Chronically elevated left ventricular afterload in fetal sheep prevents gestational increase in isovolumic acceleration

  • Dr Paul Brooks, The Royal Children's Hopsital, Murdoch Children's Research Institute, University of Melbourne, Australia
  • Mr Andrew Hattam, Murdoch Children's Research Institute, Department of Paediatrics University of Melbourne, Australia
  • Dr Michael Cheung, The Royal Children's Hopsital, Murdoch Children's Research Institute, University of Melbourne, Australia
  • Prof Daniel Penny, The Royal Children's Hopsital, Murdoch Children's Research Institute, University of Melbourne, Australia
  • A/Prof Joseph Smolich, Murdoch Children's Research Institute, Department of Paediatrics University of Melbourne

    • Aims: Fetal ventricular contractility is generally assessed by echocardiographic indices whose acute load dependence is well recognized. Color tissue Doppler (cTDI) isovolumic acceleration (IVA), an index of contractility relatively insensitive to acute changes in loading conditions, may permit more accurate evaluation of fetal systolic function. However, the impact of chronic loading changes on cTDI indices in the fetus is unknown. This study assessed the effect of chronically elevated left ventricular (LV) afterload on systolic cTDI indices in fetal sheep.

    Methods: In 17 twin ovine pregnancies, one fetus had a surgical non-constrictive ascending aortic band placed at a median 91 days gestation (range 90-98 days, term=147 days), whilst the other served as an un-operated control. Echocardiograms of both fetuses were performed under maternal sedation at ~2 weekly intervals until near term. Left and right ventricular (RV) IVA and peak systolic (S’) velocities were obtained at their respective atrioventricular valve annulus. Ventricular outputs and peak ascending aortic gradient were obtained with standard Doppler techniques.

    Results: Gestation related increases in LV and RV outputs did not differ in banded and control groups despite a moderate peak ascending aortic gradient in near-term banded fetuses (23.9±11.5mmHg). LV and RV S’ and RV IVA showed no differences between banded and control groups. However, the gestation related increase in LV IVA present in control fetuses was absent in banded animals (p=0.004)

    Conclusions: These results suggest a significant impact of chronically elevated afterload on IVA in the fetus, the mechanism of which requires clarification with invasive studies.