Normalized spectral power of fetal heart rate variability is associated with fetal scalp blood pH

Background

Spectral power of fetal heart rate variability is related to fetal condition. Previous studies found an increased normalized low frequency power in case of severe fetal acidosis.

Aims

To analyze whether absolute or normalized low or high frequency power of fetal heart rate variability is associated with fetal scalp blood pH.

Study design

Prospective cohort study, performed in an obstetric unit of a tertiary care teaching hospital.

Subjects

Consecutive singleton term fetuses in cephalic presentation that underwent one or more scalp blood samples, monitored during labour using ST-analysis of the fetal electrocardiogram. Ten-minute continuous beat-to-beat fetal heart rate segments, preceding the scalp blood measurement were used.

Outcome measures

Absolute and normalized spectral power in the low frequency band (0.04-0.15 Hz) and in the high frequency band (0.4-1.5 Hz).

Results

In total 39 fetal blood samples from 30 patients were studied. We found that normalized low frequency and normalized high frequency power of fetal heart rate variability is associated with fetal scalp blood pH. The estimated ß of normalized low frequency power was −0.37 (95% confidence interval −0.68 to −0.06) and the relative risk was 0.69 (95% confidence interval 0.51-0.94). The estimated ß of normalized high frequency power was 0.33 (95% confidence interval 0.01-0.65) and the relative risk was 1.39 (95% confidence interval 1.01-1.92).

Conclusions

Normalized low and normalized high frequency power of fetal heart rate variability is associated with fetal scalp blood pH.     

Specific change in spectral power of fetal heart rate variability related to fetal acidemia during labor: comparison between preterm and term fetuses

Background

Spectral analysis of fetal heart rate (FHR) variability is a useful method to assess fetal condition. There have been several studies involving the change in spectral power related to fetal acidemia, but the results have been inconsistent.

Aims

To determine the change in spectral power related to fetal umbilical arterial pH at birth, dividing cases into preterm (31–36 weeks) and term (≥ 37 weeks) gestations.

Study design

Case–control study. The 514 cases of deliveries were divided into a low-pH group (an umbilical arterial pH < 7.2) and a control group (pH ≥ 7.2).

Subjects

FHR recorded on cardiotocography during the last 2 h of labor.

Outcome measures

The spectral powers in various bands of FHR variability.

Results

In preterm fetuses, the total, low (LF), and movement (MF) frequency spectral powers and LF/HF ratio were significantly lower in the low-pH group than the control group (all P < 0.05). In contrast, in term fetuses, the total frequency, LF, and MF powers were significantly higher in the low-pH group than the control group (all P < 0.05). The area under the receiver operating characteristic of LF power to detect a low pH at birth was 0.794 in preterm fetuses and 0.595 in term fetuses. The specificity was 86.8% and 93.3% in preterm and term fetuses, respectively.

Conclusions

The changes in spectral power responding to a low pH are different between term and preterm fetuses. Spectral analysis of FHR variability may be useful fetal monitoring for early detection of fetal acidemia.     

Gender-specific heart rate dynamics in severe intrauterine growth-restricted fetuses

Background

Management of intrauterine growth restriction (IUGR) remains a major issue in perinatalogy.

Aims

The objective of this paper was the assessment of gender-specific fetal heart rate (FHR) dynamics as a diagnostic tool in severe IUGR.

Subjects

FHR was analyzed in the antepartum period in 15 severe IUGR fetuses and 18 controls, matched for gestational age, in relation to fetal gender.

Outcome measures

Linear and entropy methods, such as mean FHR (mFHR), low (LF), high (HF) and movement frequency (MF), approximate, sample and multiscale entropy. Sensitivities and specificities were estimated using Fisher linear discriminant analysis and the leave-one-out method.

