Dilated Cardiomyopathy Workup

Updated: Jan 20, 2017
  • Author: Vinh Q Nguyen, MD; Chief Editor: Henry H Ooi, MD, MRCPI  more...
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Workup

Approach Considerations

The workup in a patient with suspected cardiomyopathy may include the following:

  • Complete blood count
  • Comprehensive metabolic panel
  • Thyroid function tests
  • Iron studies
  • Cardiac biomarkers
  • B-type natriuretic peptide assay
  • Chest radiography
  • Echocardiography
  • Cardiac magnetic resonance imaging (MRI)
  • Electrocardiography (ECG)
  • Endocardial biopsy
  • Cardiac catherization

In addition, a urine toxicology screen is used to detect drugs associated with risk for dilated cardiomyopathy, including cocaine and methamphetamine.

Endomyocardial biopsy has limited usefulness in the evaluation of dilated cardiomyopathy. However, it may be helpful in diagnosing myocarditis, connective tissue disorders, and amyloidosis.

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CBC Count and Metabolic Panel

The principal use of the complete blood cell (CBC) count in these patients is to document anemia. Anemia can be associated with a high-output state.

Hyponatremia signifies a poor prognosis. An elevated creatinine level may represent a primary or drug-related etiology (eg, hypovolemia, azotemia from ACE inhibitors). Contraction alkalosis can be observed secondary to diuretic therapy. Magnesium levels should be closely followed because low levels may cause chronic hypokalemia by dependent potassium uptake.

Liver function test results can be elevated. Possible causes in these patients include one or more of the following:

  • Alcoholic disease
  • Hemochromatosis
  • Hepatic congestion (nutmeg liver)
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Cardiac Biomarkers

Cardiac enzymes are useful for assessing acute or recent myocardial injury. Serum markers for myocardial necrosis (eg, troponin, creatine kinase, creatine kinase-MB) may be acutely elevated in persons with myocarditis. Levels are markedly elevated in persons with muscular dystrophy.

Elevated biomarker levels may indicate acute coronary syndrome, which should be considered as a potential etiology for acute decompensation in a patient with a history of heart failure. Further, while the precise role of cardiac biomarkers is still being defined, there is evidence that patients who present with elevated markers experience more severe heart failure and higher mortality. [76, 77]

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B-Type Natriuretic Peptide

B-type natriuretic peptide (BNP) assays help monitor the presence and severity of fluid overload. Changes in BNP level can reflect response to treatment. A low level of BNP is helpful in ruling out the condition.

In one study, a serum BNP below 100 pg/mL proved useful in excluding heart failure as a cause of dyspnea in emergency department (ED) patients. [78] A number of studies have correlated BNP or NT-proBNP with a worse prognosis.

Tsutamoto et al found that plasma levels of BNP may be a better prognostic indicator of mortality in patients with chronic heart failure than atrial natriuretic peptide (ANP) and is able to provide prognostic information independent of other poor prognostic variables. [79] In their study of 85 patients with chronic heart failure (left ventricular ejection fraction [LVEF] <45%) who were followed for 2 years, the nonsurvivors' (n = 25) BNP levels were 436 ± 83 pg/mL as compared to that of the survivors (n = 60), 89 ± 15 pg/mL. Of note, only 25 patients total were on beta blockers. [79]

In the PARADIGM-HF trial (Prospective comparison of ARNI with ACEI to Determine Impact on Global Mortality and morbidity in Heart Failure), patients with heart failure and reduced LVEF who received sacubitril/valsartan had lower NT-proBNP levels after 12 weeks (from 783 pg/mL to 605 pg/mL) compared to patients on valsartan alone (from 862 pg/mL to 835 pg/mL). [80]  The decreased in NT-proBNP levels were associated with improved mortality (13.3% vs 16.5%, respectively).

In an analysis of data from 1215 patients with systolic heart failure to determine the utility of 5 predictors of mortality—blood urea nitrogen (BUN), BNP, peak VO2 (oxygen consumption), systolic blood pressure (SBP), and pulmonary capillary wedge pressure (PCWP)—BNP was the strongest predictor for death, urgent transplantation, and all-cause mortality in the 2-year follow-up period. [81] The C-statistic (concordance statistic; measures the predictive accuracy of a logistic regression model) for BNP was 0.756 (ie, a good model). On multivariate analysis of all-cause mortality, patients with BNP levels above 579 pg/mL had an odds ratio of 4.4. The 2-year survival for those with BNP levels over 579 pg/mL was 44% compared to 82% for those with BNP levels below 579 pg/mL. [81]

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Imaging Studies

Chest radiography

Assess for enlargement and configuration of the cardiac silhouette. A study investigating the specificity and sensitivity of physical and laboratory findings in patients with dyspnea in the emergency department (ED) suggests that cardiomegaly is one of the most sensitive and specific signs in diagnosing cardiomyopathies. The absence of cardiomegaly on chest radiographs decreases the likelihood of heart failure. Remember that patients with left ventricular hypertrophy and pericardial effusion can also present with an enlarged cardiac silhouette.

