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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 and echocardiography. Treatment is directed at the cause; if progressive and severe, heart transplantation may be needed.
Pathophysiology
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 Fig. 1: Cardiomyopathies: 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 with an ischemic etiology), 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.
Etiology
DCM has many known and probably many unidentified causes (see Table 2: Cardiomyopathies: 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.
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, only the apex 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.
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Table 2
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| Causes of Dilated Cardiomyopathy |
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Cause
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Examples
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Chronic diffuse myocardial ischemia
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Coronary artery disease
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Chronic tachycardia
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Uncontrolled atrial fibrillation
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Infections (acute or chronic)
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Bacterial
Spirochetal
Rickettsial
Viral (including HIV infection)
Fungal
Protozoan
Helminthic
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Granulomatous disorders
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Sarcoidosis
Granulomatous or giant cell myocarditis
Wegener's granulomatosis
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Metabolic disorders
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Nutritional disorders (eg, beriberi, selenium deficiency, carnitine deficiency, kwashiorkor)
Familial storage disorders
Uremia
Hypokalemia
Hypomagnesemia
Hypophosphatemia
Diabetes mellitus
Hyperthyroidism
Hypothyroidism
Pheochromocytoma
Acromegaly
Morbid obesity
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Drugs and toxins
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Ethanol
Cocaine
Anthracyclines
Cobalt
Psychotherapeutic drugs (tricyclic and quadricyclic antidepressants, phenothiazine)
Catecholamines
Cyclophosphamide
Radiation
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Tumors
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Certain endocrinologically active tumors (eg, pheochromocytoma, adrenal, tumors, thyroid tumors)
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Connective tissue disorders
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SLE
Systemic sclerosis
RA
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Genetic abnormality
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Familial disease in 20–30% of patients: autosomal dominant, X-linked, autosomal recessive, or mitochondrial inheritance
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Hereditary neuromuscular and neurologic disorders
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Friedreich's ataxia
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Pregnancy (peripartum period)
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—
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Symptoms and Signs
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
Diagnosis is by history, physical examination, and exclusion of other common causes of ventricular failure (eg, systemic hypertension, primary valvular disorders, MI—see Table 1: Cardiomyopathies: Diagnosis and Treatment of Cardiomyopathies). Thus, chest x-ray, ECG, and echocardiography are required. If acute symptoms or chest pain is present, serum cardiac markers are measured; although typically indicative of coronary ischemia, troponin levels can be elevated in heart failure, especially if renal function is decreased. 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 and 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 is 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. MRI is not routinely done but may be useful when detailed imaging of myocardial structure or function is needed. In cardiomyopathy, MRI may show abnormal myocardial tissue texture.
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
Prognosis generally is 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.
Treatment
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.
Because mural thrombi may form, prophylactic oral anticoagulants (see Peripheral Venous Disorders: Anticoagulants) are often given to help prevent systemic or pulmonary emboli, and a large randomized trial is underway to test whether this approach is effective. Patients with a previous cerebrovascular embolism, those with acute severe myocarditis, and some with severe LV dilation should receive anticoagulants.
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, biventricular pacing should be considered. An implantable cardioverter-defibrillator may be used to prevent sudden arrhythmia-induced death.
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.
Last full review/revision January 2010 by J. Malcolm O. Arnold, MD
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