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Dilated cardiomyopathy (DCM) is myocardial dysfunction causing heart failure in which ventricular dilation and systolic dysfunction predominate. Symptoms include dyspnea, fatigue, and peripheral edema. Diagnosis is clinical and by chest x-ray, natriuretic peptides, echocardiography, and MRI. Treatment is directed at the cause. If heart failure is progressive and severe, cardiac resynchronization therapy, implantable cardioverter-defibrillator, repair of moderate to severe valvular regurgitation, or heart transplantation may be needed.
In some patients, DCM is believed to start with acute myocarditis (probably viral in most cases), followed by a variable latent phase, a phase with diffuse necrosis of myocardial myocytes (due to an autoimmune reaction to virus-altered myocytes), and chronic fibrosis. Regardless of the cause, the myocardium dilates, thins, and hypertrophies in compensation (see see Figure: Forms of cardiomyopathy.), often leading to functional mitral or tricuspid regurgitation and atrial dilation.
The disorder affects both ventricles in most patients, only the left ventricle (LV) in a few (unless the cause is ischemia), and only the right ventricle (RV) rarely.
Mural thrombi frequently form once chamber dilation is significant, especially during the acute myocarditis phase. Cardiac arrhythmias often complicate the acute myocarditis and late chronic dilated phases as may atrioventricular (AV) block. Atrial fibrillation commonly occurs as the left atrium dilates.
DCM has many known and probably many unidentified causes (see Causes of Dilated Cardiomyopathy). The most common cause in temperate zones is diffuse coronary artery disease (CAD) with diffuse ischemic myopathy. More than 20 viruses can cause DCM; in temperate zones, coxsackievirus B is most common. In Central and South America, Chagas disease due to Trypanosoma cruzi is the most common infectious cause. DCM is becoming increasingly common among patients with HIV infection. Other causes include toxoplasmosis, thyrotoxicosis, and beriberi. Many toxic substances, particularly alcohol, various organic solvents, and certain chemotherapeutic drugs (eg, doxorubicin, trastuzumab), damage the heart.
Sudden emotional stress and other hyperadrenergic states can trigger acute DCM that is typically reversible (as is that caused by prolonged episodes of tachycardia). An example is acute apical ballooning cardiomyopathy (takotsubo cardiomyopathy). In this disorder, usually the apex and occasionally other segments of the LV is affected, causing regional wall dysfunction and sometimes focal dilation (ballooning).
Genetic factors play a role in 20 to 35% of cases; several genes and loci have been implicated.
Causes of Dilated Cardiomyopathy
Onset is usually gradual except in acute myocarditis, acute apical ballooning cardiomyopathy, and tachyarrhythmia-induced myopathy. Symptoms depend on which ventricle is affected. LV dysfunction causes exertional dyspnea and fatigue due to elevated LV diastolic pressure and low cardiac output. RV failure causes peripheral edema and neck vein distention. Infrequently the RV is predominantly affected in younger patients, and atrial arrhythmias and sudden death due to malignant ventricular tachyarrhythmias are typical. About 25% of all patients with DCM have atypical chest pain.
Diagnosis is by history, physical examination, and exclusion of other common causes of ventricular failure (eg, systemic hypertension, primary valvular disorders, MI— Diagnosis and Treatment of Cardiomyopathies). Thus, chest x-ray, ECG, echocardiography, and, more recently, cardiac MRI are required. If acute symptoms or chest pain is present, serum cardiac markers are measured; although typically indicative of coronary ischemia, troponin is often elevated in heart failure, especially if renal function is decreased. Serum natriuretic peptide levels are typically elevated when heart failure is present. Specific causes suspected clinically are diagnosed (see elsewhere in The Manual). If no specific cause is clinically apparent, serum ferritin and iron-binding capacity and thyroid-stimulating hormone levels are measured. Serologic tests for Toxoplasma, T. cruzi, coxsackievirus, and echovirus may be done in appropriate cases.
Chest x-ray shows cardiomegaly, usually of all chambers. Pleural effusion, particularly on the right, often accompanies increased pulmonary venous pressure and interstitial edema.
The ECG may show sinus tachycardia and nonspecific ST-segment depression with low voltage or inverted T waves. Sometimes pathologic Q waves are present in the precordial leads, simulating previous MI. Left bundle branch block and atrial fibrillation are common.
