The M-mode echocardiogram shows eccentric valve closure in diastole. Systolic opening of the valve is good.
Eccentricity index for a bicuspid aortic valve is calculated as follows :
1/2 of aortic lumen diameter divided by minimum distance of diastolic cusp echo from nearest aortic margin
The measurement is illustrated in the image below:
The diastolic diameter of the aorta is represented by A. Half of it is taken for the calculation of eccentricity index. B represents the minimum distance of diastolic cusp echo from nearest aortic margin. In the study by Nanda NC et al , the eccentricity index was low (1.0 to 1.25) in trileaflet valves. Eccentricity index ranged from 1.5 to 5.6 with mean of 2.43 in those with bicuspid aortic valves.
Central closure line of the aortic valve in a trileaflet valve is shown below for comparison:
If the eccentricity index is calculated for this trileaflet valve, it will be close to 1.
Two dimensional image with bicuspid aortic valve in open position is given below:
Two obliquely oriented leaflets are seen in open position. In case of trileaflet valve, three leaflets will be seen.