Understanding Fetal Heart Rate Patterns That May Predict Antenatal and Intrapartum Neural Injury

Electronic fetal heart rate (FHR) monitoring is widely used to assess fetal well-being throughout pregnancy and labor. Both antenatal and intrapartum FHR monitoring are associated with a high negative predictive value and a very poor positive predictive value. This in part reflects the physiological resilience of the healthy fetus and the remarkable effectiveness of fetal adaptations to even severe challenges. In this way, the majority of "abnormal" FHR patterns in fact reflect a fetus' appropriate adaptive responses to adverse in utero conditions. Understanding the physiology of these adaptations, how they are reflected in the FHR trace and in what conditions they can fail is therefore critical to appreciating both the potential uses and limitations of electronic FHR monitoring.

The change of fetal heart rate short-term variability during the course of histological chorioamnionitis in fetal sheep

OBJECTIVE

Histological chorioamnionitis (CAM) is related to neonatal mortality and morbidity. However, identifying intrauterine inflammation before delivery is challenging. The aim of this study was to investigate the changes in fetal heart rate (FHR) short-term variability (STV) during the course of histological CAM.

STUDY DESIGN

Changes in STV were measured in 7 chronically instrumented fetal sheep at 111-120 days of gestation. Lipopolysaccharide (LPS) was infused into the amniotic cavity for 2 days following the 4th postoperative day to develop histological CAM. STV was determined based on the R to R interval of the fetal electrocardiogram. We continued to observe the changes in STV until the time of intrauterine fetal death (IUFD). The umbilical cord and fetal membranes were evaluated histologically after IUFD. The experiment was divided into two phases: 1) the acute phase, defined as the 24-hour period between the first and second injections of LPS and 2) the perimortem phase, defined as the period between the second injection of LPS and IUFD. Changes in STV in both the acute and perimortem phases were evaluated using Friedman's test. A probability of <0.05 was accepted as statistically significant.

RESULTS

The fetuses died, on average, at 23.7 ± 4.9 h after the second injection of LPS. Both the umbilical cord and fetal membranes showed histological evidence of severe inflammation. During the perimortem phase, there were statistically significant differences in STV at each time point. STV increased significantly at 6, 4, and 3 h before intrauterine fetal death compared to the baseline.

CONCLUSION

Our study suggests that STV increased as the fetal condition deteriorated during the course of histological CAM.

Accuracy of signs of clinical chorioamnionitis in the term parturient

OBJECTIVE

Uniform histopathologic guidelines were applied to diagnose chorioamnionitis and estimate the accuracy of clinical signs in term parturients.

STUDY DESIGN

A retrospective cohort study utilized slides from term parturient placentas with Amniotic Fluid Infection Nosology Committee guidelines as the gold standard. Sensitivity, specificity and accuracy for fever, maternal tachycardia and fetal tachycardia were calculated.

RESULT

Of 641 placentas, 367 (57.3%) had histologic chorioamnionitis and 274 (42.7%) were negative. Fever had a sensitivity of 42%, specificity of 86.5% and accuracy of 61%. Fever, maternal tachycardia and fetal tachycardia had a sensitivity of 18.3%, specificity of 98.2% and accuracy of 52.4%.

CONCLUSION

Histologic chorioamnionitis, frequently asymptomatic, is a common finding in placentas examined from term parturients. Clinical signs are not accurate in the diagnosis. Adoption of uniform pathologic guidelines will facilitate research into the clinical significance of these lesions in the future.

The association of histologic placental inflammation with category II fetal heart tracings

