Andersons pediatric cardiology 175

Ventriculovascular Coupling Fetal Systemic Pressures Direct measurements of intraventricular pressure have been made in the normal heart between 18 and 29 weeks of gestation.195 These studies have confirmed that ventricular systolic pressures increase with gestation In fetuses in which it was possible to record measurements in both ventricles, the pressures were equal, as expected End-diastolic pressures that have previously only been inferred from Doppler assessment were also directly measured (Fig 6.20) Speckle tracking techniques have been used to trace the endovascular border of the aorta profiled in an axial plane in the fetal chest at the level of the fourchamber view to measure the aortic fractional area change (AFAC) Animal studies have shown good correlation with blood pressure and its amplitude measured directly in a fetal lamb model.196 In the human fetus, intertwin pair differences in AFAC were reported in monochorionic pregnancies complicated by TTTS, with higher values in the recipient twin of a pair compared with its donor twin, consistent with a higher pulse pressure No intertwin pair differences were observed in uncomplicated monochorionic twin pairs Furthermore, AFAC correlated with combined cardiac output and ventricular filling pressures, thus proving its potential utility in monitoring fetal response to therapies (Fig 6.21).197 FIG 6.20 Pressure traces showing the systolic and end-diastolic measurements within the human fetal ventricle at 22 weeks of gestation for the left ventricle (A) and the right ventricle (B) (From Johnson P, Maxwell DJ, Tynan MJ, Allan LD Intracardiac pressures in the human fetus Heart 2000;84:59–63.) FIG 6.21 (A) The endovascular border of the mid-thoracic aorta in the four-chamber view was traced manually during systole with timing guided by anatomic M-mode and the aortic fractional area change averaged over three cardiac cycles (B) A sample area-time diagram from a fetus acquired