.g., lymphocytes, plasma cells, and macrophages), patchy fibrosis, or the infectious agents themselves.
  • Myofiber dropout-seen in patients with doxorubicin toxicity.

Treatment ⬆ ⬇

Treatment

Appropriate Health Care

  • Hospitalize patients with CHF for initial medical management.
  • Hospitalize patients with severe ventricular arrhythmias for initial antiarrhythmic therapy.
  • Hospitalize patients with severe systemic manifestations for aggressive medical therapy.

Activity

Restricted

Diet

Sodium restriction if CHF

Client Education

  • Cardiac manifestations may persist even with resolution of systemic illness.
  • Certain arrhythmias (i.e., ventricular tachyarrhythmias) may predispose to sudden death.
  • Antemortem diagnosis may be difficult.
  • Some infectious agents may pose a public health risk.

Surgical Considerations

Complete atrioventricular block may require pacemaker implantation.

Medications ⬆ ⬇

Medications

Drug(s) Of Choice

  • If a specific etiologic agent is identified, direct treatment against it.
  • Tailor antiarrhythmic therapy to the predominant arrhythmia.
  • Treat CHF with furosemide (1–2 mg/kg PO q6–12h), enalapril (0.25–0.5 mg/kg PO q12–24h), and digoxin (0.22 mg/m2 PO q12h) or pimobendan (0.25 mg/kg PO q12h).

Contraindications

Public health considerations may preclude treatment of some infectious diseases (i.e., T. cruzi).

Precautions

  • All antiarrhythmic drugs have proarrhythmic properties and should be monitored closely.
  • Systemic organ involvement (e.g., renal involvement) may necessitate modifying drug dosages or use of various cardiac drugs; monitor systemic function carefully.

Follow-Up ⬆ ⬇

Follow-Up

Patient Monitoring

  • Antiarrhythmic therapy-frequent auscultation and ECG
  • Serologic titers when appropriate
  • Auscultation and follow-up radiographs-treatment of CHF
  • Hemograms and serum biochemical analysis-systemic effects

Prevention/Avoidance

  • Avoid breeding animals with a poor vaccination history.
  • Avoid endemic areas if possible.
  • Monitor ECG and echocardiogram when using doxorubicin.

Expected Course and Prognosis

  • Depend on the extent and severity of myocardial involvement.
  • Many systemic fungal and protozoal diseases do not respond well to medical management.
  • Patients with extensive myocardial inflammation, degeneration, and signs of CHF-very poor prognosis.
  • Patients with isolated, controllable arrhythmias-good prognosis if the underlying cause can be treated successfully.

Miscellaneous ⬆

Miscellaneous

Associated Conditions

Often accompanies systemic illness

Age-Related Factors

Viral myocarditis-most often seen in animals <1 year old

Zoonotic Potential

  • Varies with infectious agent involved
  • May be high with protozoal and mycotic infections

Pregnancy/Fertility/Breeding

Some viral diseases (e.g., canine herpesvirus and parvovirus) have been passed to the fetus during pregnancy.

Abbreviations

  • CHF = congestive heart failure
  • ECG = electrocardiogram

Suggested Reading

Breitschwerdt EB, Atkins CE, Brown TT, Kordick DL, Snyder PS. Bartonella vinsonii subsp. berkhoffii and related members of the alpha subdivision of the Proteobacteria in dogs with cardiac arrhythmias, endocarditis, or myocarditis. J Clin Microbiol 1999, 37(11):3618–3626.

Cannon AB, Luff JA, Brault AC, et al. Acute encephalitis, polyarthritis, and myocarditis associated with West Nile virus infection in a dog. J Vet Intern Med 2006, 20(5):1219–1223.

Kraus MS, Gelzer ARM, Moise S. Treatment of cardiac arrhythmias and conduction disturbances. In: Smith FWK ,Tilley LP, Oyama MA, Sleeper MM, eds., Manual of Canine and Feline Cardiology, 5th ed. St. Louis, MO: Saunders Elsevier, 2015 (in preparation).

Lobetti RG. Cardiac involvement in canine babesiosis. J S Afr Vet Assoc 2005, 76(1):4–8.

Schmiedt C, Kellum H, Legendre AM, et al. Cardiovascular involvement in 8 dogs with Blastomyces dermatitidis infection. J Vet Intern Med 2006, 20(6):1351–1354.

Yajima T, Knowlton,KU . Viral myocarditis, From the perspective of the virus. Circulation 2009, 119:2615–2624.

Author Larry P. Tilley

Consulting Editors Larry P. Tilley and Francis W.K. Smith, Jr.

Acknowledgment The author and editors acknowledge the prior contribution of Michael B. Lesser.