bovis - Articles
Myocarditis
Synonym(s): Heart, cardiac
Introduction
- Inflammatory changes/necrosis of myocytes.
- Can be focal or diffuse.
- Cause: various:
- Idiopathic
- Viral (eg BVDV, Foot and Mouth Foot and Mouth etc).
- Bacterial (eg Histophilus Somni Histophilus somni infection, Clostridium chauvoei Clostridium spp).
- Toxic (Ionophores used as growth promoters; drug reactions etc).
- Parasitism (eg Neospora Caninum Neospora Caninum can cause myocarditis, along with other pathology, in the fetus).
- Penetrating foreign body: such as a wire from the reticulum leading to bacterial Myocarditis
Traumatic reticulitis. 
- Signs: vary depending upon underlying etiology: Dysrhythmias Dysrhythmias frequently seen, reduced exercise tolerance, reduced milk yield, poor growth rates , malaise, Congestive heart failure Congestive heart failure, Sudden death.
- Diagnosis: very difficult - no pathognomic signs; echocardiography.
- Treatment: in most cases of extensive myocardial damage or necrosis, treatment is ineffectual and cost prohibitive once clinical signs are apparent.
- Prognosis: guarded.
Cost considerations
- Reduced milk yield.
- Reduced growth rates.
- Abortion secondary to myocarditis.
- In the case of eosinophillic myositis in conjunction with eosinophillic myocarditis (EM) - carcass trimming, sometimes carcass condemnation.
- In the case of bacterial myocarditis - if sepsis are also present: carcass condemnation.
Pathogenesis
Etiology
- Possible relationship between parasitism and eosinophillic myocarditis, but definitive link not proven. The exact cause of EM isn't known.
- Bacterial myocarditis can originate from hematogenous spread, but a penetrating foreign body (such as a wire) from the reticulum is a common cause.
- Reactions to drugs and ingested toxins can precipitate myocarditis.
Predisposing factors
General
- Immunosuppression.
- Debility.
Specific
- Exposure to infectious agent or use of myocardiotoxic substances.
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.
- Results in cardiac dysfunction.
- Infection may arise locally or be spread from distant sites, e.g. uterus, lung etc.
- Infection/toxicity → toxin (local or blood borne)/immune-complex/direct invasion → vasculitis/myocyte damage → myocardial inflammation → cardiac dysfunction = dysrhythmias/CHF.
- Often concurrent signs of sepsis and SIRS SIRS.
- Damage, inflammation +/- necrosis of myocardium and conduction tissues → systolic and diastolic dysfunction and dysrhythmias Dysrhythmias.
Acute
- Direct damage to myocytes or ischemia due to coronary artery occlusion → myocardial inflammation and reduced myocardial contractile efficiency.
- Death/inflammation of myocytes → increased automaticity and provokes dysrhythmia.
Chronic
- Replacement fibrosis and loss of contractile tissue cause progressive systolic and diastolic dysfunction of the myocardium resulting in global compromise of cardiac function and signs of low output heart failure.
- Ultimately the cardiac remodelling results in a hypocontractile dilated ventricle that mimics dilated cardiomyopathy in other species.
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.
- Wouda W, Snoep J J, Dubey J P (2006) Eosinophilic Myositis due to Sarcocystis hominis in a Beef Cow. J Comp Pathol 135 (4), 249–253 PubMed.
- Wessels J, Wessels M E (2005) Histophilus somni myocarditis in a beef rearing calf in the United Kingdom. Vet Rec 157 (14) 420-1 PubMed.
- Dubey J P, Miller S, Lindsay D S & Topper M J (1990) Neospora caninum-associated myocarditis and encephalitis in an aborted calf. J Vet Diagn Invest 2 (1), 66-69.
- Jaspers R (1962) Bovine Eosinophillic Myocarditis. Iowa State University Veterinarian 25 (2), 7.