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Dilated Cardiomyopathy Imaging

Practice Essentials

The World Health Organization (WHO) has defined dilated cardiomyopathy as a condition in which the ventricular chambers exhibit increased diastolic and systolic volume and a low (< 40%) ejection fraction.
In the WHO/International Society and Federation of Cardiology classification, dilated cardiomyopathy in its primary (eg, idiopathic or familial) and secondary forms is the most common cause of the clinical syndrome of chronic heart failure. Dilated cardiomyopathy is the most common form of childhood cardiomyopathy and causes significant morbidity and mortality.

In most cases, dilated cardiomyopathy is progressive, leading to heart failure and death. Without a transplant, survival rates are poor. Continued enlargement of the ventricles leads to a decline in ventricular function, followed by conduction system abnormalities, ventricular arrhythmias, thromboembolism, and heart failure.

The prevalence of heart failure is approximately 1-1.5% in the adult population of Western countries. Dilated cardiomyopathy is associated with a large number of systemic or cardiac diseases, including specific heart muscle diseases (eg, ischemic cardiomyopathy, diabetic cardiomyopathy, alcoholic cardiomyopathy).

Dilated cardiomyopathy constitutes approximately 90% of all cardiomyopathies. An estimated 30% of dilated cardiomyopathy cases have a genetic cause. Mutations in several genes have been linked to dilated cardiomyopathy, including genes encoding structural components of the sarcomere and desmosome. Nongenetic causes include inflammation of the myocardium due to an infection (mostly viral); exposure to drugs, toxins or allergens; and systemic endocrine or autoimmune diseases. Approximately 25% of all cases of dilated cardiomyopathy are of unknown etiology. Cardiac resynchronization therapy and implantable cardioverter-defibrillators may be required to prevent life-threatening arrhythmias.

Despite improved treatment, the mortality for dilated cardiomyopathy remains high, with a median period of survival of 1.7 years for men and 3.2 years for women. The annual incidence of sudden cardiac death is 2-4% and may be the initial presentation of dilated cardiomyopathy.
  The natural history of the condition is progressive, and its cost, disability, and morbidity are among the highest of any disease.

(See the dilated cardiomyopathy mages below.)

Chest radiograph shows a large heart. Image does n

Chest radiograph shows a large heart. Image does not provide any clue to the etiology of the dilated cardiomyopathy; however, the healing rib fractures and right lower lobe pneumonia (aspiration pneumonia) suggest alcoholic cardiomyopathy as the cause.

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Magnified right chest radiograph shows an area of

Magnified right chest radiograph shows an area of right lower lobe aspiration pneumonia in a patient with dilated cardiomyopathy (same patient as in the previous image).

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Imaging modalities

Currently available radiologic investigations are as varied in technique and sophistication as they are in cost. Studies vary from the noninvasive to the invasive and from the dynamic to the static. Radiologic tests are used to help make a diagnosis, to assess the degree of cardiac dysfunction, to identify a cause (though this is unusual), and to guide therapy.

It is difficult to make an accurate clinical identification of heart failure resulting from poor ventricular function, but it is important to do so because of the need to relieve symptoms. A substantial number of patients with heart failure have normal ECG results.
In other patients with apparent heart failure, echocardiography provides extra information on the nature of the cardiac disease that affects management.
In addition, providing appropriate treatment is important in patients affected more severely (ejection fraction < 35-40%), in whom treatment can significantly reduce mortality.

In a study by Merlo et al of 414 patients with dilated cardiomyopathy who underwent ECG testing, 55 patients experienced death or heart transplant and 57 patients experienced sudden death or malignant ventricular arrhythmias during a 125-month follow-up period. Left ventricular hypertrophy, heart rate, and anterolateral T-wave inversion predicted death or heart transplant. S wave amplitude in V2, R wave amplitude in DIII, and anterolateral T-wave inversion were predictors of sudden death or malignant ventricular arrhythmias.

The initial chest radiograph should usually be followed by echocardiography. These studies may be the only investigations required, and this approach is by far the most common method for diagnosing dilated cardiomyopathy. Subsequent evaluation of cardiac function may be performed by using cine computed tomography (CT) scanning (in rare cases), nuclear scintigraphy, or magnetic resonance imaging (MRI).

Although ultrafast CT scanners (electron beam) and multidetector-row CT scanners can be used with ECG gating to assess ventricular function, little reason exists to employ this equipment. CT scanners require ionizing radiation and injection of relatively large amounts of iodinated contrast agents.

Gated CT scanning is an accurate means of evaluating cardiac function, especially with the use of ultrafast CT scanning and 50-millisecond image acquisition. Only 1 short breath-hold period is required, and definition of the endocardial margins is excellent, allowing a degree of automation for defining the ventricular volumes. However, coverage of the entire heart may be difficult.

Cardiac MRI is excellent for assessing cardiac function in dilated cardiomyopathy because of the high intrinsic contrast between blood and myocardium, especially on cine MRA.
 Cine MRA is a repeatable examination, as compared with echocardiography, with less risk of intertest variation resulting from differences in operator or technique.
Cine MRA is especially suitable for evaluating the right ventricle, which is difficult to reliably image with other techniques.

MRI and MRA offer excellent noninvasive means of displaying cardiac and coronary anatomy.
They provide high spatial and contrast resolution, which can be used to evaluate congenital and acquired abnormalities and assess results of therapy.
 Pulse sequences (eg, cine MRA sequences) that provide high temporal resolution can be used to identify and quantify functional abnormalities.

Late gadolinium enhancement (LGE) cardiac MRI has shown strong prognostic value in many studies.

A retrospective study by Fu et al of 126 patients with idiopathic dilated cardiomyopathy (IDCM) with reduced left ventricular ejection fraction (LVEF< 40%) showed that the cardiac MRI parameters NT-proBNP (B-type natriuretic peptide), late‑gadolinium enhancement (LGE) mass, and LGE mass/left ventricle mass were significant predictors for major adverse cardiac events (MACEs).

Nuclear images can identify specific causes of left ventricular dysfunction, such as cardiac sarcoidosis and amyloidosis.

Limitations of techniques

Chest radiography is good for assessing the effects of cardiac dysfunction on pulmonary perfusion and the development of pulmonary edema, but radiographs seldom help in identifying the etiology of the dysfunction.

Echocardiography is an excellent method for assessing cardiac function, determining the presence of valve lesions, detecting complications such as thrombus or pericardial effusion, and assessing response to treatment. Echocardiography may be limited in 10-20% of patients by restricted acoustic access and is dependent on operator experience.

Cine CT scanning and CT angiography scanning require radiation and intravenous contrast enhancement; therefore, these techniques are seldom used.

Nuclear scintigraphy is a repeatable technique that often is used when serial examination of cardiac function is required. It is not as valuable as echocardiography, since it provides little anatomic information.

MRI and magnetic resonance angiography (MRA) are the most accurate methods for assessing cardiac anatomy or function. MRI/MRA is used when echocardiography is inadequate, but this study is often not used because of its relatively high cost and limited availability, as well as contraindications if ferromagnetic metallic foreign bodies are present in the patient.

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