Fig. 14.1
Dynamic LVOT obstruction. Asymmetric septal HCM with systolic anterior motion (SAM) in a 74-year-old man who presented with chest tightness. (a) Schematic illustration of LVOT obstruction. (b) Four-chamber SSFP cine MR images show systolic anterior motion (SAM) of the anterior mitral valve leaflet (arrows) accompanied by a signal void jet flow into the LVOT. There is also a jet of mitral regurgitation (arrowheads) into a moderately enlarged left atrium
Dynamic LVOT is usually due to systolic anterior motion of the anterior leaflet of the mitral valve (SAM) with mid-systolic contact with the ventricular septum.
SAM is not pathognomonic of HCM, as it may present in patients with hypertensive heart, diabetes mellitus, acute myocardial infarction, and mitral valve repair or dysfunction.
Anomalous insertion of the papillary muscles (heads of papillary muscles insert directly ventricular aspect of mitral leaflet) can occur in 13 % of patients with HCM and can contribute LVOT obstruction.
14.2.2 Diastolic Dysfunction
Diastolic dysfunction arises from ventricular relaxation and chamber stiffness.
Ventricular relaxation results from the systolic contraction load caused by LVOT obstruction and delayed inactivation caused by abnormal intracellular calcium reuptake.
Chamber stiffness is caused by severe LVH.
14.2.3 Myocardial Ischemia
Myocardial hypertrophy and extracellular fibrosis predispose to increased left ventricular stiffness which in concert with compromised cellular energetics and abnormal calcium handling lead to diastolic dysfunction.
Abnormal dysplasia of small intramural coronary arteriole caused by increased pressure from adjacent hypertrophied myocytes causes myocardial ischemia.
14.2.4 Mitral Regurgitation
Interleaflet gap (anterior leaflet motion is greater than that of the posterior leaflet) during SAM resulting in a posteriorly directed jet of mitral regurgitation
Besides SAM, intrinsic valvular abnormalities (i.e., mitral valve prolapsed, leaflet thickening secondary to injury from repetitive septal contact, chordal rupture or elongation, etc.) were the cause of mitral regurgitation.
14.3 Role of Each Diagnostic Modalities for HCM
Because the clinical presentation is nonspecific and diverse, noninvasive imaging techniques play a pivotal role in detecting the disease and understanding its pathophysiology. The goals of noninvasive imaging for HCM are to distinctly diagnose the disease along with characterization of its phenotype, to assess the cardiac function (including presence of dynamic obstruction), to classify the disease severity and risk stratification, and to serve as a screening tool for the family and as a guide for appropriate therapy (Table 14.1) [4].
14.3.1 Cardiac Structure
Characterization of the presence, location, and extent of LVH should be needed for all segment of the entire myocardium.
One third of patients with HCM have RVH, thus RV wall thickness and mass also should be needed to assess.
Intrinsic structural abnormalities of the mitral valve apparatus and papillary muscle number and location were also evaluated.
14.3.1.1 Echocardiography
Transthoracic echocardiography (TTE) is widely used for the initial evaluation of all patients with suspected HCM (Class I, Level of Evidence B).
Echocardiography has a limitation of operator and sonic window dependency; it is sometimes unable to define the endocardial border, especially the anterolateral free wall of the left ventricle (LV) in the parasternal short-axis view and apex.
The degree of LVH could be underestimated by echocardiography, which, in fact, can delay proper treatment, thereby failing to prevent a SCD.
14.3.1.2 MRI
CMR has strength of 3D imaging technique with high spatial and temporal resolution useful for detection of focal LVH which may not be well visualized by 2D echocardiography.
SSFP cine MRI sequence produces sharp contrast between the bright blood pool and the dark myocardium, including accurate wall thickness and mass measurements with high reproducibility.
CMR is indicated in patients with suspected HCM when echocardiography is inconclusive for diagnosis (Class I, Level of Evidence B).
CMR is reasonable in patients with HCM to define apical HCM and/or aneurysm if echocardiography is inconclusive (Class IIa, Level of Evidence B).
14.3.1.3 MDCT
MDCT has higher spatial resolution over MRI and echocardiography; it is at least equivalent or more likely superior with respect to HCM phenotype (LV thickness, volume, EF, mass, etc.).
MDCT provides complete tomographic coverage of the entire myocardium because of isotropic imaging; it can well assess all cardiac structures including papillary muscles.
MDCT may be reasonable in the patient who has contraindicated CMR (i.e., pacemaker or IDC implantation, claustrophobia, etc.) or when patients cannot hold their breath for long periods.
