Myocardial Pathology

Published on 21/06/2015 by admin

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13 Myocardial Pathology

David S. Owens, Mariska Kemna

Hypertrophic Cardiomyopathy

Background

• Hypertrophic cardiomyopathy (HCM) is characterized by pathologic thickening of the left ventricle (LV) due to sarcomeric gene mutations.

• HCM commonly involves asymmetrical hypertrophy of the anterior septum, but can manifest as concentric hypertrophy or hypertrophy of other segments (Figs. 13-1 through 13-3).

• Resting left ventricular outflow tract obstruction (LVOTO) due to systolic anterior motion of the mitral apparatus is present in about one third of HCM patients; another one third has provocable obstruction.

• The presence of LVOTO is neither necessary nor sufficient to diagnose HCM.

• A diagnosis of HCM is suggested by wall thickness greater than 1.5 cm in adults or a Z score indexed to body surface area of more than 2 in children (in the absence of other causes for hypertrophy).

• Structural or valvular abnormalities that increase left ventricular afterload (e.g., aortic stenosis, coarctation of the aorta) need to be excluded before a diagnosis of HCM can be made.

• Other conditions that mimic HCM include hypertensive heart disease, infiltrative disorders (e.g., amyloidosis), and glycogen storage disorders (e.g., Fabry disease, Danon disease, PRKAG2 mutations).

• In infants, 30% to 50% of cases of an HCM-like phenotype can be attributed to metabolic or syndromal disorders (e.g., Noonan syndrome). Infants born to diabetic mothers can have transient biventricular hypertrophy.

• Physiologic adaptation to exercise can lead to mild to moderate ventricular hypertrophy, which can mimic HCM. Features distinguishing “athlete’s heart” from HCM are shown in Table 13-1.

• Massive left ventricular hypertrophy (LVH)—wall thickness greater than 30 mm in adults or a Z score for body surface area greater than +15 in children—is a risk factor for sudden death in HCM patients.

Figure 13-1 Parasternal long axis and short axis two-dimensional images of a patient with classic reverse curvature hypertrophic cardiomyopathy (HCM) and primary involvement of the basal anterior septum. Measurement of maximal wall thickness is performed at the greatest diameter, excluding right ventricular band insertion.

Figure 13-2 Apical four-chamber (4C) view of a patient with mid-ventricular HCM demonstrating mid-ventricular and papillary muscle hypertrophy and secondary apical aneurysm formation due to midventricular obstruction.

Figure 13-3 Apical 4C echocardiographic (left) and cardiac magnetic resonance imaging (MRI) (right) views of a patient with apical HCM. Cardiac MRI can provide a good depiction of apical thickness and function when echocardiographic imaging is inadequate.

TABLE 13-1 FEATURES DISTINGUISHING “ATHLETE’S HEART” FROM HCM IN ADULTS *

Feature	Athlete’s Heart	HCM
Maximal wall thickness	≤16 mm	≥13 mm
Pattern of LVH	Predominantly concentric	Concentric or asymmetrical
LV cavity dimension	Often > 55 mm (in endurance athletes)	Usually < 45 mm
Diastolic function	Normal	Normal or abnormal
Gender	Male > female	Male = female
Family history of HCM or SCD	No	Yes or no
Delayed enhancement (MRI)	No	Yes or no
Exercise capacity	Above normal	Normal to below normal
Response to deconditioning	LVH regression	No change in LVH

* Intended for adults or adult-sized teenagers. Corresponding Z scores can be calculated for children but have not been validated.

Echocardiographic Approach (Table 13-2)

Anatomic Imaging

• Step 1: Assess the magnitude and extent of LVH.

• Whenever possible, wall thickness measurements should be confirmed in more than one imaging plane (see Fig. 13-1).

• Short axis view imaging of the LV at multiple levels usually provides the best means of assessing wall thickness and overall hypertrophy.

• The right ventricular moderator band and papillary muscle insertions should not be included in wall thickness measurements. The parasternal long axis view is most susceptible to mismeasurement.

• Apical windows may be more suited to estimating LV wall thickness of the inferior septum and lateral wall, common regions of dropout on short axis view imaging.

• Use of contrast agents can improve endocardial border detection in patients with suspected midcavitary or apical hypertrophy.

• Step 2: Quantify systolic function.

• HCM patients often have an increase in circumferential shortening, but a decrease in longitudinal shortening.

• Hyperdynamic systolic function is also commonly seen in hypertensive heart disease or situations of decreased afterload.

• A small subset (∼5%) of HCM patients have declining LV systolic function due to progressive fibrosis.

• Step 3: Assess mitral leaflet motion for possible systolic anterior motion (SAM).

• SAM is best viewed in either the parasternal or apical long axis windows (Fig. 13-4).

• M-mode depiction of mitral leaflet motion is essential for determining the timing of SAM and the duration of mitral-septal contract (Fig. 13-5).

• The presence of LVOTO in the absence of SAM suggests fixed subaortic stenosis, and additional causes of obstruction should be sought.

• Early closure of the aortic valve (AV) on M-mode echocardiography (echo) is a nonspecific finding that may be present with either fixed or dynamic LVOTO.

• Step 4: If significant SAM is present, assess mitral leaflets and subvalvular anatomy.

• HCM can be associated with abnormalities in papillary muscle anatomy.

• Features that predispose to LVOTO include elongated mitral leaflets, chordal slack, direct insertion of the papillary muscle into the mitral leaflets, septal chordal attachments, and anteriorly or apically displaced papillary muscles.

TABLE 13-2 ECHOCARDIOGRAPHIC FEATURES OF CARDIOMYOPATHIES

Figure 13-4 Apical long axis view of a patient with outflow tract obstruction due to systolic anterior motion of the mitral valve (MV) leaflets.

