Viral Myocarditis

Myocarditis is inflammation of the myocardium (heart muscle) that can result from infectious, autoimmune, or toxic causes, with viral infection being a common infectious cause. Enteroviruses, including Coxsackie B, are important viral causes. The virus can injure cardiomyocytes directly, and the immune response that follows can extend the damage to otherwise uninfected cells. That combination explains why symptoms may continue or worsen after the initial viral illness has improved. Inflammation and myocardial cell injury reduce contractility, so the ventricle may eject less blood with each beat. The inflamed muscle may also become less compliant, impairing filling. Reduced forward flow produces fatigue, weakness, exertional dyspnea, and sometimes cool extremities or reduced urine output. Rising filling pressures cause orthopnea, pulmonary crackles, jugular venous distension, and peripheral oedema. Inflammation can involve the cardiac conduction system as well as the muscle itself. The patient may develop ectopic beats, atrioventricular block, supraventricular arrhythmias, or dangerous ventricular tachyarrhythmias. A heart that is both inflamed and electrically unstable is particularly vulnerable during exertion. This is why activity restriction is a treatment measure, not simply advice to “take...