**Question:** All are true about hypertrophic obstructive cardiomyopathy except -

A. Hypertrophic cardiomyopathy is a genetic disorder.
B. The left ventricular outflow tract (LVOT) is dilated in hypertrophic cardiomyopathy.
C. The hypertrophy in hypertrophic cardiomyopathy is diffuse, affecting the entire left ventricle.
D. Hypertrophic cardiomyopathy does not affect the right ventricle.

**Correct Answer:** D. Hypertrophic cardiomyopathy does not affect the right ventricle.

**Core Concept:**
Hypertrophic obstructive cardiomyopathy (HOCM) is a type of cardiomyopathy characterized by abnormal thickening (hypertrophy) of the left ventricular muscle, leading to increased wall thickness and reduced compliance. It is a genetic disorder, with mutations in sarcomeric genes such as MYBPC3 and TNNT2.

**Why the Correct Answer is Right:**
HOCM primarily affects the left ventricle due to genetic mutations in genes responsible for cardiac myosin, actin, and troponin regulation. The hypertrophy is diffuse and involves the entire left ventricle, particularly the interventricular septum. This causes severe obstruction of the left ventricular outflow tract (LVOT) during diastole, leading to symptoms and complications like heart failure, angina, and sudden cardiac death.

**Why Each Wrong Option is Incorrect:**

A. Hypertrophic cardiomyopathy is a genetic disorder, which is true. However, it affects the left ventricle, not the right ventricle.

B. The left ventricular outflow tract (LVOT) is dilated in hypertrophic cardiomyopathy, which is incorrect. Instead, it is obstructed due to the hypertrophy.

C. Hypertrophic cardiomyopathy can present with regional hypertrophy, but the statement "diffuse hypertrophy affecting the entire left ventricle" is incorrect. Regional hypertrophy typically affects the basal segments of the left ventricular wall, not the entire left ventricle.

E. The statement "hypertrophic cardiomyopathy does not affect the right ventricle" is incorrect. While the left ventricle is primarily affected, the right ventricle can also be involved in a minority of cases, albeit less severely affected than the left ventricle.

**Clinical Pearl:**
HOCM can present with complex clinical manifestations that require a comprehensive understanding of the cardiac anatomy and physiology. Patients may exhibit symptoms like exertional dyspnea, chest pain, and syncope due to the obstruction of the LVOT. Diagnosis is usually confirmed by echocardiography that shows increased wall thickness, apical hypertrophy, and the presence of a bulging interventricular septum. Medical management includes beta-blockers, calcium channel blockers, and in severe cases, surgical myectomy or alcohol septal ablation may be considered.