How does hypertrophic obstructive cardiomyopathy (HOCM) typically cause a murmur?

Hypertrophic obstructive cardiomyopathy (HOCM) typically causes a murmur due to asymmetrical left ventricular hypertrophy, which leads to outflow obstruction. In HOCM, the heart muscle becomes abnormally thickened, particularly in the interventricular septum. This thickening can encroach upon the left ventricular outflow tract (LVOT), creating a dynamic obstruction during systole when the left ventricle contracts.

As the left ventricle contracts, the hypertrophied septum can disrupt the normal flow of blood through the aortic valve, often generating a characteristic systolic murmur that can be heard best along the left sternal border. This murmur is typically worse with maneuvers that decrease venous return to the heart, such as standing up or performing a Valsalva maneuver, as they can accentuate the outflow tract obstruction caused by the hypertrophy.

Understanding this mechanism provides insight into the functional consequences of HOCM and the auscultatory findings associated with the condition. The murmur is not primarily due to increased blood flow through a normal valve, valve stenosis, or simply an increased ventricular size during systole, making this reasoning robust in identifying the cause of the murmur