24-hour ECG frequency-domain measures in preeclamptic and healthy pregnant women during and after pregnancy

Objective: The aim of the present study was to evaluate the autonomic balance in women with preeclampsia and in healthy women during and after pregnancy by means of a 24-h ECG Holter recording combined with power spectral analysis. Methods: Fifteen preeclamptic and 15 healthy women underwent 24-h Holter monitoring in the 32nd-36th week of gestation and 3-6 months postpartum. The power spectrum of the maternal electrocardiogram was analyzed with an autoregressive algorithm. Main Outcome Measures: The power spectrum contains two major components: a low-frequency peak, primarily attributed to sympathetic tone, and a high-frequency peak, reflecting vagal tone. Results: The power spectrum of maternal heart rate variability did not differ between preeclamptic and normal women during pregnancy. After delivery, the amplitude of all components became significantly higher than those during pregnancy, with one exception: the high-frequency component in the patients who had been preeclamptic. In a comparison of the two groups, the high-frequency component after delivery was significantly lower in women who had preeclampsia than in normal healthy women (p = 0.03). Conclusions: During pregnancy, the power spectrum is reduced and cannot be used to distinguish between patients with preeclampsia and normal healthy women. Three to 6 months after delivery, the high-frequency component is still reduced in the preeclamptic group of women. This indicates an impaired vagal modulation even in the nonpregnant state in this group of women, unlike those who had a normotensive pregnancy.