In its simplest form, cardiomyopathy (CMP) can be defined as a cardiac disorder involving myocardial dysfunction. Though there are various formal definitions of CMP in the literature, the two major ones are from the World Health Organization (WHO) and from the American Heart Association (AHA). The WHO definition is more clinical, while the AHA definition is more molecular and scientific in its delineation. For the purpose of this chapter, we follow the simpler definition by WHO as it lends itself well to the echocardiographic evaluation of cardiomyopathies.
Cardiomyopathies can also be defined by their etiology, as was done also by the WHO task force in 1995. Since the etiology may not always be obvious, such as in many cases of dilated CMP, this classification is also less useful when discussing the general principles of echocardiographic diagnosis of CMP. The various types of cardiomyopathies, as classified by WHO, are listed in Table 14-1. Each type of CMP can have various etiologies, the discussion of which is beyond the scope of this chapter (see suggested reading list for further information). The various etiologies are nonetheless listed in Table 14-2. Table 14-3 demonstrates the key elements in the echocardiographic evaluation of a patient with a CMP.
|Type of CMP
|Idiopathic (mostly genetic)
|End-stage valvular heart disease
|End-stage hypertensive heart disease
|Infectious (viral myocarditis, Chagas, bacterial, etc.)
|Toxic/metabolic (chemotherapy, alcoholic, cocaine, etc.)
|Rheumatologic (SLE, scleroderma)
|Endocrine disorders (diabetes, thyroid disease, etc.)
|Neuromuscular diseases (Duchenne’s, myotonic dystrophy, etc.)
|Electrolyte abnormalities (hypocalcemia, hypophosphatemia, etc.)
|Nutritional deficiencies (thiamine, carnitine, etc.)
|Infiltrative diseases (usually end-stage)
|Infiltrative (amyloidosis, sarcoidosis, etc.)
|Storage diseases (hemochromatosis, glycogen storage diseases, etc.)
|Isolated LV noncompaction
|LV apical ballooning syndrome
|Assessment of chamber sizes and mass
|Left ventricular and left atrial dilatation
|Right ventricular dilatation, either primarily or from pulmonary hypertension
|Increased cardiac mass and hypertrophy
|Assessment of valvular function and valve apparatus
|Tricuspid regurgitation, usually secondary from pulmonary hypertension
|Mitral valve regurgitation, either due to primary dysfunction of the valvular apparatus or secondary to annular dilatation
|A change in the position of the papillary muscles
|Assessment of systolic and diastolic function
|Doppler flow patterns across the mitral valve
|Tissue Doppler interrogation
|Wall motion abnormalities, either segmental or global
|Grading the systolic and diastolic dysfunction
|Assessment of right heart pressures, as this will influence treatment and prognosis
|Assessment of other features
|Left atrial or left ventricular thrombus
|Appearance of the endocardium
|Assist in the diagnosis of amyloidosis or LV noncompaction, for example
As we describe the echocardiographic features of the various cardiomyopathies, we will incorporate the elements described above. The reader should recognize that this chapter assumes familiarity with the basic echocardiographic views and how to obtain those views. It also needs to be emphasized that the two-dimensional image and M-mode interrogations need to be of good quality to make reliable interpretations.
Dilated cardiomyopathies have various etiologies, and the dilated state usually represents the response of the myocardium to the various insults. Though the dilated state may represent a common response to multiple types of insults, every effort should be made to identify a potentially remediable cause, as this may significantly influence the prognosis. Dilated cardiomyopathies generally are classified as either ischemic or nonischemic, the latter category being rather broad and inclusive of those caused by valvular diseases (Table 14-2).
Echocardiography is a critical tool in assessing patients with a dilated CMP, and, in some cases, can help elucidate the etiology of the CMP and gauge prognosis and response to treatment. The most common clinical presentation of a patient with a dilated CMP is congestive heart failure, associated with dyspnea and a fluid overload state. Echocardiographic evaluation of a patient presenting with dyspnea, with or without a fluid overload state, should be undertaken early in the course of management if a clear etiology is not evident on presentation, such as symptoms or signs of coronary ischemia, electrocardiograpahic changes suggestive of myocardial ischemia, a history of known CMP, or a recent echocardiogram. If a remediable etiology is suspected, like coronary ischemia and mitral regurgitation (MR), every effort should be made to alleviate the condition. Echocardiography should still be carried out in such a case, and the timing should depend on the availability of the ultrasound equipment and the delay it might cause in treatment. However, the current availability of good-quality portable equipment can expedite such evaluations.
