Effects of tocolytic treatment with ritodrine on cardiovascular autonomic regulation

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 and as total (0.00-0.40 Hz), low frequency (0.04-0.15 Hz) and high frequency (0.15-0.04 Hz) power bands of the heart rate variability spectrum. Ritodrine significantly increased mean heart rate and the low frequency quency 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.