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Infectious disease and microbiology – Myocarditis
Myocarditis is an inflammatory condition of the heart muscle (myocardium) that can result from a wide range of infectious agents, immune-mediated mechanisms, or external toxins. It may occur due to direct infection of cardiac tissue or from an immune response in which antibodies cross-react with myocardial cells, leading to damage. Although relatively uncommon, with an estimated incidence of 1–10 cases per 100,000 individuals, myocarditis is clinically significant because it contributes to up to 12% of sudden cardiac deaths in adolescents and young adults, affecting young males. Its true prevalence is difficult to determine because presentations range from mild, self-limited illness to severe heart failure or sudden death.
The disease is associated with numerous infectious causes, most commonly viral pathogens such as enteroviruses (especially Coxsackie B), adenovirus, influenza, cytomegalovirus, Epstein-Barr virus, HIV, and others. Bacterial, rickettsial, spirochetal, fungal, protozoal, and parasitic infections may also lead to myocarditis. Notably, Trypanosoma cruzi (Chagas disease) and HIV are important contributors in certain populations. Noninfectious triggers such as toxins, drugs, and systemic inflammatory diseases can also play a role. Immunocompromised individuals are at increased risk, and vaccination against viral pathogens may help reduce incidence.
Pathophysiologically, myocardial injury results from a combination of direct cytotoxic effects of pathogens, immune-mediated inflammation, cytokine release (e.g., tumor necrosis factor-alpha), and apoptosis of cardiac cells, all of which impair cardiac function.
Clinically, patients often report a recent viral-like illness with fever, malaise, or respiratory symptoms, followed by chest pain, palpitations, shortness of breath, or syncope. In some cases, myocarditis mimics acute myocardial infarction, while in others it presents later as chronic heart failure. Physical examination may reveal tachycardia, arrhythmias, signs of heart failure, or an S3 gallop, along with systemic features depending on the underlying cause.
Diagnosis involves a combination of laboratory testing, imaging, and sometimes biopsy. Laboratory findings may include leukocytosis, elevated inflammatory markers, and increased cardiac enzymes such as troponin. Imaging studies—especially echocardiography and cardiac MRI—help assess cardiac function and inflammation. Electrocardiography often shows nonspecific changes or conduction abnormalities. The gold standard for diagnosis is endomyocardial biopsy, which demonstrates inflammatory infiltration and myocardial necrosis, although it carries procedural risks and may yield false negatives.
Management is largely supportive, focusing on treatment of heart failure with medications such as diuretics, ACE inhibitors, and beta-blockers. Specific antimicrobial or antiviral therapy is used when an identifiable cause is present. In severe cases, advanced supportive measures such as ventricular assist devices or extracorporeal membrane oxygenation may be required, and cardiac transplantation may be considered in refractory cases. Adjunctive therapies such as intravenous immunoglobulin or immunosuppressive agents may be used selectively.
Follow-up care includes gradual rehabilitation, serial cardiac monitoring, and repeat imaging, with restrictions on physical activity during recovery. Long-term outcomes vary: some patients recover completely, while others develop complications such as dilated cardiomyopathy, arrhythmias, heart block, or cardiogenic shock. Early recognition and appropriate management are essential to improve prognosis and reduce the risk of serious complications, including sudden cardiac death.
Myocarditis is an inflammatory condition of the heart muscle (myocardium) that can result from a wide range of infectious agents, immune-mediated mechanisms, or external toxins. It may occur due to direct infection of cardiac tissue or from an immune response in which antibodies cross-react with myocardial cells, leading to damage. Although relatively uncommon, with an estimated incidence of 1–10 cases per 100,000 individuals, myocarditis is clinically significant because it contributes to up to 12% of sudden cardiac deaths in adolescents and young adults, affecting young males. Its true prevalence is difficult to determine because presentations range from mild, self-limited illness to severe heart failure or sudden death.
The disease is associated with numerous infectious causes, most commonly viral pathogens such as enteroviruses (especially Coxsackie B), adenovirus, influenza, cytomegalovirus, Epstein-Barr virus, HIV, and others. Bacterial, rickettsial, spirochetal, fungal, protozoal, and parasitic infections may also lead to myocarditis. Notably, Trypanosoma cruzi (Chagas disease) and HIV are important contributors in certain populations. Noninfectious triggers such as toxins, drugs, and systemic inflammatory diseases can also play a role. Immunocompromised individuals are at increased risk, and vaccination against viral pathogens may help reduce incidence.
Pathophysiologically, myocardial injury results from a combination of direct cytotoxic effects of pathogens, immune-mediated inflammation, cytokine release (e.g., tumor necrosis factor-alpha), and apoptosis of cardiac cells, all of which impair cardiac function.
Clinically, patients often report a recent viral-like illness with fever, malaise, or respiratory symptoms, followed by chest pain, palpitations, shortness of breath, or syncope. In some cases, myocarditis mimics acute myocardial infarction, while in others it presents later as chronic heart failure. Physical examination may reveal tachycardia, arrhythmias, signs of heart failure, or an S3 gallop, along with systemic features depending on the underlying cause.
Diagnosis involves a combination of laboratory testing, imaging, and sometimes biopsy. Laboratory findings may include leukocytosis, elevated inflammatory markers, and increased cardiac enzymes such as troponin. Imaging studies—especially echocardiography and cardiac MRI—help assess cardiac function and inflammation. Electrocardiography often shows nonspecific changes or conduction abnormalities. The gold standard for diagnosis is endomyocardial biopsy, which demonstrates inflammatory infiltration and myocardial necrosis, although it carries procedural risks and may yield false negatives.
Management is largely supportive, focusing on treatment of heart failure with medications such as diuretics, ACE inhibitors, and beta-blockers. Specific antimicrobial or antiviral therapy is used when an identifiable cause is present. In severe cases, advanced supportive measures such as ventricular assist devices or extracorporeal membrane oxygenation may be required, and cardiac transplantation may be considered in refractory cases. Adjunctive therapies such as intravenous immunoglobulin or immunosuppressive agents may be used selectively.
Follow-up care includes gradual rehabilitation, serial cardiac monitoring, and repeat imaging, with restrictions on physical activity during recovery. Long-term outcomes vary: some patients recover completely, while others develop complications such as dilated cardiomyopathy, arrhythmias, heart block, or cardiogenic shock. Early recognition and appropriate management are essential to improve prognosis and reduce the risk of serious complications, including sudden cardiac death.
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