Dilated Cardiomyopathy

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Chapter 26

Dilated Cardiomyopathy

1. What is the definition of dilated cardiomyopathy?

    Dilated cardiomyopathy (DCM) refers to a spectrum of heterogeneous myocardial disorders characterized by ventricular dilation and depressed myocardial contractility in the absence of abnormal loading conditions (e.g., hypertension or valvular heart disease) or ischemic heart disease sufficient to cause global systolic impairment. Thus, DCM can be envisioned as the final common pathway for myriad cardiac disorders that either damage the heart muscle or, alternatively, disrupt the ability of the myocardium to generate force and subsequently cause chamber dilation.

    In practice and clinical trials, DCM is used interchangeably with nonischemic cardiomyopathy (NICM), although the latter includes systolic heart failure (heart failure) related to hypertension or valvular disease.

2. How prevalent is DCM?

    The incidence of DCM is 5 to 8 per 100,000 persons, whereas the prevalence is 36 per 100,000. DCM accounts for 10,000 deaths annually and represents approximately 30% to 40% of heart failure cases (as defined by NICM). African Americans are three times more likely to develop DCM than whites, and more likely to die from DCM compared with age-matched whites.

3. How does DCM present?

    The presenting features of DCM are typical of heart failure and include symptoms of left ventricular (LV) failure, including progressive exertional dyspnea, fatigue, weakness, diminished exercise capacity, orthopnea, paroxysmal nocturnal dyspnea, and nocturnal cough. Abdominal distension, right upper quadrant abdominal pain, early satiety, postprandial fullness, and nausea are seen with the development of right-sided heart failure. In advanced heart failure, cardiac cachexia may develop. Approximately 4% to 13% of the patients with DCM will present with asymptomatic LV dysfunction and LV dilation.

4. What kind of diagnostic studies should be carried out for DCM?

    The diagnostic evaluation is similar to those with ischemic heart failure and should include routine assessment of serum electrolytes, liver function tests, complete blood cell count, cardiac enzymes, serum natriuretic peptide levels (B-type natriuretic peptide [BNP] or N-terminal prohormone of BNP [NT-proBNP]), chest radiograph, electrocardiogram, and assessment of LV function by echocardiography or radionuclide imaging.

    Echocardiography typically shows four-chamber dilation, wall thinning, global hypokinesis, and left ventricular ejection fraction (LVEF) less than 35% to 40%. LV apical thrombi can be identified in up to 40% of patients with DCM. Tricuspid and mitral regurgitation may be present as a result of annular dilation and altered LV geometry. Doppler mitral inflow patterns may reveal elevated filling pressures.

    Multigated radionuclide angiocardiography (MUGA) may be used to assess LV systolic function in those with poor echocardiographic windows. Compared with echo assessment of LVEF, MUGA may have less interobserver and intertest variability. Thallium-201 myocardial scintigraphy is not a reliable technique for differentiating patients with ischemic cardiomyopathy (ICM) from those with DCM, as patients with DCM may have both reversible and fixed perfusion abnormalities related to the presence of myocardial fibrosis, although a completely normal scan (without reversible or fixed defects) would favor the diagnosis of NICM.

    Cardiac catheterization may be performed if symptoms suggestive of ischemia are present or if coronary artery disease is strongly suspected. Catheterization in DCM generally shows normal coronary arteries or mild, nonobstructive, isolated atherosclerotic lesions that are insufficient to explain the extent of cardiomyopathy.

    Endomyocardial biopsy may be performed if and only if a specific diagnosis is suspected in which specific therapy may be efficacious upon establishment of diagnosis (see Chapter 23 on endomyocardial biopsy).

5. What is the natural history of DCM?

    The natural history of DCM depends on the underlying cause. Generally, symptomatic patients have a 25% mortality at 1 year and 50% mortality at 5 years. The prognosis in those with asymptomatic LV dysfunction is less clear. Pump failure accounts for approximately 70% of deaths, whereas sudden cardiac death accounts for approximately 30%.

    Approximately 25% of symptomatic DCM patients will improve spontaneously. Idiopathic DCM has a lower total mortality compared with ischemic cardiomyopathy, although the risk of sudden death may be higher.

6. What are the prognostic features of DCM?

    Many of the prognostic features are similar to those in ischemic cardiomyopathy, including age, LVEF, New York Heart Association (NYHA) class, lack of heart rate variability, elevated levels of neurohormones, and elevated markers of myocardial cell death. However, certain causes of DCM carry a more favorable prognosis and are potentially reversible—for example, cardiomyopathy associated with alcohol, peripartum, trastuzumab, or tachycardia. Other causes, such as anthracyclines or human immunodeficiency virus (HIV), have a worse prognosis.

7. What are the common causes of DCM?

    The term nonischemic cardiomyopathy may include cardiomyopathies commonly caused by hypertension or valvular heart disease, which are not conventionally accepted under the definition of DCM. Causes for DCM include genetic causes (familial cardiomyopathies), toxins (alcohol, cocaine, chemotherapy such as anthracycline), infection (such as Coxsackie virus, HIV, Trypanosoma cruzi), inflammatory disorders (such as collagen vascular disease, hypersensitivity myocarditis), nutritional causes (such as thiamine deficiency), pregnancy, endocrine causes (such as diabetes, hyperthyroidism), tachycardia, and stress-induced (tako-tsubo) cardiomyopathy.

8. What are the features of alcohol-induced cardiomyopathy?

    Alcohol-induced cardiomyopathy is said to occur when cardiomyopathy is noted in a heavy drinker in the absence of other causes (i.e., by exclusion). Alcoholic patients consuming more than 90 g of alcohol a day (approximately 7 to 8 standard drinks per day) for more than 5 years are at risk for this entity. Symptoms may develop with continued drinking. Approximately 20% of subjects with excessive drinking may demonstrate clinical heart failure. The typical patient is a man 30 to 55 years old who has been a heavy alcohol consumer for 10 years. Women may be more susceptible to the cardiodepressive effects of alcohol. Death rates are higher in African Americans (compared with whites). Abstinence may partially or completely reverse the cardiomyopathy. Overall prognosis remains poor, with a mortality of 40% to 50% at 3 to 6 years without abstinence.

9. What are the features of cocaine-induced cardiomyopathy?

    Approximately 4% to 18% of cocaine users have depressed LV function. Cardiac catheterization reveals normal or mildly diseased coronary arteries, insufficient to explain the extent of myocardial dysfunction. Abstinence may lead to reversal.

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