Results

Overall, IUGR fetuses presented significantly lower mFHR and entropy compared with controls. However, gender-specific analysis showed that significantly lower mFHR was only evident in IUGR males and lower entropy in IUGR females. In addition, lower LF/(MF + HF) was patent in IUGR females compared with controls, but not in males. Rather high sensitivities and specificities were achieved in the detection of the FHR recordings related with IUGR male fetuses, when gender-specific analysis was performed at gestational ages less than 34 weeks.

Conclusions

Severe IUGR fetuses present gender-specific linear and entropy FHR changes, compared with controls, characterized by a significantly lower entropy and sympathetic-vagal balance in females than in males. These findings need to be considered in order to achieve better diagnostic results.     

Linear and complex heart rate dynamics vary with sex in relation to fetal behavioural states

BACKGROUND: A better understanding of gender influences on fetal heart rate can help to improve analysis of the latter and perhaps elucidate the increased risk of perinatal death that occurs in males. AIM: To assess differences in linear and complex heart rate dynamics according to fetal sex, in the antepartum period of normal term pregnancies, for patterns associated with fetal behavioural states. STUDY DESIGN AND SUBJECTS: One hundred and eighty seven fetal heart rate segments of 10-minute duration, acquired with a system for computerized analysis of cardiotocograms and classified into fetal behavioural patterns A, B, C or D were analysed. They had been acquired from 24 female and 23 male term fetuses, with uneventful perinatal outcomes. Four different comparative studies between female and male fetuses were conducted, considering different adjustments for gestational age, weight and FHR pattern. OUTCOME MEASURES: Indices of linear and nonlinear fetal heart rate variability, namely, long-term irregularity index, very low, low and high frequency spectral indices, approximate entropy and sample entropy. RESULTS: Pattern B was the most frequent, both in female and male fetuses. Pattern A was more likely to be associated to female than male fetuses, whereas the opposite occurred with patterns C and D. Linear indices were significantly higher in male than in female fetuses, whereas the opposite occurred with nonlinear indices. CONCLUSIONS: Male fetuses exhibited significantly more linear and significantly less complex fetal heart rate activity than female fetuses, expressing signs of a more active autonomous nervous system and of less active complexity control systems. These aspects may need to be considered when interpreting FHR tracings.     

Linear and nonlinear analysis of heart rate patterns associated with fetal behavioral states in the antepartum period

BACKGROUND: Fetal behavioral states are important indicators of fetal physiology and pathology associated to typical fetal heart rate (FHR) patterns. AIM: To provide linear and nonlinear analysis of FHR patterns associated with fetal behavioral states regarding a better understanding of these states and patterns. STUDY DESIGN AND SUBJECTS: Fifty FHR tracings from normal term pregnancies with a median duration of 40.3 min were acquired with the SisPorto 2.01 system for computerized analysis of cardiotocograms. Each tracing was divided into consecutive 10-minute segments and each segment was classified by two experts as pattern A, B, C or D. OUTCOME MEASURES: Linear and nonlinear indices were computed in each segment, namely mean FHR, long-term irregularity index (LTI), very low (VLF), low (LF) and high (HF) frequency spectral indices, approximate entropy (ApEn) and sample entropy (SampEn). Kappa statistic (kappa) and proportions of agreement (Pa) were used for assessment of inter-observer agreement. Bootstrap percentile confidence intervals and nonparametric statistical tests were calculated for statistical inference. RESULTS: Overall agreement between experts in pattern classification was good to excellent with values for kappa and Pa of 0.74 (95% CI: 0.64-0.94) and 0.94 (95% CI: 0.92-0.96), respectively. Most linear domain indices increased significantly with rising fetal activity whereas the opposite occurred with nonlinear indices, except for SampEn(2, 0.1). LF/(MF+HF) ratio also significantly increased with fetal activity, denoting an increased sympatho-vagal balance. CONCLUSIONS: Results support the hypothesis that entropy and linear variability indices measure different FHR features. FHR patterns associated with active sleep (B) and active wakefulness (D) evidenced more signs of autonomous nervous system activity, with sympatho-vagal imbalance, and less signs related to complexity or irregularity control systems than patterns associated with calm sleep (A) and calm wakefulness (C).     