The present study assessed whether placentas in women delivered by cesarean for category II fetal heart tracings (FHT) exhibit a higher incidence of acute inflammation than those of women delivered by cesarean for labor arrest. This case control study included singleton pregnancies ≥36 weeks of gestation delivered by cesarean for an FHT indication (cases) or because of labor arrest (controls) 2005-2009 at Prentice Women's Hospital. Exclusions were maternal diabetes, hypertension, known thrombophilia, connective tissue disorders, clinical evidence of chorioamnionitis, placental abruption, fetal anomalies, stillbirth, or an infant with a birth weight less than the 10th percentile. Women were included in the case group if the indication for cesarean delivery was based on the FHT and review of the FHT determined that they were designated as category II prior to delivery. A perinatal pathologist, unaware of indications for delivery, assessed placental inflammation in maternal and fetal compartments. Stage and grade of acute inflammation, from none to severe (scored 0-3), in the membranes, chorionic plate, chorionic vessels, and umbilical cord were assessed, and overall maternal and fetal inflammatory stages were assigned. Findings indicative of chronic inflammation were also noted. Other than lower umbilical artery cord gases in women with category II FHT, cases (n  =  51) and controls (n  =  27) had similar baseline characteristics and newborn outcomes, as well as similar placental pathologic findings. In uncomplicated patients, the presence or extent of placental inflammation does not appear to differ between women delivered for category II FHT and labor arrest.

Cytokine screening identifies NICU patients with Gram-negative bacteremia

INTRODUCTION

Biomarkers and physiomarkers may be useful adjunct tests for sepsis detection in neonatal intensive care unit (NICU) patients. We studied whether measuring plasma cytokines at the time of suspected sepsis could identify patients with bacteremia in centers in which patients were undergoing continuous physiomarker screening using a heart rate characteristics (HRC) index monitor.

RESULTS

Six cytokines were higher in Gram-negative bacteremia (GNB) than in Gram-positive bacteremia or candidemia (GPBC). A cytokine score using thresholds for granulocyte colony-stimulating factor (G-CSF), interleukin (IL)-6, IL-8, and tumor necrosis factor (TNF)-α had 100% sensitivity and 69% positive predictive value (PPV) for GNB. A single cytokine marker, IL-6 < 130 pg/ml, had 100% sensitivity and 52% PPV for sepsis ruled out (SRO). The average HRC index was abnormal in this cohort of patients with clinical suspicion of sepsis and did not discriminate between the final sepsis designations.

DISCUSSION

In summary, in NICU patients with suspected late-onset sepsis, plasma cytokines can identify those with SRO and those with GNB, potentially aiding in decisions regarding therapy.

METHODS

Seven cytokines were measured in 226 plasma samples from patients >3 d old with sepsis suspected based on clinical signs, abnormal HRC index, or both. Cases were classified as SRO, clinical sepsis (CS), GPBC, or GNB.

Pathogen-induced heart rate changes associated with cholinergic nervous system activation

The autonomic nervous system plays a central role in regulation of host defense and in physiological responses to sepsis, including changes in heart rate and heart rate variability. The cholinergic anti-inflammatory response, whereby infection triggers vagal efferent signals that dampen production of proinflammatory cytokines, would be predicted to result in increased vagal signaling to the heart and increased heart rate variability. In fact, decreased heart rate variability is widely described in humans with sepsis. Our studies elucidate this apparent paradox by showing that mice injected with pathogens demonstrate transient bradyarrhythmias of vagal origin in a background of decreased heart rate variability (HRV). Intraperitoneal injection of a large inoculum of Gram-positive or Gram-negative bacteria or Candida albicans rapidly induced bradyarrhythmias of sinus and AV nodal block, characteristic of cardiac vagal firing and dramatically increased short-term HRV. These pathogen-induced bradycardias were immediately terminated by atropine, an antagonist of muscarinic cholinergic receptors, demonstrating the role of vagal efferent signaling in this response. Vagal afferent signaling following pathogen injection was demonstrated by intense nuclear c-Fos activity in neurons of the vagal sensory ganglia and brain stem. Surprisingly, pathogen-induced bradycardia demonstrated rapid and prolonged desensitization and did not recur on repeat injection of the same organism 3 h or 3 days after the initial exposure. After recovery from the initial bradycardia, depressed heart rate variability developed in some mice and was correlated with elevated plasma cytokine levels and mortality. Our findings of decreased HRV and transient heart rate decelerations in infected mice are similar to heart rate changes described by our group in preterm neonates with sepsis. Pathogen sensing and signaling via the vagus nerve, and the desensitization of this response, may account for periods of both increased and decreased heart rate variability in sepsis.