This entity is characterized by dilation and diminished contraction of the left or both ventricles. End-systolic and end-diastolic volumes are increased, whereas stroke volume and ejection fraction are decreased. Mild to moderate mitral regurgitation and tricuspid regurgitation are frequently associated with the ventricular enlargement. The wall thickness of the left ventricle is usually within the normal range, so that an overall increases in LV mass results. There are many causes of dilated cardiomyopathy (Table 33-2). However, most cases have no identifiable cause (idiopathic). The most common cause of dilated cardiomyopathy is myocardial ischemia secondary to coronary artery disease in which the degree of myocardial dysfunction is frequently not explained by the obvious extent of myocardial infraction. Hypertension, viral diseases, alcoholism, diabetes, obesity, several toxins, and hereditary factors also lead to dilated cardiomyopathy. The most common clinical feature of dilated cardiomyopathy is LV failure. Mural thrombus may form in the dilated left ventricle.

A variety of distribution patterns of inappropriate myocardial hypertrophy develop in the absence of an obvious hemodynamic stress (increased afterload), such as aortic stenosis or systemic hypertension (Table 33-3). The disease is genetically transmitted in about half of the cases and follows an autosomal dominant inheritance pattern with variable penetrance. Possible manifestations are symmetric involvement of the entire left ventricle or both ventricles or asymmetric hypertrophy of the upper septum, midportion of the ventricular septum, or apex. Nonobstructive and obstructive hypertrophic cardiomyopathy can be distinguished by the associated hemodynamic alterations. Asymmetric septal hypertrophic cardiomyopathy can cause obstruction of the LV outflow tract. The hallmark is dynamic subvalvular aortic stenosis. During diastole, the LV outflow tract appears normal or slightly narrowed because of the presence of upper septal hypertrophy. Increasing stenosis develops during systole as the anterior leaflet of the mitral valve moves in an anterior direction toward the septum, thereby narrowing the outflow tract. Although uncommon in the Western world, apical hypertrophy is prevalent in Japan. This type of hypertrophic cardiomyopathy does not cause obstruction of the outflow tract. Midventricular type involves hypertrophy of the middle of the LV with mid cavity obliteration in systolic causing high wall tension in the isolated LV apex. LV apical dyskinesis or aneurysm is frequent. Symmetric hypertrophic cardiomyopathy is also recognized and may be a particularly severe form. Involvement of the right ventricle is a feature of the disease in infants and children.

This entity is characterized by hampered ventricular filling secondary to myocardial diastolic stiffness. Flow into the ventricles is rapid during early diastole; it then plateaus, and little filling takes place in late diastole. End-diastolic pressure is elevated in both ventricles, whereas systolic function is normal or only slightly reduced. Endomyocardial fibrosis and Loeffler endocarditis are now classified as types of restrictive cardiomyopathy. Loeffler endocarditis is associated with hypereosinophilia. Degranulation of endomyocardial eosinophils is suspected to be responsible for focal necrosis and subsequent fibrosis and for the formation of mural thrombus. Increased stiffness of the ventricular walls and reduction of the cavity by organized thrombus contribute to the restrictive filling pattern. Endomyocardial fibrosis, a different entity with a peak geographic distribution in equatorial Africa, is not associated with hypereosinophilia. In this disease, fibrosis of the apex and subvalvular regions leads to restrictive cardiomyopathy. Glycogen storage diseases, radiation fibrosis, and certain infiltrative diseases, such as amyloidosis and sarcoidosis, can also cause restrictive cardiomyopathy. Many cases of restrictive cardiomyopathy are idiopathic.

Specific cardiomyopathies are myocardial diseases that are associated with a specific cardiac or systemic disease. Hemochromatosis, sarcoidosis, amyloidosis, and hypertensive or metabolic cardiomyopathy are examples of specific cardiomyopathies. Dilated cardiomyopathy may be the result of inflammation (myocarditis).

Several classifications also consider infiltrative cardiomyopathy as an additional category (Table 33-4). The definition of infiltrative cardiomyopathy refers solely to the histopathologic mechanism of infiltration of myocardial tissue, and the diseases in this group may cause either restrictive or dilated cardiomyopathy. Hemochromatosis is an example of an infiltrative cardiomyopathy in which the cardiomyopathy is of the dilated type, whereas amyloidosis usually causes a restrictive pattern.