Periodic spectral components of fetal heart rate variability reflect the changes in cord arterial base deficit values: a preliminary report

Fetal distress changes the function of the autonomic nervous system. These changes are reflected in the fetal heart rate and can be quantified with power spectrum analysis of heart rate variability. The purpose of this study was to find out whether spectral components of fetal heart rate variability (FHRV) during labor are associated with fetal cord arterial base deficit values at birth. The association between FHRV and umbilical cord arterial base deficit was studied in 14 singleton fetuses with normal pregnancy at 35–40 weeks of gestation. Fetal ECG was recorded by scalp-electrode using a STAN^® Fetal ECG monitor (Cinventa Ab, Mölndal, Sweden). FHRV was quantified by computing Fast-Fourier-transformed heart rate (HR) spectra at three frequency bands: low-frequency (LF) 0.03–0.07 Hz, mid-frequency (MF) 0.07–0.13 Hz and high-frequency (HF) 0.13–1.0 Hz. We found that total FHRV and MF FHRV were lower in fetuses with cord arterial base deficit 8 to 12 mmol/L in comparison to the fetuses with normal cord arterial base deficit value (P=0.02 and P=0.01, respectively). A linear correlation was found between the spectral densities and the cord arterial base deficit values (r=0.4 and r=0.6, respectively). We conclude that the results suggest changes in the autonomic nervous cardiac control in fetuses with cord arterial base deficit between 8 to 12 mmol/L. The clinical applicability of our observations on FHRV in predicting fetal distress remains to be further studied.     

Changes in fractal features of fetal heart rate during pregnancy

OBJECTIVE: Our objective was to examine whether heart rate time series of healthy normal fetuses possess fractal properties and, if so, to determine whether consistent changes in fractal features according to gestational age exist. DESIGN OF THE STUDY: One hundred nineteen fetal heart rate (FHR) recordings in 55 singleton pregnancies between the 22nd and 41st weeks were analyzed. Fractal analysis developed by Higuchi was performed. Changes of fractal dimension were examined according to gestational age. RESULTS: Two characteristic scaling regions were present in each FHR trace. The fractal dimension defined within 500 ms to 5 s (D(S); median 1.396, range 1.273-1.642) was lower than that defined longer than 30 s (D(L); median 1.933, range 1.492-2.049) in every case. These two values were significantly different (p<0.001). There was a statistically significant difference in the values of D(S) between (22-29 weeks, mean 1.323), (30-33 weeks, mean 1.443) (p=0.004), (34-35 weeks, mean 1.418) (p=0.002), (36 weeks, mean 1.409) (p=0.030), (37-38 weeks, mean 1.394) (p=0.006), and (40-41 weeks, mean 1.452) (p=0.001), respectively. D(S) values between (40-41 weeks), (37-38 weeks) (p=0.012), and (39 weeks, mean 1.369) (p=0.030), respectively, were also significantly different. The values of D(L) decreased from 22-39 weeks (median 1.941) to 40-41 weeks (median 1.891) (p=0.008). CONCLUSIONS: Two distinct fractal structures within the FHR variation were identified. Fractal features of heart rate of healthy normal fetuses change significantly during pregnancy period. Fractal analysis may be useful for evaluating FHR variation.     

Power spectrum analysis of fetal heart rate variability at near term and post term gestation during active sleep and quiet sleep

Background

Spectral analysis of fetal heart rate variability is promising for assessing fetal condition. Before using spectral analysis for fetal monitoring it has to be determined whether there should be a correction for gestational age or behavioural state.

Aims

Compare spectral values of heart rate variability between near term and post term fetuses during active and quiet sleep.

