Short-term variability of fetal heart rate during pregnancies with normal and insufficient placental function

Relative uteroplacental insufficiency of labor

Relative uteroplacental insufficiency of labor (RUPI-L) is a clinical condition that refers to alterations in the fetal oxygen "demand-supply" equation caused by the onset of regular uterine activity. The term RUPI-L indicates a condition of "relative" uteroplacental insufficiency which is relative to a specific stressful circumstance, such as the onset of regular uterine activity. RUPI-L may be more prevalent in fetuses in which the ratio between the fetal oxygen supply and demand is already slightly reduced, such as in cases of subclinical placental insufficiency, post-term pregnancies, gestational diabetes, and other similar conditions. Prior to the onset of regular uterine activity, fetuses with a RUPI-L may present with normal features on the cardiotocography. However, with the onset of uterine contractions, these fetuses start to manifest abnormal fetal heart rate patterns which reflect the attempt to maintain adequate perfusion to essential central organs during episodes of transient reduction in oxygenation. If labor is allowed to continue without an appropriate intervention, progressively more frequent, and stronger uterine contractions may result in a rapid deterioration of the fetal oxygenation leading to hypoxia and acidosis. In this Commentary, we introduce the term relative uteroplacental insufficiency of labor and highlight the pathophysiology, as well as the common features observed in the fetal heart rate tracing and clinical implications.

Effect of Age on Heart Rate Variability in Patients with Mitral Valve Prolapse: An Observational Study

Age is an important determinant of heart rate variability (HRV) in healthy individuals. The incidence of arrhythmia is high in patients with mitral valve prolapse (MVP). However, the correlation of HRV in patients with MVP in different age groups is not well established. We presumed that increasing age would be prospectively associated with declining HRV measurement in MVP. Sixty patients with MVP and 120 control individuals were included and underwent 24 h HRV analysis. No significant difference was found in all parameters calculated in the time domain or in the frequency domain between the two groups. However, as patients' age increased, a significant time domain (SDNN, RMSSD, NN50, and pNN50) decline was found in the MVP group, but not in the control group. This suggests that patients with MVP may have autonomic nervous system involvement that increases the risk of arrhythmia and heart disease with increasing age.

A systematic review on the utility of non-invasive electrophysiological assessment in evaluating for intra uterine growth restriction

Background

Non-invasive electrophysiological assessment (NIEA) is an evolving area in fetal surveillance and is attracting increasing research interest. There is however, limited data outlining its utility in evaluating intra uterine growth restriction (IUGR). The objective of this study was to carry out a systematic review to outline the utility of NIEA parameters in evaluating IUGR.

Methods

A systematic review of peer reviewed literature was performed, searching PUBMED, Ovid MEDLINE and EMBASE. The outcomes of interest included NIEA parameters [P wave duration, PR interval, QRS duration, QT interval, T/QRS ratio, short term variability (STV) and long term variability (LTV)] and a descriptive summary of relevant studies as well.

Results

Sixteen studies were identified as suitable for inclusion. The utility of NIEA parameters were investigated in tabular form. In particular, QRS and QT duration, T/QRS ratio, STV and PRSA analysis displayed utility and merit further consideration in evaluating for IUGR. Issues identified in the review were in relation to variances in definition of IUGR, small sample sizes and the lack of technological consistency across studies.

Conclusion

NIEA shows promise as an adjunct surveillance tool in fetal diagnostics for IUGR. Larger prospective studies should be directed towards establishing reliable parameters with a focus on uniformity of IUGR definition, technological consistency and the individualisation of NIEA parameters.

Electronic supplementary material

The online version of this article (10.1186/s12884-019-2357-9) contains supplementary material, which is available to authorized users.

