Abstract and Introduction
Abstract
Hypertrophic cardiomyopathy (HCM) is a genetic disease characterized by abnormal myocardial hypertrophy, which can lead to a wide clinical spectrum, including sudden cardiac death and heart failure. Cardiac MRI has a significant role in establishing the diagnosis of HCM. In the three principal management issues related to HCM; testing of family members of affected individuals; assessing the risk of sudden cardiac death from lethal ventricular arrhythmias; and selection of appropriate treatments for left ventricular outflow obstruction, cardiac MRI has established or emerging roles.
Introduction
Hypertrophic cardiomyopathy (HCM) is a genetic disorder characterized by a myocardial wall thickness of ≥15 mm in the absence of secondary causes such as systemic hypertension, aortic valve stenosis, glycogen storage diseases (e.g., Fabry's disease), infiltrative cardiomyopathy (e.g., amyloidosis) or athlete's heart. HCM affects approximately one in 500 individuals and is a major cause of sudden cardiac death (SCD), particularly in young adults. While many potential genetic mutations have been discovered that are transmitted in an autosomal dominant manner, the general abnormality is typically related to an alteration of one of the contractile proteins in the myocardial sarcomere. Although genetic testing is available, its yield is modest (~30–60% detection rate) and dependent on a variety of factors, including phenotypic expression. While genetic testing may be valuable for screening relatives when a mutation is detected, screening for the phenotype is required in families in which the proband does not have a pathogenetic mutation.
Many HCM patients demonstrate a similar natural history to individuals in the general population without HCM. However, selected patients may be at excessive risk of SCD from lethal ventricular arrhythmias or severe left ventricular (LV) outflow tract (LVOT) obstruction. Although risk stratification for SCD should be individualized, there is strong evidence to suggest a benefit of an implantable cardiac defibrillator (ICD) in high-risk patients with HCM. Despite enhanced understanding of the pathophysiology of disease and prediction classifications, risk stratification and potential therapeutic strategies, technological advances in cardiac magnetic resonance imaging (CMRI) may provide additional and incremental information for establishing the diagnosis and providing improved risk stratification. An updated HCM guideline statement was recently published highlighting major and minor risk factors for predicting SCD.Box 1 highlights the established and potential risk factors for SCD in HCM.
Finally, decisions regarding medical or septal reduction therapy are highly dependent on symptom severity, morphology (particularly of the interventricular septum) and physiologic measures of LVOT gradient, and associated mitral regurgitation, and diastolic LV function. CMRI has established or emerging roles in each of these key management decision points.