Effects of tocolytic treatment with ritodrine on cardiovascular autonomic regulation

Abstract

Objective: To study the acute effects of tocolytic treatment with intravenous ritodrine on cardiovascular autonomic regulation.

Design: Validated methods to assess cardiovascular autonomic nervous function-heart rate and blood pressure variability and vagal cardiac baroreflex sensitivity-were measured before and during ritodrine infusion.

Setting: Turku University Central Hospital, Turku, Finland.

Sample: Twelve pregnant women admitted to hospital for threatened preterm labour.

Methods: Electrocardiogram and continuous noninvasive finger blood pressure signals were recorded in each woman, resting in a supine position. Autoregressive spectrum analysis was used to quantify short term heart rate and blood pressure variability. Vagal cardiac baroreflex sensitivity was measured as the bradycardia response to an intravenous bolus injection of phenylephrine.

Main outcome measures: Vagal cardiac baroreflex sensitivity and spectrum analysis indices of short term heart rate and blood pressure variability.

Results: Ritodrine significantly decreased vagal cardiac baroreflex sensitivity as well as total (0.00-0.40 Hz), low frequency (0.04-0.15 Hz) and high frequency (0.15-0.40 Hz) power bands of the heart rate variability spectrum. Ritodrine significantly increased mean heart rate and the low frequency power band of the systolic blood pressure variability spectrum.

Conclusions: In pregnant women with threatened preterm labour intravenous administration of ritodrine decreases vagal cardiac baroreflex sensitivity and vagal modulation of heart rate, and increases sympathetically mediated blood pressure variability. Decreased baroreflex sensitivity and heart rate variability are known to be associated with a poor prognosis in some patient groups, so the effects of ritodrine tocolysis may be unfavourable in women with impaired circulatory homeostasis.