Myocardial ischemia: a complication of ritodrine tocolysis

Increased Subsequent Risk of Coronary Heart Disease in Primary Cesarean Delivery Women: A Population-Based Cohort Study

BACKGROUND

Impacts of delivery modes on the subsequent risk of coronary heart disease (CHD) in pregnant women have not been elucidated.

MATERIALS AND METHODS

Data of women who had undergone cesarean delivery (CD cohort) or vaginal delivery (VD cohort) between January 2000 and December 2012 from Taiwan Health Insurance Database were analyzed. All subjects were tracked until December 31, 2013. For women with multiple deliveries, only the first delivery data were included. Study end point was the diagnosis of new-onset CHD after delivery.

RESULTS

In total, 51,765 subjects (CD cohort: n = 17,839; VD cohort: n = 33,926) were included. During 1-14 years of follow-up, the incidence rate of new-onset CHD in the CD cohort was significantly higher than in the VD cohort (1.3% [231/17,839] vs. 0.8% [257/33,926], p < 0.001; effect size: 0.30). Analysis revealed that the subsequent risk of CHD in the CD cohort was significantly higher than in the VD cohort (adjusted hazard ratio [HR] = 1.28, 95% confidence intervals [CI]: 1.06-1.55, p = 0.012). We performed sensitivity tests by excluding subjects who had undergone CD due to nonmedical reasons from the CD cohort. The remaining subjects were named as the *CD cohort. Analysis also revealed a higher subsequent risk of CHD in the *CD cohort than in the VD cohort (adjusted HR = 1.32, 95% CI: 1.08-1.60, p = 0.006).

CONCLUSIONS

Women who had undergone primary CD, especially those who had undergone CD due to medical reasons, were associated with an ∼30% higher risk of CHD than those who had undergone VD.

Risk-benefit effects of tocolytic therapy

Tocolytics are potent drugs that are used to interdict preterm labour. Although all of these agents have some side effects, if not frankly adverse effects under certain clinical situations, two of these drugs, the beta-mimetics and magnesium sulphate (MgSO(4)), have been found to have considerable potential for adverse maternal cardiovascular and respiratory effects. Furthermore, magnesium sulphate has been shown to have harmful, indeed, sometimes lethal, effects in some babies. Although less well established, NSAIDs, the most common example of which is indomethacin, also have some important adverse effects in fetuses. Within the limits of contemporary scientific knowledge, calcium channel blockers, such as nifedipine, appear to be among the more efficacious and safer drugs that are currently being used for tocolysis.

Pharmacokinetics of Tocolytic Agents

Tocolytic agents are drugs designed to inhibit contractions of myometrial smooth muscle cells. Such an effect has been demonstrated in vitro or in vivo for several pharmacological agents, including beta-adrenergic agonists, calcium channel antagonists, oxytocin antagonists, NSAIDs and magnesium sulfate. However, the aim of tocolysis is not only to stop uterine contractions or to prevent preterm delivery, but to prevent perinatal morbidity and mortality associated with preterm birth. The achievement of this goal has not yet been clearly demonstrated for any of the drugs available, and the use of tocolytic agents may appear controversial. Therefore, it is important to avoid maternal and fetal toxicity when tocolytic agents are used. During pregnancy, all steps of drug pharmacokinetics are altered. Absorption of drugs administered orally is limited because of delayed stomach emptying and reduced intestinal motility. The volume of distribution of drugs is increased. The metabolic activity of the liver is increased, accelerating the metabolism of lipophilic drugs. Renal filtration is increased, leading to enhanced renal elimination of water-soluble drugs. These modifications are generally responsible for reduced plasma concentration and reduced half-life of most drugs. These specific modifications have to be taken into account when using a drug in pregnant women. The aim of this review is to provide the reader with pharmacological data about drugs currently used to treat preterm labour. Such data in pregnant women may affect the choice of optimal drug dosage and route of administration.

Adverse and beneficial effects of tocolytic therapy

In addition to questions raised about the efficacy of many tocolytics, appropriate concern has been voiced about the safety of these potent drugs. Although some degree of risk for adverse effects with drugs promising a strong therapeutic effect can be accepted, caution needs to be exercised when benefits are marginal or unproven. Unfortunately, some of the tocolytics, most notably the betamimetics and magnesium sulfate, have been found to have considerable potential for adverse maternal cardiovascular and respiratory effects. Although less clearly established, the use of indomethacin appears to be associated with increased fetal and neonatal risks. Concerning magnesium sulfate, in addition to the well-known maternal effects, the accumulating evidence showing an increased frequency of adverse outcomes in the fetus and neonate has led to the recommendations to abandon its use entirely as a tocolytic. Given the limitations of our current state of knowledge, nifedipine would appear to be among the more efficacious and safer tocolytics available to use when properly indicated.