Recognition of chronic hypoxia and pre-existing foetal injury on the cardiotocograph (CTG): Urgent need to think beyond the guidelines

Chronic utero-placental insufficiency may result in progressive hypoxia culminating in fetal decompensation and acidosis and this is termed 'chronic' or 'long-standing' hypoxia. It is essential to recognise the features of chronic hypoxia on the CTG trace so as to institute timely and appropriate action. The current guidelines may not capture a fetus who starts labour already compromised or limited in its ability to compensate for hypoxic or mechanical stresses during labour. The aim of this short review is to explore the CTG features that allow the clinician to recognise a fetus who may present with an antenatal insult such as chronic hypoxia, anaemia, infection, fetal arrhythmias and preexisting non-hypoxic brain injury.

Fetal heart rate and umbilical artery flow velocity variability in intrauterine growth restriction: a matched controlled study

OBJECTIVES

To study heart rate and umbilical artery blood flow velocity variability in growth-restricted fetuses and investigate the influence of the autonomic nervous system on these parameters.

METHODS

Doppler velocity waveforms were collected from long-lasting umbilical artery recordings in 15 fetuses with growth restriction and 15 normal age-matched controls at 23-35 weeks of gestation. Absolute heart rate and umbilical artery blood flow velocity as well as the coefficient of variation were determined. Using power spectral analysis the low- and high-frequency bands of heart rate variability and blood flow velocity variability were calculated. The low-to-high (LH) ratio of heart rate variability and blood flow velocity variability were examined as a measure of sympathovagal balance.

RESULTS

In growth-restricted fetuses umbilical artery velocities were significantly reduced. Heart rate variability was significantly reduced in the presence of growth restriction, but no significant difference was demonstrated for blood flow velocity variability. The LH ratio for heart rate variability was significantly decreased in growth restriction, but no difference in LH ratio was demonstrated for blood flow velocity variability.

CONCLUSION

Flow velocity variability in growth restriction seems not to be predominantly influenced by the autonomic nervous system, whereas the decreased heart rate variability seems to be influenced by altered sympathetic-parasympathetic balance.

Fractal fluctuations in cardiac time series

Human heart rate, controlled by complex feedback mechanisms, is a vital index of systematic circulation. However, it has been shown that beat-to-beat values of heart rate fluctuate continually over a wide range of time scales. Herein we use the relative dispersion, the ratio of the standard deviation to the mean, to show, by systematically aggregating the data, that the correlation in the beat-to-beat cardiac time series is a modulated inverse power law. This scaling property indicates the existence of long-time memory in the underlying cardiac control process and supports the conclusion that heart rate variability is a temporal fractal. We argue that the cardiac control system has allometric properties that enable it to respond to a dynamical environment through scaling.

Effect of age on long-term heart rate variability

OBJECTIVE

Previous studies on short-term time series of heart rage suggest an inverse relationship between age and spectral powers of heart rate variability in various frequency bands. In this study, we examined the relationship between age (6-61 years) and long-term heart rate variability.

METHODS

We obtained 24-h Holter ECG in 33 healthy human subjects (11 children and 22 adults). The heart rate data were analyzed by using spectral analysis and fractal dimensions of the time series.

RESULTS

We found a significant negative correlation between age and very low frequency (VLF, 0.0033-0.04 Hz), low frequency (LF, 0.04-0.15 Hz) and high frequency (HF, 0.15-0.5 Hz) powers and fractal dimensions during awake as well as sleep periods, and a positive correlation between age and LF/HF ratios. Age and ultra-low frequency (ULF, < 0.0033 Hz) were modestly and negatively correlated only during the awake period.

CONCLUSIONS

Sleep ULF power is not significantly affected by age, whereas VLF, LF and HF powers and fractal dimensions of heart rate significantly decrease with age during awake as well as sleep periods.

Fetal heart rate patterns in growth-restricted fetal sheep induced by chronic fetal placental embolization

OBJECTIVE

Our purpose was to test the hypothesis that chronic placental insufficiency and intrauterine growth restriction in fetal sheep causes a decrease in the number of fetal heart rate accelerations and fetal heart rate variability.