Study design

Case-control. Cases had a gestational age of ≥ 42 weeks; controls were 36 to 37 weeks. Fetuses were matched for birth weight percentile.

Subjects

STAN^® registrations from healthy fetuses. For each fetus one 5-minute segment was selected during active and one during quiet sleep.

Outcome measures

Absolute and normalized low (0.04-0.15 Hz) and high frequency power (0.4-1.5 Hz) of heart rate variability.

Results

Twenty fetuses were included. No significant differences were found between cases and controls in absolute (481 and 429 respectively, P = 0.88) or normalized low (0.78 and 0.80 respectively, P = 0.50) or absolute (41 and 21 respectively, P = 0.23) or normalized high frequency power (0.08 and 0.07 respectively, P = 0.20) during active state. During rest, normalized low frequency power was lower (0.58 and 0.69 respectively, P = 0.03) and absolute (16 and 10 respectively, P = 0.04) and normalized high frequency power were higher (0.21 and 0.14 respectively, P = 0.01) in cases compared to controls. Absolute and normalized low frequency power were higher during active state compared to rest in both groups (all P values < 0.05).

Conclusions

We found sympathetic predominance during active state in fetuses around term. Post term parasympathetic modulation during rest was increased compared to near term.     

Aerobic exercise during pregnancy influences fetal cardiac autonomic control of heart rate and heart rate variability

Background

Previous studies using ultrasound technology showed that fetal heart rate (HR) may be responsive to maternal aerobic exercise. Although it is recognized that cardiac autonomic control may be influenced by the intrauterine environment, little is known about how maternal exercise affects fetal heart development.

Aims

This study tested the hypothesis that regular maternal exercise throughout gestation influences fetal cardiac autonomic control of HR and heart rate variability (HRV) when compared to fetuses of non-exercising women.

Study design

Magnetocardiograms (MCGs) were recorded using a dedicated fetal biomagnetometer at 28, 32 and 36 weeks gestational age (GA) from 26 regularly exercising (> 30 min of aerobic exercise, 3× per week) and 35 healthy, non-exercising pregnant women. Fetal MCG was isolated and normal R-peaks were marked to derive fetal HR and HRV in the time and frequency domains. We applied a mixed-effects model to investigate the effects of exercise, GA and fetal activity state.

Results

At 36 weeks GA, during the active fetal state, fetal HR was significantly lower in the exercise group (p = < 0.0006). Post-hoc comparisons showed significantly increased HRV in the exercise group during the active fetal state at 36 weeks GA for both time and frequency domain measures.

Conclusion

These results indicate that regular maternal exercise throughout gestation results in significantly lower fetal HR and increased HRV.     

Nonlinear analyses of heart rate variability in normal and growth-restricted fetuses

BACKGROUND: Many studies on the physiology of the cardiovascular system reported that nonlinear chaotic dynamics may govern the generation of the heart rate signal. OBJECTIVE: To examine whether the heart rate dynamics of an intrauterine growth restricted (IUGR) fetus is different from a healthy normal fetus by nonlinear methods of time series analysis. DESIGN OF THE STUDY: One hundred nineteen fetal heart rate (FHR) recordings from healthy normal fetuses, and 69 recordings from IUGR fetuses were analyzed. Nonlinear analyses included attractor reconstruction, calculation of the largest Lyapunov exponents using the Wolf algorithm, and estimation of correlation dimension. The largest Lyapunov exponents from normal fetuses were checked by means of surrogate-data test. RESULTS: Abnormal FHR patterns of IUGR fetuses such as decreased variability and repetitive late decelerations presented a remarkably different structure in the reconstructed attractor. Surrogate data suggest that the FHR of healthy normal fetuses has unique nonlinear characteristics. The largest Lyapunov exponents were positive for all of 119 healthy normal fetuses, indicating that the FHR control system is sensitive to initial conditions. The values of IUGR fetuses were significantly lower than those of normal subjects. In normal fetuses, significant changes of correlation dimension according to gestational age were observed. In IUGR fetuses, however, such changes were not found. CONCLUSIONS: The heart rate dynamics of IUGR fetuses is less chaotic than that of normal fetuses. Decreased system complexity suggested by correlation dimension may limit the IUGR fetuses' ability to maintain cardiovascular integrity, and therefore, to adapt to the variety of internal and external cardiovascular stresses.     

