Elucidating the B bump on the mitral valve M-mode echogram in patients with severe left ventricular systolic dysfunction

Background: The B bump on mitral valve M-mode echogram is predictive of significant elevation of left ventricular end-diastolic pressure (LVEDP). However, its pathophysiologic mechanism remains unclear. Methods: We investigated, by means of Doppler echocardiography, the hemodynamic events that take place at late diastole in left atrium (LA) and left ventricle (LV). The study group consisted of 10 consecutive and strictly selected patients with severe dilated LV dysfunction. The noninvasive validated index used for definition of high LVEDP was the difference between the durations of atrial reverse (AR) wave in pulmonary venous flow (PVF) and atrial (A) wave in mitral flow (MF). Peak velocities of PVF and MF were measured. The time interval from ECG P wave to the end of B bump (P–B) and from P wave to the end of AR (P–AR) were measured and correlated. Mitral diastolic regurgitation (DR) was searched with M-mode color Doppler. Results: All patients presented with restrictive diastolic signs on MF and PVF. The mean value of AR time minus A time was 61±12 ms. There was a strong linear correlation between P–B and P–AR (r=0.94, p<0.001). Only five patients had DR. No patient had LV inflow during B bump. Conclusions: (1) Mitral B bump is essentially a late diastolic phenomenon in which the leaflets keep a semi-open position without LV inflow effectiveness. (2) The resultant LA pressure which prolongates the duration of AR wave beyond A wave, analogously work over mitral leaflets, pushing them toward LV generating the bump. (3) DR is caused by LVEDP higher than LA pressure and coexists with B bump without a cause–effect relationship.