The echocardiographic diagnosis of a dilated CMP rests solely on the demonstration of a dilated, hypofunctional left ventricle. Though various secondary features are frequently evident on the ECG, the diagnosis can only be made by the demonstration of left ventricular (LV) dilatation.
LV dilatation is best evaluated in the parasternal long-axis view (Figure 14-1A), (Videos 14-1 and 14-2). The spherical change in the LV cavity with dilatation is more apparent in this view and is represented by an increasing vertical axis when compared with the horizontal axis (Figure 14-1B). Global dilatation of all four chambers, however, is better appreciated in the apical four-chamber view. The LV dilatation may be mild, moderate, or severe, and accurate measurements are important to grade the degree of dilatation. The short-axis view at the level of the papillary muscles is also a good view to assess LV dilatation. If there is difficulty in visualizing the endocardium, echocardiographic contrast can be used; the risk/benefit ratio of the use of such agents should be assessed in each individual patient (we recommend avoiding the agents in acute ischemia and in acute heart failure).
(A) A two-dimensional image of a parasternal long-axis view in a patient with a dilated cardiomyopathy. Note the dilated LV and the increased long axis of the LV. (B) Two-dimensional image of an apical four-chamber view of a patient with a dilated cardiomyopathy. Note the spherical change in the LV cavity with the dilatation. *Aortic root and aortic valve. LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.
LV wall motion is universally impaired in patients with a dilated CMP (Figure 14-2A,B). The wall motion abnormalities may well be regional in patients with an ischemic etiology (Figure 14-2A–C). These regional abnormalities correlate well with impairment of vascular supply to the dysfunctional wall. However, basal wall motion may be better preserved than other regions in some patients with a nonischemic, dilated CMP, leading to occasional confusion with ischemic CMP. This should be kept in mind when trying to distinguish between ischemic and nonischemic etiologies. Another potential issue may arise in patients with a dilated CMP and a left bundle branch block or a dilated CMP and previous cardiac surgery. The bundle branch abnormality may be from the increased mass from the cardiac dilatation or from an ischemic injury in the left anterior descending coronary artery territory. A dyssynchronous septum is seen in such patients and is evident in the parasternal long-axis and the apical four-chamber views. In such cases, one should concentrate on looking at other walls to make the distinction between regional and diffuse wall motion abnormalities. In patients with a previous anterior wall myocardial infarction, other wall motion abnormalities will be apparent, such as apical and/or anterior lateral hypokinesis, akinesis, or dyskinesis. Furthermore, infarcted tissue will appear thinned on two-dimensional imaging (Figure 14-2C).
(A) M-mode through the mitral valve in a normally contractile heart. Note the close relationship of the mitral E wave (single arrowhead) with the septal M-mode (double arrowheads). This is called the EPSS (E-point septal separation). (B) M-mode recording through the mitral valve in a patient with a dilated cardiomyopathy. Note the significantly abnormal separation between the mitral valve E wave (single arrowhead) and the septal M-mode (double arrowheads). The EPSS is abnormal in this patient. Also note the lack of motion and thickening with systole in the M-mode of the septum and the posterior wall (triple arrowheads). Systole is marked by the vertical solid white line. (C) Two-dimensional imaging in the parasternal long axis in a patient with a previous myocardial infarction. Note the thinned-out septum that is akinetic (arrowhead). The septum bows into the right ventricle with systole. (D) M-mode imaging in the parasternal long-axis view through the aortic root and aortic valve. Note the relatively “flat” motion of the aortic root during the cardiac cycle (single arrowhead) and the “trapezoidal” pattern of aortic valve motion (double arrowheads). See the text for more information.