Echocardiography shows dilated, hypokinetic cardiac chambers and rules out primary valvular disorders. Segmental wall motion abnormalities, typical of MI, can also occur in DCM because the process may be patchy. Echocardiography may also show a mural thrombus.
Cardiac MRI is increasingly done and is useful in providing detailed imaging of myocardial structure and function. MRI may show abnormal myocardial tissue texture or scarring pattern, which is diagnostic.
Positron-emission tomography has been shown to be sensitive for diagnosing cardiac sarcoidosis.
Coronary angiography is required when the diagnosis is in doubt after noninvasive tests, particularly for patients with chest pain or several cardiovascular risk factors or for elderly patients, who are more likely to have CAD. However, nonobstructive coronary artery lesions detected by angiography may not be the cause of DCM. Either ventricle can be biopsied during catheterization, but biopsy is not usually done because the yield can be low, the disease process can be patchy, and results may not change treatment.
Prognosis generally has been poor, although prognosis has improved with current management regimens (eg, use of ß-blockers). About 20% die in the first year and then about 10%/yr thereafter; about 40 to 50% of deaths are sudden, due to a malignant arrhythmia or an embolic event. Prognosis is better if compensatory hypertrophy preserves ventricular wall thickness and is worse if ventricular walls thin markedly and the ventricle dilates.
Treatable primary causes (eg, toxoplasmosis, hemochromatosis, thyrotoxicosis, beriberi) are corrected. Otherwise, treatment is the same as for heart failure (see Heart Failure : Treatment): ACE inhibitors, β-blockers, aldosterone receptor blockers, angiotensin II receptor blockers, diuretics, digoxin, and nitrates. Corticosteroids, azathioprine, and equine antithymocyte globulin are no longer used; although they may shorten the acute phase of certain inflammatory myocarditic myopathies (eg, acute postviral or sarcoid myocarditis), they do not improve long-term outcome. Antivirals are not helpful. Colchicine may help reduce acute phase inflammation in viral and other inflammatory peri(myo)carditis.
Because mural thrombi may form, prophylactic oral antithrombotics (see Deep Venous Thrombosis (DVT) : Anticoagulants) are often given to help prevent systemic or pulmonary emboli. However, a recent, large randomized trial comparing warfarin to aspirin showed that warfarin reduced risk of ischemic stroke but was also associated with higher risk of bleeding. The decision to give warfarin or aspirin depends on individual patient characteristics. Warfarin can be considered in patients with a previous cerebrovascular embolism, those with acute severe myocarditis, and some with severe LV dilation.
Aggressive treatment of heart failure reduces risk of arrhythmia, but significant cardiac arrhythmias may be treated with antiarrhythmic drugs. Permanent pacemakers may be required if AV block occurs during the chronic dilated phase. However, AV block during acute myocarditis often resolves, so permanent pacemakers are usually not needed. If patients have a widened QRS interval with a low LV ejection fraction and severe symptoms despite optimized medical treatment, CRT (see Cardiac Resynchronization Therapy) should be considered. An implantable cardioverter-defibrillator may be used to prevent death due to a sudden arrhythmia.
Because prognosis may be poor, patients with DCM may become candidates for heart transplantation. Selection criteria include absence of associated systemic disorders and psychologic disorders, and high, irreversible pulmonary vascular resistance; because donor hearts are scarce, younger patients (usually< 60) are given higher priority.
In dilated cardiomyopathy, the myocardium dilates, thins, and hypertrophies.
Many cases are caused by diffuse ischemia or infection (commonly viral); sometimes a toxin, metabolic or genetic factor, or connective tissue disorder is involved.
Do chest x-ray, ECG, echocardiography, and cardiac MRI to evaluate extent of disease and look for other causes of heart failure, if appropriate.
Treat primary cause if possible and use standard heart failure treatment measures (eg, ACE inhibitors, β-blockers, aldosterone receptor blockers, angiotensin II receptor blockers, diuretics, digoxin, nitrates, implantable cardioverter-defibrillator, and/or cardiac resynchronization therapy).
Consider using oral antithrombotics in patients with previous cerebrovascular embolism, acute severe myocarditis, or severe LV dilation.
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