Relationship between age and heart rate variability in supine and standing postures: A study of spectral analysis of heart rate

Summary We compared heart rate variability measures of 11 normal children (4–12 years) to 23 normal adults (21–43 years) to study the effect of age on heart rate variability measures. Children had a significantly higher supine and standing heart rate and lower supine and standing systolic diastolic blood pressure. Children also had a significantly higher supine standard deviation of HR, supine low frequency (0.01–0.05 Hz) (p<0.005), supine high frequency (0.2–0.5 Hz) (p<0.001), and standing high frequency powers (p<0.005) compared to adults. The ratio of mid frequency (0.07–0.15 Hz) to high frequency power (0.2–0.5 Hz) upon standing was significantly lower in children (p<0.005). While there was a significant increase of the mid frequency power from supine to standing posture in the adult group (p<0.02), there was no such significant increase in children. There were also significant negative correlations between age and supine low frequency, mid frequency, and high frequency powers, and standing high frequency power. These findings illustrate a decrease of cholinergic and an increase of adrenergic modulation of heart rate variability with age (4–43 years).     

Quantitative comparison of entropy analysis of fetal heart rate variability related to the different stages of labor

Background

The interpretation of the fetal heart rate (FHR) signal considering labor progression may improve perinatal morbidity and mortality. However, there have been few studies that evaluate the fetus in each labor stage quantitatively.

Aim

To evaluate whether the entropy indices of FHR are different according to labor progression.

Study design

A retrospective comparative study of FHR recordings in three groups: 280 recordings in the second stage of labor before vaginal delivery, 31 recordings in the first stage of labor before emergency cesarean delivery, and 23 recordings in the pre-labor before elective cesarean delivery.

Subjects

The stored FHR recordings of external cardiotocography during labor.

Outcome measures

Approximate entropy (ApEn) and sample entropy (SampEn) for the final 2000 RR intervals.

Results

The median ApEn and SampEn for the 2000 RR intervals showed the lowest values in the second stage of labor, followed by the emergency cesarean group and the elective cesarean group for all time segments (all P < 0.001). Also, in the second stage of labor, the final 5 min of 2000 RR intervals had a significantly lower median ApEn (0.49 vs. 0.44, P = 0.001) and lower median SampEn (0.34 vs. 0.29, P < 0.001) than the initial 5 min of 2000 RR intervals.

Conclusions

Entropy indices of FHR were significantly different according to labor progression. This result supports the necessity of considering labor progression when developing intrapartum fetal monitoring using the entropy indices of FHR.     

Diurnal rhythms in fetal heart rate baseline and sustained fetal tachycardia in twin pregnancy

OBJECTIVE: To elucidate the synchronization of phases of diurnal rhythms in fetal heart rate (FHR) baseline between twin fetuses and the occurrence of sustained fetal tachycardia. METHODS: FHR was simultaneously recorded in twins for 24 h in 7 monochorionic diamniotic (MD) and 8 dichorionic diamniotic (DD) twin pregnancies at 35 to 38 weeks of gestation. The diurnal rhythms of the hourly mean FHR baseline were tested in each fetus, and the time of occurrence of sustained fetal tachycardia was compared between twins. The correlation coefficients and phase lags of diurnal rhythms between the hourly mean FHR baselines of twins were calculated in each case. RESULTS: There were significant diurnal rhythms in the hourly mean FHR baselines of all twin fetuses (p<0.01). The patterns of diurnal rhythms were similar for each pair of twins, with the exception of the periods of sustained fetal tachycardia. Sustained fetal tachycardia was not coincident between twins. Analysis in which the periods of sustained fetal tachycardia were excluded demonstrated a significant correlation between the hourly mean FHR baselines of twins in all cases (p<0.01). In the case of DD twins, the phase lag between twins was 0; however, phase lags were observed in 4 cases of MD twins. CONCLUSIONS: The results of this study revealed that the diurnal rhythms in the FHR baseline correlated well between twins, and that the occurrences of sustained fetal tachycardia were completely independent.     