STUDY DESIGN

Chronically catheterized fetal sheep were embolized (n = 6) daily with 15 to 50 microns latex microspheres for 21 days between 0.74 and 0.88 of gestation into the abdominal aorta, until fetal arterial oxygen content was decreased by 40% to 50% of the preembolization value. Control animals (n = 6) received saline solution only. Signals from chest electrodes were analyzed on-line with the Sonicaid System 8000 in 2-hour epochs every 6 hours starting at 8 AM over the first 48 hours of hypoxemia and for 2 hours between 8 and 10 AM every other day from day 3 to day 21 of hypoxemia. Umbilical artery Doppler-derived resistance index and fetal plasma catecholamine concentrations were also measured.

RESULTS

Embolized fetuses had asymmetric intrauterine growth restriction and became chronically hypoxemic (p < 0.001) with a progressive increase in the umbilical artery resistance index (p < 0.001). During the first 48 hours of hypoxemia the number of accelerations and decelerations and both short- and long-term fetal heart rate variability increased initially, followed by a return to control levels by 20 hours after the onset of embolization. After 21 days of hypoxemia the number of accelerations was significantly reduced by 30% compared with controls (p < 0.05). Both short- and long-term fetal heart rate variability in control fetuses gradually increased with advancing gestational age (p < 0.001 and p < 0.01, respectively), whereas in embolized fetuses the fetal heart rate variability remained unchanged and was 20% lower than that of controls on day 21 (both p < 0.01).

CONCLUSION

Intrauterine growth restriction and long-term hypoxemia in fetal sheep are associated with a decrease in short- and long-term fetal heart rate variability, possibly because of a delay in the normal maturational changes of the autonomic control of fetal heart rate.

Sodium lactate increases sympathovagal ratios in normal control subjects: spectral analysis of heart rate, blood pressure, and respiration

We used spectral analysis of heart rate (HR), blood pressure (BP), and respiration to examine the effects of lactate on cholinergic and adrenergic influences on HR and BP variability, a technique found to be very useful in cardiovascular research. We specifically used high frequency (0.2-0.5 Hz) and midfrequency (0.07-0.15 Hz) powers to study cholinergic and adrenergic activity in nine normal control subjects before and after lactate and placebo infusions. Our results demonstrate a marked decrease in cholinergic activity and a significant increase in sympathovagal ratios of HR modulation after lactate infusions. This altered sympathovagal balance may contribute to the panicogenic effects of lactate in panic disorder patients.

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

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 and 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).

Decreased heart rate variability in panic disorder patients: a study of power-spectral analysis of heart rate

We have previously found decreased standard deviations and mean consecutive differences of R-R intervals in panic disorder patients in standing posture, compared with control subjects. In the present study, we used spectral analysis of heart rate variability to examine autonomic function in 21 panic disorder patients and 21 normal control subjects. Patients had a significantly lower standard deviation of heart rate in supine as well as standing postures. Absolute low frequency power (0.01-0.05 Hz) was also significantly lower in panic disorder patients in standing postures. Upon standing, the panic disorder patients had significantly higher relative mid-frequency power (0.07-0.15 Hz). During a standing deep-breathing condition at six breaths per minute, the patients had a significantly decreased absolute and relative mid-frequency (0.07-0.15 Hz) power compared with control subjects. These findings suggest a decrease in cholinergic and a relative increase in adrenergic responsiveness in panic disorder patients compared with control subjects.

Is fetal heart rate monitoring sufficiently sensitive to detect changes during labour?

Although fetal monitoring is a common clinical procedure, there is little quantitative evidence that it can detect changes occurring during labour. We present quantitative data comparing the first and second stage of labour, from 21 labours resulting in a normal fetal outcome. A range of fetal heart rate variables was calculated from the output of a fetal heart rate monitor. Significant changes were detected in baseline fetal heart rate (P less than 0.005), heart rate variability (P less than 0.05), number of dips (P less than 0.01) and their depth (P less than 0.01). The results encourage confidence in the sensitivity of fetal monitoring for the detection of changes in a number of fetal heart rate variables during the course of labour.