14.3.2 Assessment of LV Systolic and Diastolic Function
14.3.2.1 Echocardiography
Echocardiography is a validated method for a comprehensive approach of systolic and diastolic function including LA and LV filling pressure.
TTE is useful for myocardial function (Class IIa, Level of Evidence C).
14.3.2.2 MRI
CMR measurements of systolic function including ventricular volumes and EF are validated with high diagnostic accuracy and high reproducibility.
CMR can measure mitral inflow, the pulmonary vein, and LV filling.
14.3.2.3 MDCT
CT provides an accurate assessment of systolic function including LV volume and EF.
CT is not indicated for the assessment of LV diastolic function due to limited temporal resolution than MRI or echocardiography.
14.3.3 Dynamic LVOT Obstruction and Mitral Valve Abnormalities
14.3.3.1 Echocardiography
Echocardiography is an initial modality for LVOT obstruction or mitral regurgitation.
Exercise TTE can be useful in the detection and quantification of dynamic LVOT obstruction (Class IIa, Level of Evidence B).
14.3.3.2 MRI
Cine MRI can accurately identify the presence of mitral-septal contact and regurgitant signal void jet.
Velocity encoding (VENC) sequence can measure the peak velocity through the LVOT.
However, it has limited that CMR-derived velocities can be assessed only under basal conditions, because one third of patients with HCM have LVOT obstruction only during provocation.
14.3.3.3 MDCT
CT is not indicated for dynamic obstruction of mitral regurgitation although it can well evaluate the papillary muscle or mitral valve apparatus.
14.3.4 Myocardial Ischemia
14.3.4.1 Echocardiography
In general, there is a limited role for echocardiography in diagnosing myocardial ischemia, although regional wall motion abnormality is an indirect finding for ischemia.
14.3.4.2 MRI
Stress perfusion MRI permits accurate qualitative and quantitative assessment of myocardial blood flow at rest and during pharmacologic stress, with superior spatial resolution to PET.
The severity of perfusion impairment in HCM is correlated with the degree of LVH.
14.3.4.3 MDCT
In patients with HCM with coexistent epicardial coronary disease, because epicardial coronary disease is one of the several etiologic mechanisms that contribute to myocardial ischemia in patients with HCM, it can be difficult to interpret whether ischemia is caused by HCM or by decreased coronary flow reserve.
Cardiac MDCT can provide useful information for the noninvasive assessment of coexistent epicardial coronary disease in patients with HCM [5].
14.3.5 Myocardial Fibrosis
14.3.5.1 Echocardiography
Large areas of regional fibrosis can lead to segmental dysfunction manifested by reduced strain. However, it is limited for its low specificity for fibrosis.
14.3.5.2 MRI
Late delayed gadolinium-enhancement (LGE) MRI techniques can provide unique information on tissue characterization, specifically for the identification of myocardial fibrosis or scarring.
Areas of LGE can be measured and the amount quantified and expressed as a percentage of total LV mass.
The prevalence of LGE in HCM is approximately 50–70 % and when present occupies on average 10 % of the overall LV myocardial volume.
The location of LGE is common at the confined area to only the LV free wall or insertion points of the RV free wall and ventricular septum. In addition, LGE tends to locate in segments with hypertrophy or with large LV mass.
However, it still remains uncertain whether all LGE in patients with HCM with normal or hyperdynamic EF represents myocardial fibrosis.
CMR may be considered for risk stratification with late gadolinium enhancement (LGE) and differential diagnosis from other infiltrative disease including cardiac amyloidosis or Fabry disease (Class IIb, Level of Evidence C).
14.3.5.3 MDCT
CT has no role at the present time for the evaluation of myocardial fibrosis.
Table 14.1
Relative merits of each noninvasive imaging for the assessment of hypertrophic cardiomyopathy
Echocardiography
MDCT
MRI
LV volume
+++
++
++++
LV hypertrophy
+++
++++
++++
Ejection fraction
+++
+++
++++
Regional function
+++
++
++++
LV filling pressure
+++
–
++
PA pressure
+++
–
+++
Dynamic obstruction
+++
+
+++
Mitral regurgitation
+++
–
++
Ischemia/CFR
+
–
++
Monitoring of therapy
+++
+
+++
Tissue characterization
++
+
++++
Preclinical diagnosis
++
+++
+++
14.4 Classification of HCM by Phenotypes
The usual diagnostic criterion for HCM is a maximal LV wall thickness greater than or equal to 15 mm on end-diastolic phase.< div class='tao-gold-member'>Only gold members can continue reading. Log In or Register to continue
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
