Contribution of Velocity Profiles at the Left Ventricular Outflow Tract to Calculations of Stroke Volume

OBJECTIVE: The goal of the study was to determine whether the central velocity of the left ventricular outflow tract represents the mean velocity of the total outflow area. METHODS: Thirteen healthy men (mean age, 30 +/- 6 years) and nine patients with aortic valve disease (seven with aortic regurgitation and two with aortic valve stenosis) were examined. Cine gradient echo images were obtained in the left ventricular outflow long axis. Cine images with velocity mapping were obtained in the short axis of the outflow tract. Values for peak velocity were obtained on the right-left axis and on the anteroposterior axis. Distances were measured along the axes from the right and anterior edges of the outflow tract at the point of peak velocity. Percentages of the distances for outflow diameter were calculated. Peak velocity at the left ventricular outflow tract using pulsed-Doppler method were also measured. RESULTS: In normal subjects and in patients, on the right-left axis, the peak velocity was 87 +/- 16 and 72 +/- 11 cm/sec, respectively, and the distance from the right edge of outflow tract corresponded to 19% +/- 8% and 21% +/- 7%, respectively. On the anteroposterior axis, the peak velocity was 86 +/- 16 and 60 +/- 9 cm/sec, and the corresponding distance from the anterior edge was 30% +/- 13% and 41% +/- 12% for normal subjects and patients, respectively. The central velocity of the outflow tract was 74 +/- 15 cm/sec, whereas the mean of the total outflow tract was 74 +/- 13 cm/sec. Central and mean velocities of the outflow tracts as revealed by magnetic resonance imaging showed a close and highly significant correlation in both groups. Velocity obtained by pulsed-Doppler method and mean velocity of the outflow tract by magnetic resonance imaging also showed significant correlation in both groups. CONCLUSIONS: Central velocity at the left ventricular outflow tract represented the mean of the total outflow tract both in normal subjects and in patients with aortic valve disease. The stroke volume measured by pulsed Doppler is therefore considered reliable if the sampling point is placed exactly at the center of the outflow.