Dilated cardiomyopathy overview
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Dilated cardiomyopathy is a condition of the heart that causes dilation and impaired contraction of the left ventricle (or both ventricles). Impaired contraction is defined as a low ejection fraction (< 40%).
The etiology of dilated cardiomyopathy remained elusive for a long time that it was defined by the World Health Organization as a "heart muscle disorder of unknown cause". However, recent research highlighted several genetic mutations that are associated with the condition. Therefore, the more recent definition by the American Heart Association was "a myocardial disorder with mechanical dysfunction, which usually exhibits inappropriate ventricular dilatation, due to a variety of etiologies that frequently are genetic".
Familial traits and mitochondrial inheritance are thought to play a part in the development of idiopathic dilated cardiomyopathy, and the inheritance occurs in an autosomal dominant pattern. Connective tissue disease, and other diseases or toxins that disrupt the tissue of the heart are also implicated in the development of dilated cardiomyopathy.
There are many causes of dilated cardiomyopathy. The most common cause is idiopathic in 50% of cases. The next most common cause is myocarditis which is responsible for 10% of cases. Other common causes include substance abuse, connective tissue disease, pregnancy, medications, nutritional deficiencies, infiltrative diseases and toxins.
Epidemiology and Demographics
Dilated cardiomyopathy is most likely to occur between the ages of 20-60, is three times as likely to occur in males over females, and is 2.5 times more likely to occur in African Americans.
The current guidelines recommend screening for dilated cardiomyopathy in individuals with 2 or 3 family members with primary dilated cardiomyopathy. Screening can be performed using electrocardiograms and echocardiography to measure the size and function of the left ventricle. An underlying genetic mutation in the 40 genes (currently assessed in familial dilated cardiomyopathy genetic testing) can be detected in 30 to 40% of DCM patients.
Natural History, Complications and Prognosis
There are several prognostic indicators when evaluating dilated cardiomyopathy, the most important one being ejection fraction. Complications as a result of dilated cardiomyopathy include heart failure, aortic and mitral valve regurgitation, emboli, edema, arrhythmias and sudden cardiac arrest.
History and Symptoms
Common symptoms in the setting of dilated cardiomyopathy include chest pain, cough, fatigue, loss of appetite, and shortness of breath. A careful history is important in the setting of dilated cardiomyopathy in order to ascertain the etiology of the cardiomyopathy. The patient needs to be evaluated for a history of coronary artery disease, viral prodrome and infections, chemotherapy, HIV risk factors, pregnancy, medications, toxins, and substance abuse.
The majority of dilated cardiomyopathy lab workup is targeted towards detecting the cause (such as thyroid function tests, toxicology screening, and genetic counselling) or assessing the cardiac complications of the condition. Other biomarkers that are under investigation include serum uric acid, Ca-125, soluble ST2, and Growth and differentiation factor-15.
In patients presenting with heart failure, where the etiology of the cardiac dysfunction is unclear, cardiac MRI can be a useful imaging modality. It can be used to distinguish the area of inflammation, to help in the diagnosis of myocarditis, to evaluate patients with suspected infiltrative diseases, and to evaluate dilated cardiomyopathy in the setting of normal coronary arteries.
Echocardiography is the most common imaging finding used to diagnose dilated cardiomyopathy. Findings may include ventricular and atrial dilatation, increased left ventricular mass, a global reduction in systolic function, and focal wall motion abnormalities.
Other Diagnostic Studies
Endomyocardial biopsy has low sensitivy and the findings are also notoriously non-specific. The findings on biopsy usually involve findings of inflammation and specific pathogens are unlikely to be identified. There may be an increased yield to using MRI to target endomyocardial biopsy. Viral titiers (serologies) are often unhelpful and not routinely ordered in clinical practice.
Treatment should focus on correcting the underlying cause of the cardiomyopathy when possible. Treatment is also targeted towards preventing death, and ameliorating the symptoms of heart failure. Medications that have been proven to reduce mortality in patients with systolic heart failure are; ACE inhibitors, beta blockers, angiotensin II receptor blockers, nitrates, and hydralazine. Diuretics and digoxin are used for symptom relief.
There are several surgical options for patients with dilated cardiomyopathy, depending on the severity of heart failure. Implantable cardiac defibrillators have been studied in these patient, and may help in preventing arrhythmias. Cardiac transplantation may be an option for patients with severe heart failure, and a left ventricular assist device, or LVAD, may help to bridge a patient while awaiting transplantation. This device may also be used as a palliative measure, called a "destination LVAD" for patients with end-stage heart failure who are not suitable transplant candidates.