Etiology

• Bacterial, viral, fungal or parasitic infection.
• Chlamydia, Corynebacterium, Salmonella Salmonellosis and Mycobacterium spp Mycobacteriosis have been associated with myocarditis in reptiles.
• Atadenovirus Atadenovirus infection is reported in lizards and arenavirus is reported in snakes with myocarditis.
• Systemic inflammatory disease, such as sepsis, can result in reduced myocardial function.
• Immune suppression.
• Toxic, eg doxorubicin, cardiac glycosides.
• Arrhythmia-induced, eg tachyarrhythmias.
• Nutritional (reported in some species, poor evidence in exotics).
• Severe systemic disease, eg endocrinopathies.
• Trauma.
• Envenomation.

Predisposing factors

General

• Immunosuppression, eg related to inadequate husbandry (lack of appropriate temperature gradient, humidity, UVB provision) in reptiles Chelonia husbandry Lizard husbandry Snake husbandry.
• Debilitation.

Specific

• Exposure to infectious agents.

Pathophysiology

• Acute or chronic inflammation of the myocardium secondary to the conditions listed in the etiology section above.
• Inflammation can lead to supraventricular and/or ventricular arrhythmias secondary to abnormal automaticity, triggered activity, increased normal automaticity or re-entry (disease dependent).
• Inflammation can result in decreased myocardial contractility, leading to eccentric hypertrophy (in some species, reports also describe concentric hypertrophy due to the accumulation of inflammatory cells, non-cardiomyocyte cell populations and edema in the tissue).
• In systemic diseases, a sympathetic storm, ie an increased heart rate and free radical release, can lead to arrhythmias and damage to the myocardium, which in turn leads to inflammation.
• Infectious agents can cause sympathetic disease, as aforementioned, or they can directly affect the myocardium, resulting in immune-mediated inflammation of the tissues.
• May be acute or chronic.
• Infection may arise locally or spread from distant sites.

Timecourse

• Acute = days.
• Chronic = months, often secondary to other diseases such as tachy-cardiomyopathies.