Arterial haemodynamics and blood gas status are largely preserved in fetal sheep with chronically increased left ventricular afterload

  • Mr Andrew Hattam, Heart Research Group, Murdoch Children's Research Institute, Australia
  • Mr Magdy Sourial, The Royal Children's Hopsital, Australia
  • Dr Paul Brooks, Heart Research Group, Murdoch Children’s Research Institute, Australia
  • Prof Daniel Penny, The Royal Children's Hopsital, Melbourne, Australia
  • A/Prof Joseph Smolich, Heart Research Group, Murdoch Children’s Research Institute, Australia

    • Objective: Although recent studies from our laboratory suggest that chronically increased left ventricular (LV) afterload in the fetus is associated with LV remodelling, the effect of such remodelling on haemodynamics and arterial blood gas status is unknown. We addressed this question in near-term fetal sheep with chronically increased LV afterload imposed at mid-gestation.

    Methods: In twelve twin pregnancies, one fetus underwent non-constrictive ascending aortic banding under anaesthesia at 92±3 days gestation (term=147 days), with the other fetus serving as a control. After near-term (140±1 days) anaesthesia of the ewe, both fetuses underwent echocardiography followed by insertion of axillary arterial (Ax), pulmonary arterial (PA) and left atrial (LA) fluid-filled catheters, and in a subgroup (n=6), an apical LV micromanometer catheter.

    Results: An ascending aortic pressure gradient of 26±13 mmHg was present on echocardiography in banded fetuses, without evidence of cardiac failure. Mean Ax (48±6 vs 52±7 mmHg) and PA pressures (49±6 vs 53±7 mmHg) were similar in control and banded fetuses. However, in banded fetuses, mean LA pressure (6±2 vs 4±2mmHg, p<0.05) and LV end-diastolic pressure (11±3 vs 8±2 mmHg, p<0.05) were lower, while the maximal rate of rise of LV pressure was higher (1401±279 vs 1950±480 mmHg/s, p<0.05). Apart from a lower pH (7.273±0.052 vs 7.215±0.093; p<0.05) and higher PCO2 (51.3±5.5 vs 57.5±7.8 mmHg; p<0.05) in banded fetuses, Ax blood gas variables were not different between groups.

    Conclusion: Arterial blood pressures are maintained and blood gas status is largely unimpaired in fetal sheep with chronically increased LV afterload.