ORIGINAL ARTICLE
Magnetic Resonance Imaging for Hypertrophic Cardiomyopathy Update Andy Kar Wai Chan, MD, Bhanusupriya Somarouthu, MD, and Brian Ghoshhajra, MD, MBA
Objectives: Hypertrophic cardiomyopathy (HCM) is a genetic disease of the myocardium. Although many patients remain asymptomatic, sudden cardiac death could be the first manifestation of HCM. Magnetic resonance imaging (MRI) plays an important role in the diagnosis and management of this disease. Methods: The epidemiology, pathophysiology, and diagnosis of HCM will be briefly reviewed. This is followed by a discussion on the role of cardiac MRI, recommended protocol, typical imaging findings of HCM, and advanced MRI techniques. Conclusions: Although MRI is not intended to be a first-line tool for the assessment of HCM, MRI does provide valuable information to aid the management of patients either at risk of or diagnosed with HCM. Key Words: cardiac MRI, cardiac MR, cardiac magnetic resonance imaging, cardiac magnetic resonance, hypertrophic cardiomyopathy, HCM (Top Magn Reson Imaging 2014;23: 33Y41)
H
ypertrophic cardiomyopathy (HCM) is a disease of the myocardium characterized by unexplained left ventricular (LV) hypertrophy associated with nondilated ventricular chambers in the absence of another cardiac or systemic disease.1 It is an inherited and global cardiovascular disease, with a prevalence of about 0.2% (1:500) in the general population, equivalent to about 600,000 people affected in the United States.1,2 Hypertrophic cardiomyopathy is the most common cause of sudden cardiac death (SCD) in young people. Many individuals remain asymptomatic and undiagnosed; therefore, the disease remains underrecognized in clinical practice.1,2
CLINICAL MANIFESTATIONS Hypertrophic cardiomyopathy can manifest at any age. Sudden cardiac death is the most common manifestation of HCM, with a mortality rate at about 1% per year. Other manifestations include progressive heart failure, chest pain, atrial fibrillation, and embolic stroke.2 Heart failure may or may not be associated with left ventricular (LV) outflow tract (LVOT) obstruction. In those without LVOT obstruction, failure is usually secondary to diastolic dysfunction, except in advanced (or ‘‘burned out’’) HCM where systolic dysfunction is present.2
Histologically, HCM manifests as myocyte disarray, abnormal intracellular calcium reuptake, and microvascular ischemia resulting in cell death and progressive fibrosis.2 Both the myocyte disarray and myocardial fibrosis act as foci for ventricular arrhythmia, which is the primary mechanism for SCD.2 Macroscopically, ventricular hypertrophy is evident, resulting in alterations of load and contractility of the LV. This ultimately leads to multiple interrelated abnormalities, including LVOT obstruction with or without systolic anterior motion (SAM) of the anterior leaflet of the mitral valve, mitral regurgitation, diastolic dysfunction, and myocardial ischemia due to supply-demand mismatch.1 Myocardial bridging of the left anterior descending artery (LAD) occurs more frequently in HCM than in other cardiac disorders with or without LV hypertrophy, and deep bridges (Q2 mm into the myocardium) also occur more frequently in HCM.3 However, the precise physiological significance and the risk of SCD from these bridges remain uncertain.3
DIAGNOSIS Hypertrophic cardiomyopathy is conventionally diagnosed by imaging the phenotypic expression of ventricular hypertrophy by either echocardiography or cardiac magnetic resonance imaging (MRI).1,2 A threshold of 15 mm or greater for the LV wall thickness during end diastole is commonly used in adults (or the equivalent relative to body surface area in children). The LV wall thickness in HCM patients can be massive (950 mm), with an average of about 21 to 22 mm.1,2 Several morphologic variants of HCM have been extensively described in the literature, based on the pattern of focal LV wall thickening. Asymmetrical HCM with a characteristic sigmoid-shaped upper septal contour (septal HCM) is the most common variant4,5 (Figs. 1 and 2). Other variants include apical (more common in Japanese population) (Fig. 3), midventricular (Fig. 4), mass-like, noncontiguous, symmetrical (concentric) (Fig. 5), asymmetrical HCM with reversed septal contour (Fig. 6) and HCM with right ventricular (RV) involvement (has been reported in 18% of HCM patients).2,4,5 Truly symmetrical (concentric) involvement is very rare.2 In addition to imaging the phenotypic manifestations of HCM, genetic testing is also available for definitive diagnosis and for identification of potentially affected family members.1
PATHOPHYSIOLOGY Hypertrophic cardiomyopathy is predominantly caused by either autosomal dominant or de novo mutations in genes encoding the thick and thin filament proteins of the cardiac sarcomere, with more than 1400 mutations identified.2 From the Massachusetts General Hospital, Boston, MA. Reprints: Andy Kar Wai Chan, MD, Massachusetts General Hospital, 55 Fruit Street, GRB-295 Boston, MA (e
