Hypertrophic Cardiomyopathy: Genetics, Pathogenesis, Diagnosis, Clinical Course and Therapy

Abstract

Hypertrophic cardiomyopathy (HCM) is a genetic disorder of cardiac myocytes that is characterized by cardiac hypertrophy, unexplained by the loading conditions, a non-dilated left ventricle and a normal or increased left ventricular ejection fraction (LV-EF). Prevalence of HCM has been estimated at 0.16% to 0.29% (≈ 1:625–1:344 individuals) in the general adult population. HCM represents the most common genetic heart disease and represent an archetypical single gene disorder with an autosomal dominant pattern of inheritance and historically termed a “disease of the sarcomere”. The precise mechanisms by which sarcomere variants result in the clinical phenotype have not been fully understood. Mutant sarcomere genes trigger several myocardial changes, leading to hypertrophy and fibrosis, which ultimately result in a small, stiff ventricle with impaired systolic and diastolic performance despite a preserved LV-EF. The most common differential diagnosis challenges in the presence of hypertrophic heart disease are represented by: athlete’s heart, hypertensive heart and other cardiomyopathies mimicking HCM. A multimodality approach using ECG, echocardiography, CMR, cardiac computed tomography (CCT) and cardiac nuclear imaging provides unique information about diagnosis, staging and clinical profiles, anatomical and functional assessment, metabolic evaluation, monitoring of treatment, follow-up, prognosis and risk stratification, as well as preclinical screening and differential diagnosis. HCM may be associated with a normal life expectancy and a very stable clinical course. However, about a third of patients develop heart failure (HF); in addition, 5–15% of cases show progression to either the restrictive or the dilated hypokinetic evolution of HCM, both of which may require evaluation for cardiac transplantation. The clinical course of HCM has been classified into four clinical stages: non-hypertrophic, classic, adverse remodeling and overt dysfunction phenotype. No evidence-based treatments are available for non-hypertrophic HCM patients (pre-hypertrophic stage), on the other hand in classic HCM, adverse remodeling and overt dysfunction phenotype, pharmacological or interventional strategies have the target to improve functional capacity, reduce symptoms, prevent disease progression. Therapeutic approach mainly differs on the basis of the presence or absence of significant obstructive HCM. Adult patients with HCM report an annual incidence for cardiovascular death of 1–2%, with sudden cardiac death (SCD), HF and thromboembolism being the main causes of death; the most commonly recorded fatal arrhythmic event is spontaneous ventricular fibrillation. For this reason, SCD risk estimation is an integral part of clinical management of HCM. International guidelines suggest the evaluation of several risk factor for SCD based on personal and family history, non-invasive testing including echocardiography, ambulatory electrocardiographic 24 hours monitoring and CMR imaging in order to identity those patients most likely to benefit implantable cardioverter-defibrillator (ICD) implantation. The present chapter summarize genetics, pathogenesis, diagnosis, clinical course and therapy of HCM as well as novel therapeutic options.