What is the significance of a mitral B-bump seen on M-mode?

The mitral B-bump on M-mode echocardiography represents a distinct anterior motion or thickening of the anterior mitral leaflet during atrial systole. It is associated with elevated left atrial systolic pressure.

The B-bump is a marker of increased left atrial pressure transmitted to the mitral valve, often seen in diastolic dysfunction and conditions causing elevated left atrial pressure.

It is not a direct indicator of left ventricular end-diastolic pressure, hypertrophic obstructive cardiomyopathy, or mitral stenosis.

This phenomenon is described in the "Textbook of Clinical Echocardiography, 6e", Chapter on Diastolic Function and Mitral Valve Motion【20:215-220†Textbook of Clinical Echocardiography】.