Effects of activity on ascending aortic velocity in children with valvar aortic stenosis

Abstract

The peak velocity of aortic blood flow was measured in 12 normal children and 20 children with valvar aortic stenosis (AS) by continuous-wave Doppler ultrasound (CWD). Measurements were made at rest, after 2 forms of exercise and, in the 11 children who underwent cardiac catheterization, while under sedation. The exercise was both formal cycle ergometry and a 200-meter jog. The peak velocity in normal children was 1.5 ± 0.2 m/s at rest, increasing to 2.1 ± 0.4 m/s (p < 0.01) after running and to 1.9 ± 0.4 m/s (p < 0.01) after cycling. Peak velocity in children with AS was 3.5 ± 0.8 m/s at rest, increasing to 4.4 ± 0.8 m/s (p < 0.01) after running and to 4.5 ± 0.5 m/s (p < 0.01) after cycling. The increase in peak velocity was greater in children with AS than in normal children. Measurements of left ventricular (LV) aortic pressure differences by cardiac catheterization were compared to those made by CWD, using the modified Bernoulli equation. The best correlation of the CWD prediction of LV aortic pressure differences was achieved when the children were sedated. The peak velocity of blood flow in the ascending aorta varied with level of activity, and this variability must be considered when using the Bernoulli equation to predict LV aortic pressure differences. CWD prediction of the LV aortic pressure difference was best when the child was sedated (r = 0.98). It is therefore prudent to consider the velocity measurement proximal to the AS to calculate LV aortic pressure differences more accurately unless the child is sedated. Peak velocity of blood flow may be measured in the ascending aorta after termination of exercise. Measurements made after limited exercise may predict the level of increase in peak velocity that occur after more formal testing.