Computerized fetal heart rate monitoring after vibroacoustic stimulation in the anencephalic fetus

Background

To quantify changes in fetal heart rate (FHR) parameters after vibroacoustic stimulation (VAS) and to evaluate the usefulness of VAS testing (VAST) in anencephalic fetuses. Our findings may also help to clarify the route(s) of vibration and sound transmission during VAST.

Study design and subjects

We obtained the antepartum FHR tracings of 16 anencephalic fetuses, including both the nonstress test (NST) and VAST. Using a computerized monitoring system, HYFM, we determined all FHR parameters from data collected for 10 min before and 10 min after VAS, at successive gestational stages.

Results

We observed three false reactive responses at term. The false reactive rate for VAST (3/16) was higher than that for NST (1/16). No FHR parameters increased significantly after VAS except for the number of fetal movements (FM), which increased significantly in all gestational groups (25th-32nd and 33rd-40th weeks).

Conclusions

These findings call attention to an increased probability of a false reactive response in VAST analysis, when the fetus is affected by a CNS disorder. Increased numbers of FM after VAS suggest that the vibratory pathway is more likely to elicit fetal response than the auditory pathway in this setting, and that the vibratory stimulation travels by subcortical rather than by cortical pathways.     

正常儿童动态心电图窦性心率及心率变异分析

目的探讨正常儿童心率及心率变异性(HRV)特点。方法对804例正常儿童进行24h全程动态心电图检查,分析心率及HRV。结果不同年龄儿童窦性心率范围不同,年龄越小心率越快;儿童不同性别间HRV中24h内全部正常心动周期的标准差(SDNN)、24h内每5minNN间期标准差的平均值(SDNNindex)、NN50占所有N-N间期个数的百分数(PNN50)、极低频率(VLF)、低频(LF)差异有显著性;儿童不同年龄组间24h内5min节段平均心动周期的标准差(SDANN)、VLF、LF、全程相邻NN间期之间的均方根值(rMSSD)差异有显著性;儿童组与成人正常参考值中SDNN、SDANN、rMSSD差异有显著性,rMSSD儿童组中明显高于成人组。结论HRV是一种反映自主神经活性及其平衡的能定量、可重复的非侵入性的检测方法,是自主神经系统与心血管系统相互制约的结果。不同年龄、不同性别间儿童HRV存在显著差异;儿童组与成人参考值存在显著差异,尤其rMSSD儿童明显高于成人,提示儿童的自主神经功能较成人活跃,而随着年龄增长自主神经功能减退,尤其是迷走神经的紧张抑制功能明显减退。     

小儿扩张型心肌病心率变异性分析

目的分析扩张型心肌病(DCM)儿童的心率变异性(HRV)。方法DCM儿童23例(研究组),匹配健康儿童23例为对照(对照组)。采用康泰TLC3000A12通道动态心电图(EKG)分析系统描记24hEKG,分析心率、HRV的时域指标和频域指标。应用SPSS11.0软件进行统计学处理。结果与对照组比较,研究组最低心率明显增高(P<0.05),最高心率稍增高(P>0.05);HRV时域指标SDNN、SDANN、pNN50明显降低(P<0.05),rMSSD稍降低(P>0.05);HRV频域指标TP、ULF明显降低(P<0.05),VLF、LF、HF、LF/HF稍增高(P>0.05)。结论DCM儿童自主神经功能明显受损。     

