**3. Hypertrophic cardiomyopathy**

### **3.1 Introduction**

This condition has been called asymmetric septal hypertrophy (ASH), hypertrophic obstructive cardiomyopathy (HOCM), dynamic muscular subaortic stenosis, idiopathic hypertrophic subaortic stenosis (IHSS), diffuse muscular subaortic stenosis, Brock's Disease, Teare's Disease, and others, but is now best described as hypertrophic cardiomyopathy. HCM is a primary, often inherited, disease of the myocardium affecting the sarcomeric proteins. This results in hypertrophy and disorganization of myofibrils and fibrosis of interstitia. Autosomal dominant inheritance with a high degree of penetrance is noted. Matrilineal, X-linked, and autosomalrecessive inheritance patterns have also been described. One hundred or more different mutations in 10 genes have been discovered (chromosomes 1, 14 & 15). Troponin-T, beta myosin heavy chain, and alpha tropomyosin may also be involved.

### **3.2 Pathology and pathophysiology**

HCM is characterized by hypertrophy of the left ventricle (more often) and/or right ventricle (RV). Concentric left ventricular (LV) hypertrophy is present without an identifiable hemodynamic reason. Frequently, there is asymmetric interventricular septal hypertrophy. Diastolic dysfunction including, delayed relaxation and increased muscle stiffness are present. LV outflow obstruction, which is dynamic is seen in 25% of cases. Systolic anterior motion (SAM) of the mitral valve may contribute to the LV outflow tract narrowing. RV outflow obstruction is rare but is more frequent in infants with HCM. There appear to be areas of localized hypertrophy in the LV muscle in addition to those in the septum and serve as potential arrhythmogenic foci.

#### **3.3 Symptoms**

There are usually no symptoms in infants and children; they are most often detected because of a cardiac murmur or family history of HCM. Symptoms in infancy usually indicate a poor prognosis. In early adulthood, the presenting symptoms are exertional dyspnea, lightheadedness, chest pain, syncope, or palpitations.
