Hypertrophic cardiomyopathy. Incidence of hypertrophic cardiomyopathy may vary from 0.02 to 0.2% in the general population. It is characterised by a hypertrophied and non-dilated left ventricle with a small cavity.
The hallmark of HCM is asymmetric septal hypertrophy (ASH) which narrows the left ventricular outflow tract (LVOT) and produces the systolic anterior motion of mitral valve (SAM) due to the Venturi effect.
HCM may present with concentric left ventricular hypertrophy as well as apical cardiomyopathy with hypertrophy of left ventricular apex and adjacent myocardium.
Familial hypertrophic cardiomyopathy: HCM has an autosomal dominant pattern of inheritance, with involvement in 50% of first degree relatives. Several genes on multiple chromosomes and many mutations have been identified. Chromosome 14 (myosin), chromosome 1 (troponin T), and chromosome 15 (tropomyosin) are some of the loci identified.
Pathophysiology of HCM: Pathophysiologic abnormality in systole is the dynamic LVOT gradient, which increases on standing and in situations which reduce the afterload of the left ventricle. Diastole is marked by impaired diastolic filling, with elevated filling pressures due to impaired relaxation of the hypertrophied ventricle.
Atrial booster function is very important in this situation and loss of atrial booster function due to atrial fibrillation will lead to rapid hemodynamic deterioration.
Myocardial ischemia can occur in HCM due to various mechanisms like increased muscle mass, filling pressure and oxygen demand; decreased vasodilator reserve and capillary density; abnormal intramural coronary arteries and systolic compression of coronary arteries.
Clinical Manifestations of HCM: HCM can be totally asymptomatic being detected by echocardiographic findings during family screening or after a routine ECG which shows gross left ventricular hypertrophy pattern. Symptomatic cases may present with dyspnea on exertion, angina pectoris, fatigue, presyncope or syncope.
Palpitations, paroxysmal nocturnal dyspnoea or feature of congestive heart failure can be the presenting features in some cases. There is an increased risk of sudden cardiac death (SCD) in children and adolescents with HCM.
Natural History of HCM: Hypertrophic cardiomyopathy has an annual mortality rate of 1-3%. The risk of SCD is higher in children and may be as high as 6% per year.
Clinical deterioration is usually slow in HCM. Progression to dilated phase may occur in 10-15% cases of HCM. The higher left ventricular wall thickness on echocardiography and left ventricular hypertrophy with strain pattern may help in differentiation from dilated cardiomyopathy.
Risk Factors for SCD in hypertrophic cardiomyopathy: Young age (less than 30 years), malignant family history of SCD, certain gene mutations prone to SCD, aborted SCD, sustained ventricular tachycardia, recurrent syncope and septal thickness more than 30 mm are considered to be risk factors for sudden cardiac death in hypertrophic cardiomyopathy.
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