Though two-dimensional imaging is excellent at assessing wall motion, the importance of M-mode interrogation is often overlooked. M-mode interrogation may allow a better assessment of wall motion than two-dimensional imaging in circumstances where the endocardium is not well visualized by the two-dimensional approach. M-mode imaging is also important in gauging wall thickness. During normal contractility of a myocardial segment, there is motion inward toward the ventricular cavity and associated thickening. M-mode imaging can exhibit the presence or absence of both these phenomena quite well.
Various other features (also called secondary features) may also be evident in patients with a dilated CMP.
A common secondary feature is MR (also called functional MR) (Figure 14-3). This occurs due to a relative dilatation of the mitral annulus. As the left ventricle dilates and approaches a spherical shape, the mitral valve apparatus is pulled apically. This results in a relative dilatation of the mitral annulus, leading to MR. One has to make an effort, clinically, to sort out whether the MR is a primary phenomenon resulting in the dilated CMP or whether it is the result of the dilated CMP. A transesophageal echocardiogram (TEE) may help in resolving the issue. If the mitral valve apparatus appears structurally normal (absence of leaflet or chordal redundancy, absence of valve thickening, absence of annular calcification, absence of papillary muscle dysfunction), and an ischemic cause of the regurgitation is ruled out, then one should consider the etiology of the regurgitation to be related to the dilated CMP. The best determination of an etiology is important as it may influence the treatment approach and the choice of surgical repair technique for a particular patient. Furthermore, etiology, along with hemodynamic status and LV mechanical status, also influences prognosis with or without surgical treatment. When present secondary to a CMP, the regurgitant jet is usually central (the cause is relative annular dilatation) (Figure 14-3). Various criteria have been established to judge the severity of the regurgitant jet, and though some are better accepted than others, demonstration of flow reversal in the pulmonary veins during systole and a high peak inflow velocity across the mitral valve are good correlates of severe regurgitation. A standard TEE or a three-dimensional study may be superior to standard two-dimensional imaging for determining the severity of the regurgitation. TEE particularly, also helps in deciding the appropriate surgical approach (valve repair/reconstruction vs. replacement).
In addition to the M-mode features described above, there are other features that should be reviewed when performing an echocardiographic examination of a patient with a dilated CMP.
This is best assessed in the parasternal long-axis view with the ultrasound beam through the mitral leaflets (Figure 14-2A,B). The E point of the mitral valve opening is quite close to the septal wall on M-mode imaging in normal individuals. However, this distance is significantly increased in patients with a dilated CMP (Video 14-1).
In normal circumstances, there is a sinusoidal pattern of motion exhibited by the aortic root with anterior motion during systole (Figure 14-2D). This is best seen in the parasternal long axis, with the ultrasound beam focused through the aortic root at the level of the aortic leaflets. In patients with a dilated CMP, the normal sinusoidal pattern is replaced by a relatively flat pattern of motion.
The normal pattern of aortic valve opening and closing appears as a rectangular box on M-mode imaging performed in the parasternal long-axis view through the aortic valve (Figure 14-2D). In cases of reduced stroke volume (SV), as is the case in dilated CMP, there is poor opening of the aortic valve and the valve tends to start closing earlier in systole. The pattern changes from that of a rectangular box to a more “trapezoidal” box.
The presence of a mural thrombus in the LV cavity on two-dimensional imaging can be seen in a dilated CMP (Figure 14-4). In cases of ischemic CMP, the thrombus is most often seen in an akinetic and/or aneurysmal segment. The presence of thrombus must be distinguished from the endocardium. Though this is usually straightforward, there are helpful techniques that can be utilized if confusion exists. Contrast enhancement can be used to delineate the endocardium. Usually, the contrast will outline the thrombus by circumventing it. Color-flow can also be used in a similar fashion. A color sector focused on the area of concern will outline the thrombus, as color will not go into thrombus. Care should be taken to not have too much gain on the color jet, as this may well obscure the delineation between the thrombus and the endocardium.
(A) Two-dimensional imaging in the apical four-chamber view demonstrating a left ventricular thrombus in the apex (arrowhead). (B) Apical four-chamber view demonstrating a left ventricular thrombus in the apex (single arrowhead). The thrombus occupies most of the apex. Incidentally, also note the pericardial fluid around the right atrium (double arrowheads). LA, left atrium; RA, right atrium; RV, right ventricle.
