Tachysystole
Abstract & Commentary
By John C. Hobbins, MD, Professor of Obstetrics and Gynecology, University of Colorado Anschutz Medical Campus, Aurora, CO, is Associate Editor for OB/GYN Clinical Alert.
Dr. Hobbins reports no financial relationships relevant to this field of study.
Synopsis: A recent study has shown that tachysystole by ACOG definition occurs at least once in almost 50% of misoprostol inductions; however, this did not have an adverse effect on neonatal well-being despite an increase in cesarean section rate.
Source: Stewart RD, et al. Defining uterine tachysystole: How much is too much? Am J Obstet Gynecol 2012;207:290.e1-6.
There has been a steady rise of labor inductions in the United States during the last decade, a trend that has gone hand-in-hand with the cesarean section rate. At last count, at least one in five deliveries results from inductions of labor. Although the decision to induce can involve a complicated process applied to many different clinical situations, the word “elective” remains a common indication. Once induction has been initiated, rarely is there any turning back. In fact, it is not unusual for too many contractions to occur over a short time period in the early stages of induction — often leading to immediate intervention. Using the American College of Obstetricians and Gynecologists definition of tachysystole as “more than six contractions in a 10-minute period” a group from Parkland Hospital in Dallas set out to see if tachysystole had any significant impact on neonatal outcome.
Stewart et al reviewed fetal heart rate monitoring data over 18 months in 453 laboring women who had had misoprostol (prostaglandin E1) inductions. Uterine activity was analyzed by assessing the maximum number of contractions per 10 minutes, averaged over a 30-minute period. The neonatal outcomes consisted of 5-minute Apgar scores of ≤ 3, an umbilical artery pH of < 7.1, neonatal seizures, admission to the newborn special care unit, and perinatal death. These variables were also lumped together as a “fetal vulnerability composite.”
Of the patients in this study, 253 (43%) had at least one episode where six or more contractions occurred over a 10-minute period. However, when averaged over a 30-minute window, 220 had “sustained tachysystole” (> 14 contractions). Neither the fetal vulnerability composite nor the individual categories of adverse outcome correlated with the amount of contractions over any 30-minute period. Interestingly, the degree of the tachysystole that had the greatest association with fetal heart rate decelerations was at 17 to 19 contractions over a 30-minute period.
At least one episode of hypertonus (which was not defined in the study methods) occurred in 15% of patients. Although this did not have an overt effect on the fetal vulnerability composite, it did have an effect on the incidence of fetal heart rate decelerations, and, not surprisingly, was associated with an increase in the cesarean section rate.
Commentary
This study provides mixed messages. Inductions can result in tachysystole and this, in turn, can result in worrisome fetal heart rate changes and, perhaps, unnecessary cesarean sections. However, episodes of tachysystole are common and do not seem to have an effect on short-term neonatal outcome.
In summary, induction of labor cannot be painted as an innocuous strategy, since the rather common tachysystole can have a temporary effect on the fetal heart rate — our measure of fetal well-being. Therefore, there should be a good reason to preempt a natural process. However, on the bright side, the study suggests that even when the uterus over-responds to this type of induction, a little patience will generally result in the vaginal delivery of a baby who seemingly can be quite tolerant to the process.
There has been a steady rise of labor inductions in the United States during the last decade, a trend that has gone hand-in-hand with the cesarean section rate.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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