SeminarHypertrophic cardiomyopathy
Section snippets
Nomenclature, definition and prevalence
HCM has been known by a confusing multitude of names, largely reflecting its heterogeneity, with many individual investigators characterising the disease on the basis of the most obvious clinical feature apparent in a particular cohort of patients.1, 2 There has even been uncertainty as to whether HCM is best regarded as a single but diverse disease entity, or rather as a group of related and phenotypically similar disorders.
HCM has become the preferred name because, unlike many other terms
Genetic defects
HCM is a mendelian trait with an autosomal dominant pattern of inheritance. Over the past few years, laboratory and clinical studies have defined several gene mutations that cause HCM, and in the process have provided further evidence for the heterogeneity of the disorder.3, 5, 9 HCM can be caused by several mutations in any one of four genes that encode proteins of the cardiac sarcomere: β-myosin heavy-chain gene on chromosome 14; cardiac troponin T on chromosome 1; α-tropomyosin on chromosome
Left-ventricular hypertrophy
In HCM, the distribution of hypertrophy (at end-diastole) is almost always asymmetrical (figure 1), but there is substantial structural diversity, and no particular phenotypic expression of HCM can be regarded as “classic” or typical of the overall disease.6 Absolute left-ventricular wall thicknesses in clinically identified patients range broadly from mildly increased (13–15 mm; normal ≤12 mm) to massively increased, including the most substantial hypertrophy observed in any cardiac disease
Pathophysiology
The symptoms of HCM include most prominently those of pulmonary congestion (exertional dyspnoea, fatigue, orthopnoea, and paroxysmal nocturnal dyspnoea), and chest pain, which may be typical of angina. However, impaired consciousness (syncope, near-syncope, or lightheadedness) and palpitations are also commonly involved. Because the pathophysiology of HCM is complex and incompletely defined, the precise mechanisms by which each of these symptoms occur in all patients are not entirely resolved.
Natural history and treatment
HCM is a unique disease by virtue of its clinical expression in all phases of life from infancy to old age. The natural history is typically variable.1, 2, 7, 25, 28, 29, 30, 31, 32 Although clinical course is generally stable over long periods, it can be punctuated by adverse clinical events, including periodic or progressive symptoms of heart failure, sudden cardiac death, and peripheral embolisation.25, 28, 29, 30, 31
Full appreciation of the clinical implications of HCM requires an awareness
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