The morphologic characteristics of dilated cardiomyopathy are clearly depicted on ECG-gated SE MRI or cine MRI (Figs. 33-7 and 33-8) (Table 33.5). Morphologic changes include enlargement of the left ventricle and sometimes the right ventricle and atria. The thickness of the LV wall usually remains normal. The MRI features in dilated cardiomyopathy are frequently nonspecific, so that the
various underlying causes cannot be distinguished. However, it is usually possible to distinguish between ischemic and nonischemic forms of dilated cardiomyopathy. In most cases of nonischemic dilated cardiomyopathy, the wall thickness of the left ventricle is uniform; no regional wall thinning is recognized. If the cardiac dilation is caused by prior myocardial infarction and ischemia, usually one or more regional areas of severe wall thinning with or without ventricular aneurysm are seen. MRI may demonstrate localized ventricular dilation after occlusion of a major coronary artery rather than global dilation; the latter is characteristic of dilated cardiomyopathy. Delayed contrast-enhanced MRI may be used to demonstrate regional hyperenhancement in a subendocardial or transmural distribution at the site of prior myocardial infarction to distinguish patients with ischemic cardiomyopathy (Fig. 33-9). Regional delayed hyperenhancement is not a usual feature of idiopathic dilated cardiomyopathy (Fig. 33-9). A minority of patients (almost 30%) with idiopathic dilated cardiomyopathy show delayed contrast enhancement. The hyperenhancement is not subendocardial but rather in a midwall distribution especially in the septum. These may be cases of myocarditis presenting in the chronic phase as dilated cardiomyopathy.

Ventricular mass, ventricular thickness, and ventricular volumes can be quantified with cine MRI to determine the severity of dilated cardiomyopathy. Cine MRI measurements of LV volumes, mass, and ejection fraction in dilated cardiomyopathy have been shown to be highly reproducible between studies. The 3D data set with MRI is especially useful for monitoring LV dimension and function over time. Because of its high degree of accuracy and reproducibility, MRI can be used to monitor the effect of treatment in individual patients and in clinical studies to assess the efficacy of new therapeutic interventions. For example, significant decreases in LV systolic volume, wall stress, and mass and increase in ejection fraction have been shown in dilated cardiomyopathy after angiotensin-converting enzyme inhibitor treatment and other therapies.

Although the right ventricle is usually less dilated and its systolic function is less severely depressed, RV diastolic abnormalities, such as an increased time to peak filling rate, have been detected using cine MRI and VEC (phase contrast) cine MRI. The profile of diastolic inflow velocity measured in the region of the tricuspid valve is flattened in comparison with that in healthy volunteers. It is suspected
that the altered morphology and function of the left ventricle causes functional changes in RV filling.

The signal intensity on SE and GRE images has not been found to be consistently altered in dilated cardiomyopathy, except in cardiomyopathy associated with hemochromatosis (Fig. 33-10). Shortening of relaxation rates has been shown on SE, T2^*, and GRE images of myocardium overloaded with iron.

Mural LV thrombus can be readily identified on cine MR images and on DE-MR (delayed gadolinium-enhanced inversion recovery GRE) images. The most frequent site of thrombus is the LV apex (Fig. 33-11).

The initial diagnosis of hypertrophic cardiomyopathy is nearly always established by echocardiography (Table 33.6). The typical diagnostic feature on any imaging modality is a ratio of the end-diastolic thickness of the septum to the posterolateral wall greater than 1.5. Because not all patients have asymmetric hypertrophy, an additional criterion is concentric hypertrophy (end-diastolic wall thickness greater than 1.2 cm) in the absence of a cause for hypertrophy, such as hypertension, aortic stenosis, or extreme isometric exercise. MRI enables a precise delineation of the location and extent of hypertrophic myocardium in persons with hypertrophic cardiomyopathy (see Figs. 33-1,33-2 and 33-3, 33-5, and 33-12,33-13,33-14,33-15 and 33-16). One of the major clinical roles of MRI is to evaluate unusual forms of hypertrophy that are difficult to assess with echocardiography (Figs. 33-17 and 33-18). Another indication for MRI is sequential monitoring of the LV mass and assessment of prognosis using delayed MRI, the extent of delayed enhancement is related to morbidity and mortality.