Cardiac complications include structural and functional changes to the heart. Some of these cardiovascular changes are mild and are reversible with treatment, while others may be life-threatening. Cardiac complications can include arrhythmias, abnormally slow heart beat, low blood pressure, decreased size of the heart muscle, reduced heart volume, mitral valve prolapse, myocardial fibrosis, and pericardial effusion.Abnormalities in conduction and repolarization of the heart that can result from anorexia nervosa include QT prolongation, increased QT dispersion, conduction delays,  and junctional escape rhythms. Electrolyte abnormalities, particularly hypokalemia and hypomagnesemia, can cause anomalies in the electrical activity of the heart, and result in life-threatening arrhythmias. Hypokalemia most commonly results in patients with anorexia when restricting is accompanied by purging (induced vomiting or laxative use). Hypotension (low blood pressure) is common, and symptoms include fatigue and weakness. Orthostatic hypotension, a marked decrease in blood pressure when standing from a supine position, may also occur. Symptoms include lightheadedness upon standing, weakness, and cognitive impairment, and may result in fainting or near-fainting. Orthostasis in anorexia nervosa indicates worsening cardiac function and may indicate a need for hospitalization. Hypotension and orthostasis generally resolve upon recovery to a normal weight. The weight loss in anorexia nervosa also causes atrophy of cardiac muscle. This leads to decreased ability to pump blood, a reduction in the ability to sustain exercise, a diminished ability to increase blood pressure in response to exercise, and a subjective feeling of fatigue.Some individuals may also have a decrease in cardiac contractility.
In extreme cases, patients with anorexia nervosa who continually refuse significant dietary intake and weight restoration interventions, and are declared incompetent to make decisions by a psychiatrist, may be fed by force under restraint via nasogastric tube after asking their parents or proxies to make the decision for them.The cause of anorexia is currently unknown. There appear to be some genetic components with identical twins more often affected than fraternal twins. Cultural factors also appear to play a role, with societies that value thinness having higher rates of the disease. Additionally, it occurs more commonly among those involved in activities that value thinness, such as high-level athletics, modeling, and dancing. Anorexia often begins following a major life-change or stress-inducing event. The diagnosis requires a significantly low weight and the severity of disease is based on body mass index (BMI) in adults with mild disease having a BMI of greater than 17, moderate a BMI of 16 to 17, severe a BMI of 15 to 16, and extreme a BMI less than 15. In children, a BMI for age percentile of less than the 5th percentile is often used.Treatment of anorexia involves restoring the patient back to a healthy weight, treating their underlying psychological problems, and addressing behaviors that promote the problem. While medications do not help with weight gain, they may be used to help with associated anxiety or depression.