All are true about hypertrophic obstructive cardiomyopathy except
**Core Concept**
Hypertrophic obstructive cardiomyopathy (HOCM) is a genetic disorder characterized by abnormal thickening of the heart muscle, particularly affecting the left ventricle. This thickening leads to impaired diastolic function and potential obstruction of the left ventricular outflow tract (LVOT). The underlying pathophysiology involves mutations in genes encoding sarcomeric proteins, which disrupt the normal contractile function of the heart muscle.
**Why the Correct Answer is Right**
The correct answer will be identified by understanding the characteristic features of HOCM. In HOCM, the thickened heart muscle can cause dynamic LVOT obstruction, particularly during exercise or with conditions that increase contractility, such as anxiety or a hot shower. This obstruction can lead to symptoms like chest pain, shortness of breath, and syncope. The characteristic echocardiographic finding in HOCM is a thickened left ventricular septum with a narrow LVOT, often accompanied by a systolic anterior motion (SAM) of the mitral valve.
**Why Each Wrong Option is Incorrect**
**Option A:** The statement that HOCM is caused by a viral infection is incorrect, as HOCM is a genetic disorder resulting from mutations in sarcomeric genes. While viral infections can trigger the onset of symptoms in some cases, the underlying cause is not a viral infection.
**Option B:** The assertion that HOCM is characterized by a dilated left ventricle is incorrect, as HOCM is marked by a thickened and non-dilated left ventricle.
**Option C:** The claim that HOCM is a form of coronary artery disease is incorrect, as HOCM is a primary cardiac muscle disorder unrelated to coronary artery disease.
**Clinical Pearl / High-Yield Fact**
The "Nutmeg sign" on echocardiography, characterized by a triangular or "nutmeg-like" appearance of the left ventricular septum, is a classic echocardiographic finding in HOCM. This sign is associated with a thickened septum and is often seen in conjunction with SAM of the mitral valve.
**Correct Answer:** B.