Insight into variable fetal heart rate decelerations from a mathematical model

During labor and delivery, variable decelerations in the fetal heart rate (FHR) are commonly seen on the cardiotocogram (CTG) that is used to monitor fetal welfare. These decelerations are often induced by umbilical cord compression from uterine contractions. Via changes in oxygenation and blood pressure, umbilical cord compression activates the chemo- and baroreceptor reflex, and thus affects FHR. Since the relation between the CTG and fetal oxygenation is complex, assessment of fetal welfare from the CTG is difficult.     

血管迷走性晕厥儿童心率变异性分析

目的探讨血管迷走性晕厥(VVS)儿童的心率变异性(HRV)。方法对27例不明原因晕厥患儿经直立倾斜试验(HUTT)检查阳性并诊断为VVS的HRV进行分析(研究组),并将29例健康儿童作为对照(对照组)。采用康泰TLC3000A12通道动态心电图分析系统描记未发生晕厥时24h心电图,分析时域指标和频域指标,应用SPSS11.0软件进行统计学处理。结果研究组低频功率(LF)与对照组比较明显降低(P<0.05);频域指标与时域指标在不同年龄段差别不明显(P>0.05);女性时域指标中SDANN及VLF、LF较男性明显降低(P<0.05);血管抑制型与混合型VVS的HRV指标差异不明显。结论VVS儿童基础自主神经功能发生改变;HRV主要受性别影响,而年龄影响不明显;HUTT不同反应类型VVS的HRV不存在差别。     

Comparison of fetal heart rate patterns using nonlinear dynamics in breech versus cephalic presentation at term

Background

It has been reported that breech fetuses have inferior neurological outcomes regardless of mode of delivery, raising the possibility that in utero neurological impairment is more frequent in breech fetuses, possibly contributing to malpresentation.

Aims

To assess differences between the cardiovascular autonomic nervous systems (ANSs) of breech and cephalic fetuses using nonlinear dynamic indices of fetal heart rate (FHR) variability.

Study design and subjects

This study included 86 fetuses with breech presentation and 173 fetuses with cephalic presentation, with no other maternal or fetal problems. We analyzed FHR variability and spectral indices as markers of ANS behavior. We used nonlinear dynamic indices to represent the complexity of heart rate regulation, as well as correlation dimension as a chaotic index of the cardiovascular control system.

Results

One of FHR parameters (Mean minute range) was significantly lower in breech than cephalic fetuses (p = 0.0294). However, there were no other significant differences in any linear or nonlinear indices, nor in clinical outcomes, between breech and cephalic fetuses.

Conclusion

Our data suggest that breech fetuses have neither more active ANS nor less active complexity control systems than do cephalic fetuses. This indicates that the neurologic maturation of breech fetuses is not inferior to cephalic ones. The practical implication of these findings is that the nervous system integrity of breech fetuses may not result directly in neonatal complications.     

Measures of and changes in heart rate variability in pediatric heart transplant recipients

Heart rate variability is primarily regulated by the autonomic nervous system. Heart transplant recipients undergo surgical denervation of the graft, which results in interruption of autonomic innervation with resultant diminished heart rate variability although some degree of autonomic control may return. This study aimed to characterize heart rate variability in this population. We report a retrospective review of Holter monitor data from transplanted patients between 2005 and 2013. Studies with significant atrial or ventricular arrhythmias were excluded. We evaluated changes over time and compared standard time domain measures to published pediatric normal values. Data were reviewed from 582 monitors in 152 patients. We found that pediatric heart transplant recipients have lower heart rate variability than age‐matched controls and higher average heart rate in recipients older than 3 years. There is an increase in measures of variability through the first 3 years post‐transplant with plateau after that time. Surgical technique in regard to interruption of the vagus nerve does not affect variability, nor does underlying congenital vs acquired heart disease.