septal hypertrophy

The two main pumping chambers share a common dividing wall, the interventricular septum. Septal hypertrophy is thickening of that wall, and because the septum forms one side of the channel through which blood leaves the left ventricle, thickening there can crowd that exit passage in a way that thickening elsewhere does not.

It is a defining feature of many cases of hypertrophic cardiomyopathy, where the septum is often disproportionately thick compared with the rest of the wall — so-called asymmetric septal hypertrophy. As the heart contracts, a markedly thickened septum can bulge into the outflow tract and, together with abnormal motion of the mitral valve, partly block the path of ejected blood, producing left ventricular outflow tract obstruction and a murmur.

Septal thickening can also occur for other reasons, such as long-standing high blood pressure, so finding it does not by itself diagnose a specific disease. Doctors measure its thickness on echocardiography or MRI, assess whether it causes obstruction, and weigh it alongside symptoms, family history, and rhythm risk. When severe and obstructive, it can be treated by medication, an alcohol-injection procedure, or surgical removal of muscle (septal myectomy).