Hypertrophic cardiomyopathy (HCM) is a genetically determined cardiac disorder characterized by hypertrophy, often of the left ventricle (LV), with non-dilated ventricular chambers and no other cardiac, systemic or metabolic disease (eg aortic stenosis, thyroid disease or hypertension) capable of producing the extent of hypertrophy manifested by the patient
Maximal end-diastolic LV wall thickness of ≥15 mm in adults, or body surface area adjusted z-score of ≥2 standard deviations above the mean for age, sex or body size in children
For the diagnosis of early HCM in children, a threshold of a z-score >2.5 may be used in asymptomatic children without family history and a threshold of a z-score >2 for children with a family history or a positive genetic test
Results from mutations in one of the cardiac sarcomere protein genes that encode the parts of the apparatus for contraction: Actin, tropomyosin alpha-1 chain, myosin binding protein C, troponin I, troponin T, beta myosin heavy chain, essential and regulatory light chains
Most common genes in patients with HCM and a pathogenic sarcomeric gene variant are beta myosin heavy chain 7 (MYH7) and myosin-binding protein C3 (MYBPC3)
Epidemiology
The most common form of genetic cardiovascular disorder occurring in one out of 500 individuals regardless of gender or race
Presents in all age groups: Prevalence is 0.2% in adults and 0.029% in children
An autosomal dominant inherited disorder, affected heterozygous individuals beget children with a 50% risk (equal risk for both males and females) of having the gene mutation
Phenotype is abnormal, frequently focal, hypertrophy that leads to atrial and ventricular arrhythmia, diastolic dysfunction, mitral regurgitation, dynamic LV outflow tract obstruction (LVOTO), pulmonary hypertension, myocardial ischemia, coronary insufficiency and congestive heart failure
Pathophysiology also consists of metabolic and energetic abnormalities and potential autonomic dysfunction
Signs and Symptoms
Symptoms can range from patients being asymptomatic to mildly or significantly symptomatic with pre-syncopal or syncopal episodes, palpitations, chest pain, decreased exercise tolerance, symptoms of pulmonary congestion (eg fatigue, dyspnea, orthopnea and paroxysmal nocturnal dyspnea) and symptoms of end-stage heart failure or cardiac arrest
Life expectancy is normal or near-normal in most patients with HCM though without possibility of remission; mortality is often due to embolic stroke, heart failure with sudden cardiac death