Magnetic Resonance Imaging for Hypertrophic Cardiomyopathy Update Andy Kar Wai Chan, MD, Bhanusupriya Somarouthu, MD, and Brian Ghoshhajra, MD, MBA
Objectives: Hypertrophic cardiomyopathy (HCM) is a genetic disease of the myocardium. Although many patients remain asymptomatic, sudden cardiac death could be the first manifestation of HCM. Magnetic resonance imaging (MRI) plays an important role in the diagnosis and management of this disease. Methods: The epidemiology, pathophysiology, and diagnosis of HCM will be briefly reviewed. This is followed by a discussion on the role of cardiac MRI, recommended protocol, typical imaging findings of HCM, and advanced MRI techniques. Conclusions: Although MRI is not intended to be a first-line tool for the assessment of HCM, MRI does provide valuable information to aid the management of patients either at risk of or diagnosed with HCM. Key Words: cardiac MRI, cardiac MR, cardiac magnetic resonance imaging, cardiac magnetic resonance, hypertrophic cardiomyopathy, HCM (Top Magn Reson Imaging 2014;23: 33Y41)
H
ypertrophic cardiomyopathy (HCM) is a disease of the myocardium characterized by unexplained left ventricular (LV) hypertrophy associated with nondilated ventricular chambers in the absence of another cardiac or systemic disease.1 It is an inherited and global cardiovascular disease, with a prevalence of about 0.2% (1:500) in the general population, equivalent to about 600,000 people affected in the United States.1,2 Hypertrophic cardiomyopathy is the most common cause of sudden cardiac death (SCD) in young people. Many individuals remain asymptomatic and undiagnosed; therefore, the disease remains underrecognized in clinical practice.1,2
CLINICAL MANIFESTATIONS Hypertrophic cardiomyopathy can manifest at any age. Sudden cardiac death is the most common manifestation of HCM, with a mortality rate at about 1% per year. Other manifestations include progressive heart failure, chest pain, atrial fibrillation, and embolic stroke.2 Heart failure may or may not be associated with left ventricular (LV) outflow tract (LVOT) obstruction. In those without LVOT obstruction, failure is usually secondary to diastolic dysfunction, except in advanced (or ‘‘burned out’’) HCM where systolic dysfunction is present.2
Histologically, HCM manifests as myocyte disarray, abnormal intracellular calcium reuptake, and microvascular ischemia resulting in cell death and progressive fibrosis.2 Both the myocyte disarray and myocardial fibrosis act as foci for ventricular arrhythmia, which is the primary mechanism for SCD.2 Macroscopically, ventricular hypertrophy is evident, resulting in alterations of load and contractility of the LV. This ultimately leads to multiple interrelated abnormalities, including LVOT obstruction with or without systolic anterior motion (SAM) of the anterior leaflet of the mitral valve, mitral regurgitation, diastolic dysfunction, and myocardial ischemia due to supply-demand mismatch.1 Myocardial bridging of the left anterior descending artery (LAD) occurs more frequently in HCM than in other cardiac disorders with or without LV hypertrophy, and deep bridges (Q2 mm into the myocardium) also occur more frequently in HCM.3 However, the precise physiological significance and the risk of SCD from these bridges remain uncertain.3
DIAGNOSIS Hypertrophic cardiomyopathy is conventionally diagnosed by imaging the phenotypic expression of ventricular hypertrophy by either echocardiography or cardiac magnetic resonance imaging (MRI).1,2 A threshold of 15 mm or greater for the LV wall thickness during end diastole is commonly used in adults (or the equivalent relative to body surface area in children). The LV wall thickness in HCM patients can be massive (950 mm), with an average of about 21 to 22 mm.1,2 Several morphologic variants of HCM have been extensively described in the literature, based on the pattern of focal LV wall thickening. Asymmetrical HCM with a characteristic sigmoid-shaped upper septal contour (septal HCM) is the most common variant4,5 (Figs. 1 and 2). Other variants include apical (more common in Japanese population) (Fig. 3), midventricular (Fig. 4), mass-like, noncontiguous, symmetrical (concentric) (Fig. 5), asymmetrical HCM with reversed septal contour (Fig. 6) and HCM with right ventricular (RV) involvement (has been reported in 18% of HCM patients).2,4,5 Truly symmetrical (concentric) involvement is very rare.2 In addition to imaging the phenotypic manifestations of HCM, genetic testing is also available for definitive diagnosis and for identification of potentially affected family members.1
PATHOPHYSIOLOGY Hypertrophic cardiomyopathy is predominantly caused by either autosomal dominant or de novo mutations in genes encoding the thick and thin filament proteins of the cardiac sarcomere, with more than 1400 mutations identified.2 From the Massachusetts General Hospital, Boston, MA. Reprints: Andy Kar Wai Chan, MD, Massachusetts General Hospital, 55 Fruit Street, GRB-295 Boston, MA (e