Figure 13-5 M-mode at the level of the MV tips showing septal hypertrophy and systolic anterior motion of the mitral apparatus in a patient with HCM.

Physiologic Data

• Step 1: Assess the presence and severity of intracardiac obstruction.

• Obstruction can occur at either the midventricular or left ventricular outflow tract (LVOT) level.

• Midventricular obstruction predisposes to apical aneurysm formation and scarring; contrast agents should be considered if the apex is not well visualized.

• Changes in left ventricular geometry can alter intracardiac flow patterns, dragging the mitral leaflets anteriorly into the LVOT.

• Anterior movement of the tips of the mitral leaflets may result in a loss of coaptation and posteriorly directed mitral regurgitation (MR).

• This LVOTO is a complex, dynamic process that is affected by LV contractility, loading conditions, and both mitral leaflet and subvalvular anatomy.

• Step 2: Measure the velocity of blood flow down the length of the LV using pulsed wave (PW) Doppler.

• Marching the PW Doppler sample from apex to base allows localization of the site of obstruction.

• Anterior displacement of the mitral leaflets causes associated MR to originate more anteriorly, and thus care must be taken to differentiate LVOT flow from regurgitation flow.

• Resting LVOT velocities greater than 5 m/s are uncommon and should be confirmed by finding a separate, even higher velocity (>7 m/s) mitral regurgitant jet.

• Dynamic obstruction may produce a characteristic dagger-shaped, late-peaking Doppler waveform (Fig. 13-6A); however, complete LVOTO may produce a characteristic “lobster claw” appearance (Fig. 13-6B).

• Step 3: Assess changes in LVOT velocity with provocation in adults and older children.

• Perform in patients with known or suspected HCM without resting LVOTO.

• Provocation can unmask resting LVOT gradients; patients with provocable LVOTO are more likely to have exercise-induced obstruction.

• Common provocative factors include Valsalva maneuver, pharmacologic agents (amyl nitrate or isoproterenol), and exercise.

• Step 4: Assess MR.

• MR can be difficult to quantify because of its timing (originating in mid to late systole) and eccentricity, making proximal isovelocity surface area (PISA) calculations less reliable.

• If the mitral regurgitant jet is not posteriorly directed, other etiologies for the MR should be suspected.

• Step 5: Assess diastolic function.

• Assessment of diastolic function in HCM patients is challenging due to asymmetrical hypertrophy and changes in calcium kinetics.

• Because of the asymmetrical hypertrophy, mitral annular relaxation velocities should be sampled from the septal, lateral, anterior, and inferior aspects of the annulus, with an average velocity used to assess global diastolic function.

• The ratio of mitral inflow velocity deceleration (E wave) to early mitral annular relaxation (E′) velocity is not as robust a predictor of filling pressure as in other conditions.

• Abnormalities in diastolic relaxation can precede the development of hypertrophy in patients carrying otherwise subclinical sarcomeric gene mutations (Fig. 13-7).

• Step 6: Assess consequences of HCM.

• Assess left atrial enlargement.

• Assess pulmonary artery pressures (PAPs).

• Assess right ventricular function and hypertrophy.

Figure 13-6 Complete LVOTO may result in a “lobster claw” appearance of the pulsed wave (PW) Doppler (A); more commonly, a characteristic dagger-shaped, late-peaking continuous wave (CW) Doppler signal is seen (B).

Figure 13-7 Septal mitral annular tissue Doppler sample in a carrier of a known HCM gene mutation before the development of left ventricular hypertrophy (LVH). In this patient, the myocardial early relaxation velocity is markedly decreased.

Alternate Approaches

• Exercise echo is particularly useful in evaluating patients with suspected exercise-induced LVOTO.

• Cardiac magnetic resonance imaging (MRI) is useful for determining maximal wall thickness, and the use of delayed gadolinium enhancement can provide assessment of the extent of fibrosis.

• Consider the use of contrast agents for better visualization of the left ventricular apex in patients with midcavitary obstruction.

• 3D TEE can aid in the assessment of subvalvular architecture and the location of intracardiac obstruction.

Key Points

• HCM can present with asymmetric hypertrophy of any cardiac segment, and may also manifest as concentric hypertrophy.

• The presence of LVOTO is neither necessary nor sufficient to diagnose HCM.

• When LVOTO is present, care must be taken to differentiate the LVOT Doppler signal from MR.

• Abnormalities in mitral valve and papillary muscle anatomy are common in HCM and can predispose to LVOTO.

Dilated Cardiomyopathy

• Dilated cardiomyopathy (DCM) is characterized by spherical enlargement of the LV with reduction in global systolic function. Four-chamber enlargement and dysfunction are often present (Fig. 13-8).

• Echo is an essential component of diagnosing and managing patients with DCM.

• DCM is often classified as ischemic (due to coronary artery disease) or nonischemic, based on the presence or absence of myocardial ischemia or infarction. Potential causes of DCM are listed in Table 13-3.

• Most cases of primary DCM in children are idiopathic, but a positive family history is present in 30% of cases, suggesting a genetic component.

• Anomalous origin of the left coronary artery from the pulmonary artery (ALCAPA) can present with DCM in the first weeks of life due to decreasing PAP and resultant myocardial ischemia.

• Chamber enlargement can lead to annular dilation and leaflet tethering of the semilunar valves, causing secondary (functional) valve regurgitation.

• In contrast, a primary valvular cardiomyopathy (CM) should be suspected when significant aortic regurgitation (AR) is present in the setting of DCM.

• Diastolic dysfunction is commonly present in patients with impaired systolic function, with increase in LV filling pressures.

• Important sequelae of DCM include atrial enlargement, pulmonary hypertension, ventricular aneurysm formation, and intracardiac thrombosis.

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