Fig. 26.1
Axial image (left) and 3D color-coded image (right) from a cardiac CTA show marked thickening of the left ventricular muscle, especially the interventricular septum (A), which narrows the left ventricular outflow tract (B) in a patient with hypertrophic cardiomyopathy
Delayed enhancement due to gadolinium accumulating in areas of fibrosis (Fig. 26.2)
Fig. 26.2
Delayed enhancement images on a cardiac MRI perfusion study show marked hypertrophy of the wall of the left ventricle with enhancement of the interventricular septum (black arrows). This delayed enhancement is typically due to fibrosis and scarring in patients with hypertrophic cardiomyopathy
26.2 Imaging
Imaging in patients with HCM has several goals:
Diagnose disease and characterize phenotype
Assess cardiac function, including the presence or absence of dynamic obstruction
Classify disease severity and risk stratification
Provide therapy guidance, including procedural localization, posttreatment monitoring of residual obstruction, and postprocedural assessment of morphology and function
Several general features are diagnostic:
Any aspect of the LV wall with maximal thickness greater than or equal to 15 mm in end-diastole; LV thickness greater than 30 mm is a risk factor for sudden cardiac death
Ratio of septal to basal LV wall thickness at the midventricular level greater than 1.5 for asymmetric HCM
Ratio of apical to basal LV wall thickness of 1.3–1.5 for apical HCM
26.2.1 Radiographic Findings
A normal chest radiograph is reported in 85 % of cases. Diffuse cardiac enlargement may be seen in later stages. Left atrial enlargement can be seen, owing to mitral valve insufficiency and diastolic dysfunction.
26.2.2 Echocardiography Findings
Primary screening tool
Effectively evaluates septum
Poorly visualizes cardiac apex and anterolateral free wall
Provides real-time visualization of anterior systolic motion of the mitral valve
Doppler used to evaluate for mitral valve regurgitation, and for LVOT or subaortic obstruction
26.2.3 MRI Findings
Steady-state free precession (SSFP) white blood cine
Evaluates LV morphology, as well as LV systolic and diastolic function
Decreased end-diastolic LV cavity size/volume
Left atrial enlargement
Anterior systolic motion of the mitral leaflets
Regional to global myocardial systolic hypokinesis as disease progresses
In end-stage or burnout phase, when patient progresses to severe systolic dysfunction, paradoxical LV dilatation and wall thinning can be seen
High-velocity jet in LVOT obstruction is represented by a high signal intensity or signal void
LVOT pressure gradient ≥ 30 mmHg at rest or ≥ 50 mmHg on provocation is risk factor for sudden cardiac death or progression to congestive heart failure
LV crypt, a V-shaped fissure or blind pit into the myocardium, has been postulated as an early MR finding in preclinical patients (as high as 81 %) with HCM gene mutation, who go on to develop HCM
Delayed gadolinium enhancement
Delay of 10–30 min after contrast injection is seen in about 80 % of patients with HCM
Accumulation of gadolinium within regions of fibrosis or scarring is a risk factor for the development of ventricular arrhythmia and sudden cardiac death
Enhancement tends to be patchy and multifocal, located within the mid myocardium, and does not correspond to a coronary artery distribution
26.2.4 Multidetector CT Findings
CT is not often used in the pediatric population because of radiation exposure, but it can effectively evaluate cardiac morphology and function and allows for the assessment of coronary arteries. Its higher spatial resolution versus MRI allows for multiplanar reconstructions, and it has three-dimensional (3D) reconstruction capability.
26.2.5 Imaging Recommendations
Echocardiography is used as a screening tool, but MRI is the optimal imaging modality, as it provides better evaluation for segmental myocardial hypertrophy, as well as assessment of LV function, LVOT obstruction, and the presence of fibrosis. MRI is also effective in differentiating HCM from other causes of cardiomyopathy and providing risk stratification.
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