Pulmonary vascular congestion may be observed. Hilar vessels may appear more concave, with prominent vasculature of the upper lung fields. Kerley B lines may be present. Pleural effusion usually occurs first on the right side, but it can be bilateral. Abnormal calcifications may be valvular, atherosclerotic, or pericardial in nature. Congenital malformations may be noted. The presence of pulmonary vascular congestion and interstitial edema on chest radiograph increases the likelihood of acute decompensated heart failure about 12-fold.

Echocardiography

Echocardiography has become one of the most useful and most efficient diagnostic modalities in attaining a diagnosis and classification of cardiomyopathy. Echocardiography may be indicated in the ED when a patient has findings suggestive of failure (eg, jugular venous distention) but the diagnosis is unclear.

In this setting, the differential diagnosis may include pulmonary embolism or cardiac tamponade. On echocardiography, secondary findings associated with pulmonary embolism such as right ventricular distention or pericardial effusion with tamponade may be seen. Pericardial effusion can be easily excluded or characterized using this imaging modality.

Different forms of echocardiography offer different information. Two-dimensional echocardiography allows for assessment of overall function.

M-mode assists in measurement of chamber sizes (end-diastolic left ventricular dimensions are usually greater than 65 mm in patients with dilated cardiomyopathy) and wall thickness. Hypertrophy is defined as and LV mass index greater than 115 g/m2 in men, or over 95 g/m2 in women. Doppler echocardiography facilitates the measurement and assessment of flow and valvular pathologies. It also allows for measurements of diastolic and systolic dynamics.

The physician must assess the E wave–to–A wave ratio (E/A) when evaluating left ventricular filling and pulmonary venous flow by Doppler echocardiography during left atrial filling. This provides important information on diastolic function and left atrial pressure. For example, a pattern with an E:A ratio above 2:1 and a short mitral deceleration time suggest a restrictive physiology with elevated left atrial pressure.

Tissue Doppler interrogation measures the velocity of portions of the heart wall, most often the left ventricular basilar annular area. Just as in the blood velocity parameters of E and A amplitudes, similar measurements of wall velocity—E' and A'—are made. Reversal of the E'/A' amplitude signifies likely diastolic dysfunction.

Segmental wall motion abnormalities may suggest an ischemic etiology for the cardiomyopathy. While ischemic cardiomyopathy is a common cause of such abnormalities, however, they can often be observed in association with other forms of cardiomyopathy, as well.

Echocardiography is used to help differentiate dilated cardiomyopathy from restrictive and hypertrophic cardiomyopathy. Dilated chambers and thin walls are the most prominent features of dilated cardiomyopathy.

Magnetic resonance imaging (MRI)

MRI with gadolinium–diethylene-triamine pentaacetic acid (DTPA) has been used to evaluate the extent of mid-wall fibrosis, which may correlate with risk of arrhythmias and failure to respond to treatment. Further investigation is ongoing in the role that subendocardial sparing mid-wall fibrosis plays in the pathogenicity of arrhythmias. In the future, MRI with gadolinium may be used for the risk stratification of patients with dilated cardiomyopathy. [82]

Cardiac computed tomography (CT) scanning

Cardiac CT scanning with angiography (CTA) can be used in the workup of undifferentiated heart failure. Biventricular volume and ejection fraction can be calculated with good correlation to echocardiography. With cine-loop formatting, regional wall motion can be assessed, with the highest accuracy for wall motion subtended by the left anterior descending and left circumflex arteries. [83]

In the assessment of ischemic cardiomyopathy, an Agatston coronary calcium score (CAC) of 0 has 100% specificity in excluding high-risk coronary artery disease (ie, the left main coronary artery, or stenosis of at least 2 major epicardial vessels). [84, 85]  Cardiac CTA has a 98% diagnostic sensitivity and 97% specificity for excluding ischemic cardiomyopathy. [86]

Myocardial perfusion analysis of the coronary arteries is also feasible; however, it has yet to mature to the level of diagnostic accuracy of cardiac MRI.

Finally, anatomic features specific to an inciting disease can be differentiated on CTA, such as infiltrative diseases (heterogeneous attenuation of myocardium), the location of hypertrophic cardiomyopathy, left ventricular noncompaction, arrhythmogenic right ventricular dysplasia, and congenital malformations. [85]

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Electrocardiography

An electrocardiogram (ECG) is helpful in identifying left ventricular enlargement and estimating the other chamber sizes. Atrial fibrillation or premature ventricular complexes are noted. Left ventricular hypertrophy or other chamber enlargement is observed. Conduction delay, particularly left bundle-branch block, can be observed. Varying degrees of atrioventricular block are noted.

An ECG showing atrial fibrillation increases the likelihood of heart failure. The absence of any ECG abnormality decreases the likelihood of heart failure. This is an important screening tool in differentiating ischemic heart disease from dilated cardiomyopathy.

