Dilated Cardiomyopathies

Left Ventricular Dilation and Systolic Functional Impairment

The principal hallmark of DCM is left ventricular cavity dilation , although enlargement of other cardiac chambers also often occurs. Left ventricular cavity enlargement is usually quantified by measuring increased LV end-diastolic and end-systolic dimensions and volumes. Although the myocardial walls may be either of normal thickness or thinned, the total left ventricular mass is increased due to the overall increase in LV size. Furthermore, measures of LV systolic function such as fractional shortening, ejection fraction, stroke volume, and cardiac output are typically reduced ( Fig. 22.1 ).

It should be emphasized that, although the stroke volume is reduced in most cases, LV cavity dilation may initially serve to compensate by restoring stroke volume (measured on echocardiography as the difference between the LV end-diastolic and end-systolic volume). Namely, a larger ventricle can eject much more volume than a smaller one, even with the same amount of contraction (i.e., segmental deformation) ( Fig. 22.2 ). Hence, the final cardiac output may be initially preserved despite impairment in ejection fraction (measured as the stroke volume divided by LV end-diastolic volume). Restoration of stroke volume by ventricular dilatation is an integral part of the process of LV remodeling in the adaptation to changes in contractility and loading conditions. Thus, (1) in DCM, although inherent myocardial dysfunction and diminished myocardial contractility is the primary defect, ventricular dilation may enable the generation of the same amount of stroke volume with less deformation, and (2) in volume overload states (e.g., valvular regurgitation, such as functional mitral regurgitation), an increased amount of stroke volume is required and may be generated (with the same amount of contractility) by an LV that dilates to adapt (see Fig. 22.2 ). Indeed, preservation of stroke volume (as well as an increase in heart rate) to maintain overall cardiac output may explain why the severity of symptoms can remain relatively low despite notably impaired left ventricular ejection fraction (LVEF), despite the fact that the latter correlates strongly with prognosis. Conversely, symptoms of congestive heart failure are more directly related to elevated LV filling pressures (see below). Fig. 22.1 and Video 22.1 provide an example of two patients with severely dilated left ventricles and severely reduced LVEF but different LV stroke volumes, atrial sizes, and functional class.

Based on the described principles of remodeling, the left ventricular shape changes with disease progression from the typical elongated shape to a more globular one. A simple measurement that can quantify this is the sphericity index , defined as the ratio of the LV length and width ( Fig. 22.3 ). A normal sphericity index is greater than 1.6; in DCM, this is generally reduced , implying pathologic remodeling with notable cavity dilation (see also Fig. 20.5 in Chapter 20 ).

Several features of DCM are manifest and quantifiable on m-mode echocardiography (see Chapter 2 ): LV and right ventricular (RV) cavity enlargement, changes in wall thickness and calculated LV mass, as well as reduced segmental wall thickening are classically recognizable on m-mode as signs of LV dilation and poor systolic performance. Poor aortic valve opening with premature closure can be noted in the setting of reduced stroke volume. Due to LV dilatation, the mitral leaflet echoes are often distanced to greater than 1.0 cm of the mitral E-point from the interventricular septum (see Fig. 2.16 ). A characteristic pattern of decreased mitral leaflet opening and an occasional “b-notch” indicative of markedly elevated LV end-diastolic pressure are shown in Fig. 2.15 in Chapter 2 . Impairment in LV systolic function can also be assessed on apical windows by reduced mitral annular planar systolic excursion (MAPSE) ( Fig. 22.4 ). A MAPSE less than 10 mm (usually averaged from 2 to 4 point measurements spaced around the mitral annulus) is indicative of reduced longitudinal LV motion.

Similarly to reduced MAPSE, impaired motion of the base of the heart towards the more stationary apex (expressing the longitudinal function of the LV) can be quantified by Doppler Tissue Imaging S’ (systolic) velocity or more advanced parameters of myocardial deformation, such as systolic strain, which is often expressed as global longitudinal strain ( Fig. 22.5 ) or less frequently as systolic strain-rate (see Chapter 6 ), all of which will typically be reduced in DCM.

Finally, Doppler echocardiography may be used in the hemodynamic assessment of LV systolic function: in addition to volumetric measurements of stroke volume and cardiac output, these calculations can also be performed using the continuity of flow equation (see Chapter 1 ). Multiplication of the cross-sectional area and the time velocity integral of the left ventricular outflow tract (LVOT) will provide the calculation of left ventricular stroke volume ( Fig. 22.6 ), which is typically reduced in advanced DCM. The change of pressure over time (d P /d t ) can be measured when a sufficient mitral regurgitation envelope (recorded by continuous wave Doppler) is present and will also be reduced in most patients with DCM ( Fig. 22.7 ). This noninvasive parameter has shown good correlation with values measured by cardiac catheterization and has been associated with worse prognosis when less than 600 mm Hg/s. For more details on the assessment of LV systolic function, please refer to Chapter 14 .

Dilated cardiomyopathies that develop due to processes affecting the heart more globally, such as genetic DCM, postmyocarditis, postpartum, and toxic/metabolic etiologies, mostly present with diffuse LV hypokinesis . However, diseases such as sarcoidosis, stress cardiomyopathy, ACM, and some postmyocarditis states may affect the heart in a more regional pattern, with a predilection for certain hypokinetic or akinetic areas (see Chapter 41 ). Wall motion abnormalities that do not follow any specific coronary artery territory are often the clue that a true (nonischemic) cardiomyopathy exists. Also, the basal segments of the ventricular walls are often the last segments to remain normokinetic in DCM.