Randomized trial of oral indomethacin and terbutaline sulfate for the long-term suppression of preterm labor

OBJECTIVE

Our purpose was to determine the efficacy and safety of long-term oral tocolysis with indomethacin or terbutaline sulfate.

STUDY DESIGN

Seventy-one patients at 26 to 32 weeks' gestation admitted for preterm labor were prospectively randomized to receive oral indomethacin or terbutaline sulfate after successful intravenous tocolysis. Patients were monitored weekly for cervical change, maternal side effects, amniotic fluid volume, and constriction of the fetal ductus arteriosus. Patients receiving indomethacin were converted to terbutaline at 34 weeks or with the occurrence of fetal ductal constriction or oligohydramnios.

RESULTS

Of 71 patients randomized six were excluded after randomization. Thirty-three patients were randomized to indomethacin and thirty-two to terbutaline. There were no differences in the percentage of patients achieving 34 weeks of gestation. No differences in neonatal outcome were noted. Nine (27%) fetuses receiving indomethacin had constriction of the fetal ductus arteriosus, and 13 (38%) had oligohydramnios. Most patients on terbutaline reported beta-mimetic side effects (53%), but only one required discontinuation of therapy.

CONCLUSION

Both indomethacin and terbutaline sulfate are effective tocolytics, but major fetal side effects are common with long-term indomethacin use.

Role of the baroreflex in beta 2-sympathomimetic induced tachycardia in male rats

The aim of the study was to determine whether tachycardia which is associated with the use of beta 2-sympathomimetic tocolytic agents is caused by baroreflex activation or by direct stimulation of cardiac beta-adrenoceptors. In conscious male rats, tachycardiac responses following intravenous injection of hexoprenaline, ritodrine and fenoterol were compared following (i) bilateral sinoaortic denervation (SAD) or (ii) sham-operation, and (iii) ganglionic-blockade using hexamethonium. Dose-ranges were chosen to result in similar reductions in diastolic blood pressure (DAP). Furthermore, following ganglionic blockade, the relative contribution of beta 1-adrenoceptor stimulation was assessed using the selective beta 2-receptor antagonist ICI 118,551. In intact rats, increases in HR induced by all beta-adrenoceptor agonist were comparable. In SAD and ganglion-blocked rats, DAP fell more pronounced at even lower doses. The corresponding increases in HR were approximately 3 times smaller than in intact rats but not different between agents. During ganglionic blockade ICI 118,551 significantly inhibited HR responses to fenoterol and hexoprenaline but not ritodrine. The conclusion is that in intact male rats, baroreflex activation is the major determinant of tachycardia following injection of ritodrine, fenoterol or hexoprenaline. Increasing the beta 2-selectivity of these drugs will not limit the tachycardic effects.

Effects of terbutaline sulfate on fetal cardiac function

An isolated heart preparation was used to study the effects of terbutaline sulfate (Brethine) on fetal cardiac function. Pregnant guinea pigs received daily subcutaneous injections of terbutaline for 10 day, whereas a control group received placebo injections. Fetal guinea pig hearts were evaluated for cariodynamic and pathologic differences. Fetuses exposed to terbutaline demonstrated a higher mean heart rate (p less than 0.01), a higher mean heart weight (p less than 0.05), a higher mean heart weight/body weight ratio (p less than 0.01), and a trend toward higher left ventricular systolic pressure levels (p less than 0.1). These hemodynamic responses in fetuses exposed to terbutaline may result in increased functional demands that may predispose myocardial tissue to damage.

