Left ventricular isovolumic relaxation and renin-angiotensin system in the growth restricted fetus

Objective: To determine left ventricular isovolumic relaxation time (LV IRT) in normally developing and growth restricted fetuses (FGR) as an indicator of fetal cardiac afterload and neonatal systolic blood pressure. Study design: A prospective longitudinal study in 124 normally developing and 47 growth restricted fetuses (FGR). LV IRT, fetal heart rate (FHR) and umbilical artery pulsatility index (PI) were determined at 2-3 week intervals starting at 22-26 weeks of gestation until delivery. Renin and angiotensin I levels were measured by radioimmunoassay in umbilical venous blood after delivery. Systolic blood pressure was measured at day 1 and day 5 of postnatal life. To evaluate the association between LV IRT, gestational age and FHR, bivariate regression analyses were performed. Results: Mean LV IRT (62 ± 8 ms) was 29 percent longer in FGR as compared to the normal subset (47 ± 6 ms) at all gestational ages (p < 0.001). Mean postnatal active plasma renin level (7.78 ± S.D. 1.03 ng/ml) and postnatal angiotensin I level (4.21 ± 0.70 ng/ml) in the FGR subset were significantly higher (p < 0.001) than in the normal subset (4.81 ± 1.04 ng/ml, renin and 2.69 ± 0.44 ng/ml, angiotensin I). There was a significant difference (p < 0.01) in systolic blood pressure between the two subsets on postnatal day 1 (FGR 52 ± 6 mmHg vs. normal 46 ± 4 mmHg) and day 5 (FGR 76 ± 5 mmHg vs. normal 60 ± 6 mmHg). Conclusion: Left ventricular isovolumic relaxation time may act as a sensitive index of increased arterial afterload in the growth retarded fetus and may herald raised systolic blood pressure in the early neonatal period.

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