Heart rate variability in patients with major depression

We have previously reported decreased heart rate variability upon standing in panic disorder patients compared with controls. In this study, we extend our report to include patients with major depression (n = 19). Compared to normal controls (n = 20) and panic disorder patients (n = 30), there was no significant difference in the immediate changes in heart rate upon standing in the depressed group. The standing heart rate variability (R-R variability) was significantly lower in panic disorder patients compared to both normal controls and depressed patients as indicated by the corrected standard deviations, the corrected mean consecutive difference, the corrected standard deviation of the mean consecutive difference of the R-R intervals, and the high frequency variability in successive R-R intervals, suggesting an increased vagal withdrawal in panic disorder patients, especially upon standing. There was no significant difference in any of the heart rate variability measures between depressed patients and normal controls.

An application of fractal dimension to the detection of transients in the electroencephalogram

It is sometimes desirable to identify a brief seizure, occasional spike, single evoked potential, or other transient in the EEG. Transient detection in an EEG can be a difficult task, often requiring prior knowledge of the characteristics of the transient. A fractal is a shape which retains structural detail despite magnification (scaling). The complexity of the structure of such a set, invariant under this scaling, can be characterized by a single number: the fractal dimension. Regarding the EEG as a fractal, we have shown that transient deterministic data in the EEG have a fractal dimension different from the quasirandom background. An extensive introduction to fractals is presented with the assumption that the reader is unfamiliar with the theory. In the preliminary results presented here, analysis by fractal dimension is shown to be a promising method of transient detection, requiring no prior knowledge of the characteristics of the transient. Possible applications of the technique to evoked potential technology and epilepsy surgery are discussed. Other applications to biology, neuroscience and medicine are reviewed.

The influence of physiological parameters on long term heart rate variability in healthy preterm infants

The instantaneous heart rate shows a variation around the mean heart rate caused by cardioregulatory mechanisms which are mediated through the sympathetic and vagal autonomic nervous system. To gain more insight into the influence of physiological parameters on neonatal heart rate variability a study was performed in four healthy preterm newborns during the first five days of life. Instantaneous heart rate, respiration rate, transcutaneous pO2, blood pressure and behaviour were recorded during 40 minutes four times a day. Long term heart rate variability was calculated as the difference between p95 and p5 of instantaneous heart rate values sampled during three minutes. A clear relationship between long term variability and age (maturity of the autonomic nervous system), respiration rate (respiratory sinus arrhythmia or a tidal volume mediated effect) and behaviour (increase of sympathetic tone during REM sleep) was found. No influence of blood pressure, heart rate, and transcutaneous pO2 within physiological ranges could be detected. The relative influence of the different physiological parameters on heart rate variability has to be established before the value of heart rate variability as a monitoring tool in neonatal intensive care can be investigated.

Applications of nonlinear dynamics to clinical cardiology

(1) Nonlinear mechanisms may apply both to the understanding of SA-AV node interactions and to bifurcations leading to certain types of AV block. (2) The fractal His-Purkinje system serves as the structural substrate for the generation of the broadband, inverse power-law spectrum of the stable ventricular depolarization (QRS) waveform. (3) Fractal anatomy is also seen in multiple other systems: pulmonary, hepatobiliary, renal, etc. Fractal morphogenesis may reflect a type of critical phenomenon that results in the generation of these irregular, but self-similar structures. (4) Self-similar (fractal) scaling may underlie the 1/f-like spectra seen in multiple systems (e.g., interbeat interval variability, daily neutrophil fluctuations). This fractal scaling may provide a mechanism for the "constrained randomness" that appears to underlie physiological variability and adaptability. (5) Behavior consistent with subharmonic bifurcations is seen in cardiac electrophysiology (e.g., sick sinus syndrome) and hemodynamic perturbations (e.g., swinging heart phenomenon in pericardial tamponade). (6) Ventricular tachyarrhythmias associated with sudden cardiac death (e.g., torsades de pointes, ventricular fibrillation) appear to reflect relatively periodic, not chaotic (turbulent) processes resulting from disruption of the physiologic fractal depolarization sequence. (7) Spectral analysis of Holter monitor data may help in the detection of patients at high risk for sudden death.