Cardiac isoenzymes and electrocardiographic changes during ritodrine tocolysis

To investigate the potential myocardial ischemic effects of ritodrine, we studied 36 singleton and four twin preterm pregnancies during ritodrine therapy. We serially determined serum creatinine phosphokinase (CPK-MB fraction) and lactic dehydrogenase isoenzymes and performed electrocardiography before and during ritodrine infusion and again within the first 24 hours of oral drug therapy. We observed that serum CPK-MB and lactic dehydrogenase isoenzymes remained within the normal range during therapy periods. The incidence of sinus tachycardia and non-specific T wave changes were 100% and 25%, respectively. In three of four twin pregnancies, ST-T segment depression in leads I, V4, V5, and V6 of the electrocardiogram was noted. Our study suggests that (1) the recommended ritodrine regimen does not produce direct myocardial damage, and (2) ritodrine may cause cardiac ischemia as determined by electrocardiography, which theoretically would progress to myocardial damage if not treated properly.

Terbutaline (intravenous bolus) for the treatment of acute intrapartum fetal distress

beta 2-Sympathomimetics have been used in acute intrapartum fetal distress to abolish uterine contractions and thus enable the fetal metabolism to recover before delivery. Because some serious complications were reported when a terbutaline intravenous bolus (0.25 mg) was used as a tocolytic, we assessed its safety and efficacy when used in patients not affected by cardiovascular disease, tachycardia greater than 100 beats/min, thyrotoxicosis, fluid overload, corticoids, atropine, or severe abruptio placentae. No maternal or fetal complications occurred in the 36 patients studied; a well-tolerated tachycardia developed in most patients. Fetal heart rate tracings and pH improved in 32 patients. Thirty-four neonates were delivered in good clinical and metabolic condition. We conclude that terbutaline intravenous bolus 0.25 mg is a safe and efficacious procedure when the proper indications and contraindications are followed.

Indomethacin in the treatment of premature labor. Effects on the fetal ductus arteriosus

Indomethacin is a potent agent in the treatment of premature labor, but its use has been limited because of concern about its constrictive effects on the fetal ductus arteriosus. To study these effects we used serial fetal echocardiography in 13 pregnant women in premature labor who received indomethacin according to three different dose schedules, ranging from 100 to 175 mg per day, for a maximum of 72 hours. The gestational ages of the fetuses ranged from 26.5 to 31.0 weeks. The detection of ductal constriction in 7 of the 14 fetuses by echocardiography led to the discontinuation of indomethacin. Three fetuses also had tricuspid regurgitation. There was no statistically significant difference between the mean (+/- SEM) gestational age of the fetuses with ductal constriction and that of those without constriction (29.3 +/- 0.59 and 28.4 +/- 0.52, respectively). There was no relation between serum indomethacin levels in the mothers and ductal constriction. In all seven fetuses affected, ductal constriction had resolved by the time they were restudied 24 hours after the discontinuation of indomethacin. Persistent fetal circulation was not detected in any of the 11 neonates studied after delivery. Indomethacin used to treat premature labor appears to cause transient constriction of the ductus arteriosus in some fetuses, even after short-term use.

Electrocardiographic changes associated with ritodrine-induced maternal tachycardia and hypokalemia

One hundred twelve patients in preterm labor were followed prospectively, with electrocardiograms taken before ritodrine therapy and at 6 and 24 hours of treatment. Ninety-six percent of patients developed sinus tachycardia. Other changes were seen in 79% of the study group. These changes included ST segment depression in 70%, T wave flattening or inversion in 55%, and prolongation of the QT interval in 35% of our sample. None of the electrocardiograms showed the presence of a significant axis deviation, a change in QRS interval, or arrhythmia. No correlation was seen between symptoms of ischemia and electrocardiographic changes. A drop in potassium concentration was noted initially, but a direct correlation between potassium concentrations and frequency of electrocardiographic changes was not present. We conclude that the electrocardiographic changes that are often observed during myocardial ischemia may be frequent in asymptomatic patients treated with ritodrine and that these changes may be a physiologic expression of ritodrine-induced tachycardia or hypokalemia. The validity of the use of the presence of electrocardiographic changes as the only criterion for discontinuation of ritodrine therapy is questioned.

Complications of beta-mimetic therapy in preterm labour

Selective beta-mimetic drugs are the most frequently used agents for arresting preterm labour. For this purpose these drugs have to be given in high doses for several hours and since they act on several organ systems, side-effects, some of which are potentially dangerous, appear. These hazards, which involve chiefly the cardiovascular and metabolic areas, have been examined in the light of available experience with these drugs. This review considers the possible mechanisms for the side-effects and offers suggestions on how the dangers in the use of beta-mimetic drugs in preterm labour might be avoided.