Left atrial dilatation is a universally associated finding in dilated CMP. Left atrial size and volume correlate well with the severity and duration of the dilated CMP. The left atrial dilatation is caused by multiple reasons, including the secondary MR, increased diastolic pressures, and potential involvement of the left atrium itself by the myopathic process. Spontaneous echo contrast can be seen commonly in the left atrium because of impaired of blood flow, and may be more prominent if there is associated atrial fibrillation.
There are various right heart-related findings that can be seen in patients with a dilated CMP (Figure 14-5). These include tricuspid regurgitation, right ventricular (RV) dilatation, and pulmonary hypertension. The RV dilatation is either secondary to pulmonary hypertension, which is commonly seen in such patients, or due to involvement by the myopathic process. The tricuspid regurgitation, in most cases, is a secondary phenomenon from the pulmonary hypertension and RV dilatation, the latter resulting in tricuspid annular dilatation.
(A) Apical four-chamber view with color-flow showing tricuspid regurgitation. (B) Continuous-wave Doppler recording through the tricuspid valve during systole. There is tricuspid regurgitation present, and the peak gradient across the right ventricle and the right atrium is 46.4 mmHg. If one assumes a right atrial pressure of 10 mmHg and the absence of pulmonic valve stenosis, then the estimated pulmonary artery pressure is 56.4 mmHg, consistent with moderate pulmonary hypertension.
Assessment of systolic and diastolic performance should be done in all patients with a CMP, regardless of type. The relative impairment in these indices is predictive of prognosis and clinical course. Though the evaluation of systolic and diastolic function is described in this section with reference to dilated CMP, similar principles apply with other types of cardiomyopathies.
Doppler interrogation of all patients with a dilated CMP is important, as it can assist with the assessment of systolic and diastolic function, which helps predict prognosis. The most important predictors of survival in dilated CMP are end-diastolic and systolic volumes and ejection fraction.
The principles of laminar flow are used in determining the various indices of systolic function. This includes an assessment of SV and cardiac output (CO). The pulsed Doppler can be used to interrogate the flow in the left ventricular outflow tract (LVOT) over a period of time. This generates the time–velocity integral (TVI) (sometimes also referred to as velocity–time integral [VTI]). The mechanical status of the left ventricle is a key component in determining the TVI. Assuming the principles of laminar flow, the SV is a product of the LVOT cross-sectional area (CSA) and the TVI (SV = TVI × LVOT CSA). CO, in turn, is defined as the product of the SV and the heart rate (HR). Because the LVOT CSA can be assumed to be stable for a given patient, and hence a constant, the change in TVI is directly proportional to the change in the LV mechanical status. Hence, an increase in the LVOT TVI can be used as gauge for improvement in LV systolic function when a therapy is undertaken, such as initiation of inotropic support, alleviation of coronary ischemia, treatment of valvular insufficiency with afterload reduction, placement of an intra-aortic balloon pump, or a combination thereof. With appropriate therapy, not only is there an increase in the TVI, but the shape of the envelope also changes from a more parabolic and somewhat blunted one to a more triangular one. Measurements of the acceleration and deceleration times of the mitral regurgitant jet have been identified as predictive of prognosis. These times correlate well with dP/dt (a measurement of LV contractility) obtained at cardiac catheterization in similar patients. An acceleration time (dP/dt) of <600 mmHg/s and a deceleration time (DT) (−dP/dt) of <450 mmHg/s identifies a significantly higher risk group, with a decreased event-free survival.
Doppler assessment of diastolic function relies on interrogation techniques and evaluation of a few key parameters: mitral valve inflow patterns, tissue Doppler interrogation (TDI) techniques, the isovolumic relaxation time (IVRT), mitral flow deceleration time, and pulmonary vein flow patterns (Figure 14-6). It is important to utilize a combination of the above findings to arrive at a decision regarding the diastolic function of a patient. These parameters tend to be the most predictive with the presence of systolic dysfunction and can be altered by various other clinical issues, such as valvular disease, HRs, and therapeutics. Though a detailed discussion of these parameters is beyond the scope of this chapter, basic principles of the use of Doppler in evaluating diastolic dysfunction are discussed.