Fetal heart rate patterns and perinatal outcome of very-low-birthweight infants

The obstetric records of 125 infants weighing 500-1250 g who were born in 1978 and 1979 at the Helsinki University Central Hospital were studied retrospectively to find out any associations between fetal heart rate (FHR) patterns and perinatal outcome. FHR recordings of 79 fetuses were available for study. Normal reactive patterns were observed in nine, nonreactive in 54, decelerations in 58, silent patterns in 45 and combined distress patterns in 36 fetuses. The interval from the first pathological sign to delivery was up to 27 days. Five fetuses in the monitored group died in utero, 26 infants died neonatally and two later. The risk of neonatal death after pathological FHR patterns was lower than after an FHR pattern without abnormality. Idiopathic respiratory distress syndrome (RDS) was diagnosed in 32 infants, of whom 16 died. Forty-seven fetuses (59%) of the monitored group were delivered abdominally and 32 vaginally. The risk of RDS was not significantly associated with FHR patterns and mode of delivery. We conclude that unlike term fetuses, low-birthweight fetuses seem to benefit from a period of intrauterine stress reflected in abnormal FHR patterns, if caesarean section is used liberally.

Comprehensive fetal monitoring by microcomputer--a clinical approach

An inexpensive microcomputer has been devised to analyze fetal heart signals and fetal activity which were simultaneously recorded. Digital techniques were used to provide quantitative analysis of each of these inputs, and the interrelations among them. A parallel graphical presentation of those inputs was also provided.

Reduced short-term variability of fetal heart rate in association with maternal hyperglycemia during pregnancy in insulin-dependent diabetic women

The differential index, which describes the short-term component of fetal heart rate variability, and maternal blood glucose levels were measured 109 times in 19 insulin-dependent diabetic mothers in the second half of gestation. An abnormal differential index was observed more often with maternal hyperglycemia (11/45) than with normoglycemia (5/64). A significant negative linear correlation was found between the differential index and the blood glucose level of the mother.

Antepartum fetal heart rate variability and intervillous placental blood flow in association with smoking

Intervillous placental blood flow and indices of fetal heart rate variability were measured from seven healthy pregnant women in the last trimester of pregnancy, once before and twice after smoking one cigarette. A blood flow reduction was observed in seven, a rise in five, and no change in two measurements. When intervillous placental blood flow decreased both indices of variability decreased (p less than 0.001), and when it increased the short-term component of fetal heart rate variability increased more significantly (p less than 0.001) than did the long-term component (p less than 0.01).

Short term variability of fetal heart rate during pregnancies complicated by hypertension

The clinical significance of the differential index (DI), which describes the short term variability of fetal heart rate (FHR), in fetal surveillance was assessed in 202 hypertensive pregnancies. The analyses of FHR variability were made by a microprocessor-based on-line method using the abdominal fetal electrocardiogram as a triggering signal. The analysis was successful in 258 out of 323 trials (80%). Five perinatal deaths (2.5%) occurred in the whole series. Fetal distress developed in 47 out of 137 patients who had a successful FHR analysis within 1 week of delivery. The sensitivity of the antepartum DI in predicting fetal distress in labour was 46%, predictive value was 88% and specificity 97%. The risk of intrapartum fetal distress after a pathological DI was 4 times that after a normal DI (relative risk), which is highly significant.

