THE VELOCITY DISTRIBUTION IN THE AORTIC ANNULUS AT DIFFERENT TIMES DURING SYSTOLE IS MAINLY DETERMINED BY THE PATTERN OF FLOW CONVERGENCE IN THE LEFT-VENTRICULAR OUTFLOW TRACT - AN EXPERIMENTAL-STUDY USING DOPPLER COLOR-FLOW MAPPING

An experimental study in 10 open chest normal pigs (body weight: 24 +/ - 1 kg) was carried out to explore the relationship between the veloci ty distribution in the aortic annulus and the pattern of flow converge nce in the left ventricular outflow tract. The cross-sectional velocit y profiles in the aortic annulus were constructed by using Doppler col our now mapping with a previously validated time-interpolation method. The pattern of flow convergence in the left ventricular outflow tract was quantified by measuring the colour flow areas on the anterior and posterior sides of the central axis of the aortic annulus, and calcul ating their difference. The dynamic changes of the velocity distributi on, the pattern of now convergence and the septal angle throughout sys tole were observed. The velocity distribution in the aortic annulus ch anged according to the pattern of flow convergence in the left ventric ular outflow tract. During early systole, the pattern of flow converge nce was most asymmetrical. With the central longitudinal axis of the a ortic annulus as a reference, the main part of the converging flow was along the anterior wall of the left ventricular outflow tract. Conseq uently, the velocity profile in the aortic annulus was most skewed dur ing the early systole, with the highest velocity along the anterior wa ll. Towards late systole, the pattern of flow convergence became more and more symmetrical, and the velocity distribution in the aortic annu lus gradually became flat, A significant correlation was found between the extent of asymmetry of the pattern of flow convergence in the lef t ventricular outflow tract and the extent of skewness of the velocity distribution in the aortic annulus (r = 0.69, P < 0.001). Throughout systole, septal angle increased very slightly (from 35 +/- 3 to 38 +/- 3 degrees, P < 0.01). The pattern of flow convergence in the left ven tricular outflow tract is a major determinant of the velocity distribu tion in the aortic annulus in pigs.