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Right-Sided Heart Catheterization

Right-sided heart catheterization (RHC) can be beneficial in initially determining the volume status of a patient with equivocal clinical signs and symptoms of heart failure. RHC in a patient with dilated cardiomyopathy demonstrates elevated filling pressures (central venous pressure, pulmonary artery wedge pressure, right ventricular end-diastolic pressure) and decreased cardiac output. RHC is also important for assessing pulmonary vascular resistance, mixed venous saturation, and the adequacy of cardiac output in patients who are hemodynamically compromised. 

In restrictive cardiomyopathy, RHC demonstrates a pattern in the ventricular hemodynamic tracing referred to as the "square root sign" or "dip-and-plateau pattern." This pattern is similar to that observed in patients with constrictive pericarditis, but in restrictive cardiomyopathy, the left ventricular end-diastolic pressure generally exceeds the right ventricular end-diastolic pressure by 6 mm Hg or more and the entire diastolic filling period is abnormal, while constrictive pericarditis is associated with normal or increased early filling.

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Endomyocardial Biopsy

In many cases of cardiomyopathy, endomyocardial biopsy is class II (uncertain efficacy and may be controversial) or class III (generally not indicated). The exception to this is in cardiac transplant recipients, in whom routine periodic assessment of transplant rejection is necessary.

Class II indications for endomyocardial biopsy include the following:

  • Recent onset of rapidly deteriorating cardiac function
  • Patients receiving chemotherapy with doxorubicin
  • Patients with systemic diseases with possible cardiac involvement (eg, hemochromatosis, sarcoidosis, amyloidosis, Löffler endocarditis, endomyocardial fibroelastosis)

Evidence does not indicate a benefit for performing myocardial biopsy when evaluating the likelihood of patient survival with current therapies.

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Histologic Findings

Findings may include myocardial injury with inflammatory mediators (eg, macrophage derived, antibody/complement). Physical disruption of myocytes by inflammatory cells, proliferation of interstitial cells, and increased fibrous matrix may also be found.

Lymphocytic myocarditis is the most common finding in human cardiac tissue biopsy specimens. Myocyte necrosis, degeneration, or both with adjacent inflammatory infiltrate may be present. Changes suggestive of coronary artery disease may be present. A predominance of lymphocytes and some monocytes without significant eosinophils may be present. Lymphocytic myocarditis is likely related to viral or other infections.

Eosinophilic myocarditis, sometimes called Löffler or Loeffler myocarditis, is usually due to the effects of a drug allergy. Perivascular infiltrates with eosinophil predominance, lymphocytes, and macrophages may be present. Eosinophilic myocarditis usually occurs with peripheral eosinophilia, rash, and/or fever.

Giant cell myocarditis is a rare condition usually associated with systemic illnesses such as the following:

  • Infections (eg, tuberculosis, endocarditis, fungi, syphilis, leprosy)
  • Rheumatologic illnesses (eg, rheumatoid arthritis, lupus, vasculitides, polymyositis, dermatomyositis)
  • Gastrointestinal conditions (eg, Crohn disease, ulcerative colitis, chronic hepatitis)
  • Autoantibody-associated conditions (eg, myasthenia gravis, Hashimoto thyroiditis)
  • Sarcoidosis

Giant cell myocarditis is often associated with conduction abnormalities and may progress rapidly. Necrotizing or nonnecrotizing granulomas are found, often with eosinophilia. T-cell infiltrates have been documented, and anti-CD3 antibody therapy may be effective. The idiopathic type is most often progressive and may require cardiac transplantation. Patients are usually young and present with heart failure or ventricular arrhythmias.

Peripartum myocarditis may be a variant of lymphocytic myocarditis and worsens during pregnancy. In AIDS-related myocarditis, inflammatory infiltrates are observed in cardiac tissue, usually consisting of CD8+ T lymphocytes.

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Other Tests

Hypothyroidism, hyperthyroidism, and thyroid hormone toxicity are all problems to be considered in the differential diagnosis of cardiomyopathy. For example, thyrotoxicosis is associated with a high-output state that may predispose to dilated cardiomyopathy. Results of thyroid function tests are not usually available to assist in decision making in the ED but may be sent for convenience.

On oxygen consumption testing, an oxygen consumption per minute (VO2) maximum of less than 14 mL/kg/min signifies a poor prognosis. Such patients should be given early consideration to heart transplantation.

A central venous line or pulmonary artery catheter provides a good measure of filling pressures, and the latter can be used to estimate cardiac output. However, neither has been shown to improve outcomes when used in acute decompensated heart failure.

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Staging

Classic staging of heart failure is based on the New York Heart Association (NYHA) system. It may also be classified by the the American College of Cardiology/American Heart Association (ACC/AHA) system, which emphasizes the progressive nature of heart failure, as follows [87] :

  • Stage A (high risk for developing heart failure): hypertension, coronary artery disease, diabetes mellitus, family history of cardiomyopathy
  • Stage B (asymptomatic heart failure): previous myocardial infarction, left ventricular systolic dysfunction, asymptomatic valvular disease
  • Stage C (symptomatic heart failure): structural heart disease, dyspnea, fatigue, reduced exercise tolerance
  • Stage D (refractory end-stage heart failure): marked symptoms at rest despite maximal medical therapy, recurrent hospitalizations
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