Short term variability of fetal heart rate during insulin-dependent diabetic pregnancies

The clinical significance of quantified short term variability of antepartal fetal heart rate (FHR) in prediction of fetal distress in labor was assessed in 120 insulin-dependent diabetic pregnancies. FHR was recorded by abdominal fetal electrocardiography (aFECG), from which the differential indices (DI) describing the short term variability of FHR were analyzed by a microprocessor-based on-line method. The analysis was successful in 308 of 350 trials (87%). In ten pregnancies, no acceptable a FECG was obtained. Fetal distress developed in 28 of the 110 pregnancies with successful FHR analysis. There were no intrauterine deaths in this series, but two newborn infants died (perinatal mortality 1.7%). Ninety-three pregnancies with FHR analyses within one week of delivery were included in the assessment of the test. DI predicted 2 of the 17 cases of fetal distress (sensitivity 67%). Twelve of the 18 cases with a pathological DI developed fetal distress (predictive value 71%). DIs were normal in 67 of the 73 pregnancies without fetal distress (specificity 92%). Risk of fetal distress after a pathological DI was 8.5 times that after normal DIs (relative risk), which is highly significant.

Significant correlation between maternal hemodynamics and fetal heart rate variability

The differential index, describing the short-term component, and the interval index, describing the long-term component, of fetal heart rate variability were measured by an on-line method from the abdominal electrocardiograms of eight fetuses during the third trimester of normal pregnancies while mothers were smoking a cigarette. Maternal heart rate and maternal blood pressure were measured intermittently before, during, and after smoking. Analyses of fetal heart rate variability were performed continuously with the sample time of 1 minute during the experiments. An increase in maternal heart rate and blood pressure, with concomitant decrease in the interval index and the differential index, was observed. The correlation analysis revealed a negative correlation between maternal heart rate and the interval index (p less than 0.001), between diastolic pressure and the differential index (p less than 0.01), and between systolic pressure and the differential index (p less than 0.01).

Fetal anemia and heart rate patterns

A retrospective survey was performed of the clinical records and cardiotocograms (CTG) of fetuses born in 1978 and 1979 at Helsinki University Central Hospital with hemoglobin concentration less than 170 g/liter in peripheral blood or umbilical artery. Eighty-three fetuses (0.7%) had thus defined anemia. Thirty-eight of them had late decelerations, 29 silent and nine sinusoidal fetal heart rate (FHR) patterns. Late decelerations and sinusoidal patterns were significantly more often associated with severe (hemoglobin concentration less than 80 g/liter) than with moderate anemia. The fetal outcome in terms of perinatal death and low APGAR scores after sinusoidal pattern was poorer than without this pattern, but the difference was not statistically significant. It is concluded that intermittent sinusoidal FHR pattern with late decelerations is suggestive of fetal anemia.

Short-term variability of fetal heart rate in cholestasis of pregnancy

Maternal cholestasis affects about 1% of pregnancies in Finland. Although maternal prognosis in obstetric cholestasis is always good, an increased fetal risk has been reported by several authors. In this paper the differential index (DI), describing the short-term variability of fetal heart rate, was measured in 64 pregnancies with colestasis of pregnancy by a microprocessor-based "on-line" method, which uses abdominal fetal electrocardiogram as a triggering signal. The analysis was successfull in 117 of 131 trials. In five pregnancies no successful analysis was obtained. Fetal distress developed in five fetuses of 59 but not perinatal deaths occurred. The sensitivity of the antepartum DI in predicting fetal distress in labor was 80% and the predictive value was 44%. The relative risk for intrapartum fetal distress in labor after a pathologic antepartal DI compared with normal DI was 22, which is highly significant (p less than 0.001).

Interval index: a measure of fetal heart rate accelerations

Interval index (II) is a product of statistical analysis of fetal heart intervals measured from fetal electrocardiography and it describes the long term variability. II and three visual parameters of fetal heart rate (FHR) accelerations: the number of accelerations, the heights of maximal acceleration and the sum of accelerations in 40 five-minute samples of abdominal fetal electrography were compared to find out whether II could be used as an automated objective measure of FHR accelerations (r = 0.85), but the correlation was highly significant also with the maximal acceleration and the number of ac-FHR had a poor correlation with accelerations.