Autoimmune myocarditis is an autoimmune disease resulting in damage to the myocardium of the heart. Autoimmune myocarditis is a genetic and rare disease according to the National Institute of Health (NIH). The development of autoimmune diseases is the result of a lack of “self-tolerance” of the immune system of the body. An autoimmune disorder occurs when the body's immune system attacks and destroys healthy body tissue by mistake.
This disorder arises as a consequence of a defective function in immune system regulation and cells that comprise the immune system. Autoimmune myocarditis is an immune system attack on the heart resulting in aggravation and inflammation leading to damage of the myocardium (heart muscles). Generally, the clinical event of inflammation and myocardial damage in both general and autoimmune myocarditis is similar. Therefore, discussion on autoimmune myocarditis regarding symptoms and pathogenesis will be overlapping with myocarditis in general. Myocarditis is commonly regarded as a major public health concern due to sudden heart failures in young adults. Myocarditis was first coined in 1669 when physicians documented inflammation in the heart as a pathologic event. There are a number of factors affecting the development of autoimmunities such as having systemic autoimmune disease, exposures to toxins, or hypersensitivity to medications, and exposure to certain viruses. In virus-induced autoimmune myocarditis, an autoimmune reaction like antigen mimicry may be induced, where viral particles can mimic the body’s own molecules to elicit an antibody-based autoimmune mechanism leading to the self-destruction of the body’s own tissues and organs. A very specific and novel cause of autoimmune myocarditis is immune checkpoint inhibitor (ICI)-induced myocarditis, which is a result of drug therapy in cancers. Unfortunately, both innate and adaptive immune systems of the body are involved in the autoinflammatory processes of autoimmune myocarditis. Among the cardiomyopathies resulting from acute myocarditis, dilated cardiomyopathy or DCM is a clinically severe and fatal disease leading to cardiac arrest. Among the non-infectious myocarditis, there are three diseases namely rare giant cell myocarditis, eosinophilic necrotizing myocarditis, and immune checkpoint inhibitors or ICI-induced myocarditis. The latter is a result of an unchecked immune system and has a high associated rate of mortality. In the U.S., based on inpatient or hospital admitted patient sample data over the course of nine years, a gradual increase in the number of reported cases of myocarditis was observed from 95 per one million in 2005 to 144 per one million in 2014, of which the overall death was 4.43% of inpatients. In addition, past reports on ICI myocarditis, suggests that there may be up to 1–2% of ICI myocarditis with a significant mortality of 30%. While ICI therapy has been hailed as a useful therapy in the treatment of cancers, ICI myocarditis is considered a potential autoimmune side effect. Females are more affected than males.
The etiology of autoimmune myocarditis may be viral or of a non-infectious cause such as the effect of cardiotoxins, hypersensitivity reactions within the body, radiation exposures, and systemic disorders such as systemic lupus erythematosus (SLE) and sarcoidosis. In addition, questions remain regarding the cardiovascular effects associated with severe acute respiratory syndrome related to SARS-CoV-2 infections. There are risk factors specific to the development of autoimmune myocarditis which may be systemic/local primary autoimmunity, viral infection, human leukocyte antigen (HLA) or host susceptibility factor and gender bias, exposure of cryptic antigens, antigen mimicry, and deficient thymic training induction. Symptoms range from chest pain to signs of acute cardiogenic shock. Diagnosis relies on preliminary clinical examination of patients and imaging followed by laboratory tests. Immunosuppressants are recommended therapeutics in autoimmune myocarditis along with other symptomatic treatments. Cardiac transplantation should be postponed in the acute phase of myocardial inflammation but may be considered for hemodynamically unstable patients with myocarditis if most of the intravenous drugs and mechanical assistance fail. Ventricular assist devices and oxygenation assist devices like ECMO may be required to provide medical assistance for cardiac transplant patients or recovery in case of cardiogenic shock. Patients with hemodynamically stable conditions, but having heart failure, should be treated with diuretics, angiotensin-converting enzyme inhibitor or angiotensin receptor blockers, and beta-adrenergic blockers to expel the undesired amount of water and salts from the body (via the urine) leading to lower blood pressure. In persistent heart failure despite the optimal management, additional treatment with aldosterone antagonists should be recommended. In addition, all types of physical activity or exercise should be avoided during myocarditis until full resolution. Specifically, in autoimmune myocarditis with common systemic disorders, high-dose intravenous immunoglobulin (IVIG) as a therapeutic, is a promising option. Proper follow-up should be maintained for every patient.
Written by: Souvik Datta, Ph.D. & Lawrence D. Jones, Ph.D.