Assessment of mitral A-wave transit time to cardiac outflow tract and isovolumic relaxation time of left ventricle in the appropriate and small-for-gestational-age human fetus

Abstract

Mitral A-wave transit time (Ta; ms) from the mitral valve to the left ventricular outflow tract and left ventricular isovolumic relaxation time (IRT) were studied by pulsed Doppler ultrasound in 17 appropriate-for-gestational-age fetuses (AGA, 30–39 wk) and 12 small-for-gestational-age fetuses (SGA, 30–36 wk). Ta was measured from the peak of the A-wave to the peak of the reflected A-wave (Ar) from the left ventricular wall. IRT was determined from the interval between the aortic valve closure artefact and the onset of transmitral flow. The mean Ta in the SGA fetus (42 ± 7 [1 SD] ms) was significantly shorter ( p < 0.03) than in the AGA fetus (47 ± 11 [1 SD] ms), whereas this was not so for IRT (51 ± 8 [1 SD] ms vs. 60 ± 15 [1 SD] ms). In the SGA fetus, a positive correlation ( r = +0.82, p < 0.01) was established between Ta (ms) and gestational age. No such correlation existed for the AGA fetus. It is speculated that, in the SGA fetus, the shorter Ta may reflect an increase in left ventricular stiffness.