VELOCITY DISTRIBUTIONS IN THE LEFT-VENTRICULAR OUTFLOW TRACT IN PATIENTS WITH VALVULAR AORTIC-STENOSIS - EFFECT ON THE MEASUREMENT OF AORTIC-VALVE AREA BY USING THE CONTINUITY EQUATION

Tire cross-sectional velocity distribution in the left ventricular out flow tract was studied in 40 patients with valvular aortic stenosis. D oppler colour flow mapping and a time-interpolation method were used t o construct the cross-sectional velocity and time-velocity integral (T VI) profiles at different levels. By using pulsed Doppler, the subaort ic flow velocity was sampled from the anterior, middle and posterior r egions along the diameter of the left ventricular outflow tract (at 0. 5 to 1.0 cm proximal to the aortic anulus) in the apical long axis vie w. Thus, for each patient, three aortic valve areas were calculated by using the continuity equation. Each patient was assigned to one of th ree subgroups according to the left ventricular ejection fraction (EF) : subgroup I with EF less than or equal to 25% (n=10), subgroup II wit h 25%<EF less than or equal to 50% (n=17) and subgroup III with EF>50% (n=13). Velocity distributions in the three subgroups were compared t o each other. Results: (1) The velocity distribution in the left ventr icular outflow tract was skewed with the highest velocities and TVIs a long the anterior wall and septum. The skewness of the velocity distri bution was more pronounced in the apical long axis view than in the fo ur chamber view (P<0.05). The extent of skewness of the TVI profile wa s positively correlated to the left ventricular EF both in the long ax is view (r=0.63; P<0.001) and in the four chamber view (r=0.57; P<0.00 1). (2) Pulsed Doppler sampling from different regions along the diame ter produced different TVIs, and therefore yielded significantly diffe rent calculated aortic valve areas, especially in subgroup III. Due to the skewness of the velocity distribution in the left ventricular out flow tract, location of the pulsed Doppler sample volume significantly affects the accuracy of aortic valve area calculation by using the co ntinuity equation, especially in patients with relatively high left ve ntricular EF. In patients with low EF, selection of pulsed Doppler sam pling site is less important.