Hypertrophic cardiomyopathy is most commonly due to hypertrophy of which structure, and which heart sound is commonly associated?

• A. Left ventricular free wall; S4
• B. Cardiac septum; S4
• C. Right ventricular outflow tract; S3
• D. Atrial septum; S1

Answer: (B)

Hypertrophic cardiomyopathy most often shows asymmetric thickening of the interventricular septum, leading to a thickened septum rather than uniform left ventricular wall thickening. This septal hypertrophy narrows the left ventricular outflow tract and makes the ventricle less compliant, contributing to diastolic dysfunction.

Because the ventricle becomes stiff, the atria must contract against a noncompliant ventricle, which produces an S4 gallop. S4 is the classic sound associated with hypertrophic changes and reduced ventricular compliance.

Other patterns of hypertrophy or sounds don’t fit as well: hypertrophy limited to the right ventricular outflow tract isn’t the typical site for classic HCM, and an S3 would more likely point to systolic dysfunction with dilated ventricles rather than the stiff, hypertrophied ventricle seen in HCM. S1 is a normal part of the first heart sound and is not specific to this condition.