The severe impairment in contractility leading to akinetic or dyskinetic areas and cavity dilation creates a nidus for the formation of intracardiac thrombi , which are predominantly mural and most frequently occurring in the apex of the LV ( Fig. 20.2 , Fig. 38.8 and corresponding Video 38.4 , and Fig. 38.9 ). Spontaneous echo contrast may also be seen, mainly within the cavity of the LV.

Elevation of Left Ventricular Filling Pressures

Although the severity of LV dysfunction expressed by LVEF relates to prognosis, its correlation with symptom severity is poor. Symptoms of congestive heart failure in patients with DCM relate better to the filling pressures of the left ventricle, which can be well assessed noninvasively by Doppler echocardiography (see Chapter 21 ). Some degree of diastolic dysfunction nearly always accompanies the reduced systolic function in DCM. However, the severity of impairment of diastolic dysfunction does not necessarily correlate to the impairment of systolic function (and vice versa). With regard to symptoms, patients with an impaired relaxation pattern seen in the Doppler trace of mitral inflow will often tend to have dyspnea falling within the lower New York Heart Association functional classes, whereas higher grades of dyspnea are often associated with pseudonormal filling or even more frequently with restrictive filling patterns ( Fig. 22.8 ). One of the main features of restrictive filling is a very short deceleration time of the E wave, which has also been proven as a reliable harbinger of poor prognosis in DCM patients. Of note, higher grades of diastolic dysfunction will most often be accompanied by predominantly diastolic flow in the pulmonary venous waveforms, which is also indicative of markedly increased left atrial (LA)/LV filling pressures. Initiation of diuretic and vasodilator therapy may reduce LV filling pressures and thus improve the pattern of transmitral flow as well as the functional class of the patient.

Left Atrial Dilation

An increase in LV filling pressures, discernable from the mitral inflow pattern, will over time lead to left atrial dilation , which can be quantified by an enlargement in LA diameter on 2D or M-mode echocardiography, or more precisely an enlargement in LA area and/or volume, measured by tracing the LA cavity in one or preferably two imaging planes (see Fig. 22.1 ). For clinical purposes, it is best to index the measured LA area and volumes to the body surface area of the patient. In some patients, LA enlargement is also accompanied by an impairment in LA function, which can easily be noticed on the mitral inflow pattern as a minimal or absent A wave. The frequent occurrence of atrial fibrillation in markedly enlarged atria denotes the intricate relation between abnormal atrial morphology and function.

Right Heart Dilation and Functional Impairment

Right heart chambers may also exhibit dilation and/or functional impairment in the setting of DCM. Primarily, this may be caused by the disease affecting the myocardium of both ventricles. Furthermore, a sustained increase in LV filling pressures may over time lead to pulmonary hypertension, which may in turn induce right ventricular overload, dilation, and functional impairment. The assessment of RV size is predominantly based on the measurement of its end-diastolic diameters (either in the parasternal long-axis view, or most frequently by measuring the widest diameter of the RV cavity in the apical four-chamber view, as in Fig. 16.4 ). Furthermore, RV area and volumes can also be measured, but due to the complex crescent-shaped geometry of the RV, these measurements are often unreliable when obtained with 2D echocardiography. Several measures of RV function may be seen to decline when the RV becomes myopathic: a decrease in fractional area change (FAC) to ≤35%, or reduced tricuspid annular planar systolic excursion (TAPSE) to ≤16 mm and/or a reduced Doppler tissue imaging (DTI) S′ of the tricuspid annulus to ≤10 cm/s, reflecting impaired shortening of the RV myocardium in the longitudinal directions, may all be detected in patients with DCM affecting the right heart ( Fig. 22.9 ).

Pulmonary artery pressures can be assessed noninvasively by measuring the peak velocity, that is, peak gradient of the tricuspid regurgitation jet by Doppler echocardiography, applying the simplified Bernoulli equation (see Chapter 1 ), and adding in estimated right atrial pressure to sum up the total RV systolic pressure.

Impaired RV function and elevated pulmonary artery pressures are well-known determinants of poor outcomes in patients with heart failure, including those with DCM. Thus, the evaluation of right heart morphology and function, as well as the assessment of pulmonary artery pressures should not be neglected in patients with DCM. If implantation of a ventricular assist device (VAD) is being considered, a comprehensive assessment of right heart function is important for anticipation of potential severe right heart failure postoperatively (see Chapter 26 ). Further details on the assessment of RV structure and function as well as pulmonary hypertension are covered in Chapter 16, Chapter 36 , respectively.

Functional Mitral Regurgitation

Within the context of pathological LV remodeling in DCM, an increase in LV spherical remodeling occurs, resulting in lateral and apical displacement of the papillary muscles. In addition to mitral ring dilation that parallels LV cavity dilation, papillary muscle displacement leads to poor mitral leaflet coaptation and is the main mechanism underlying secondary (functional) mitral regurgitation (see Fig. 28.10 ). Progression of mitral regurgitation is yet another harbinger of worse prognosis in DCM patients. Finally, severe mitral regurgitation causes marked volume overload and further dilation of the LV, which may in turn increase the calculated LVEF, thus concealing the actual underlying grave impairment in LV systolic function.