Variability analysis of fetal heart rate signals as obtained from abdominal electrocardiographic recordings

The present paper introduces an original method of digital signal processing for an automatic analysis of non-invasive abdominal ECG recordings on pregnant women starting from the 25th week of gestation. The procedure has been implemented on a DEC-VAX 750 digital computer at the Department of Electrical Engineering, Polytechnic of Milano and the signals are recorded at the Department of Obstetrics and Gynecology "L. Mangiagalli", University of Milano, Italy. The experimental results presented in here are still preliminary as only few cases have been considered up to now (about 20) and the goal of the paper is mainly focused on the algorithmic aspects of the whole procedure implemented in the computer and on the approach of heart rate variability (HRV) signal analysis both in the mother and in the fetus. Abdominal ECG lead processing is illustrated starting from the step of maternal (M) and fetal (F) QRS recognitions through linear digital filtering (derivative and low-pass FIR filter, Weber-Cappellini window) and weighted averaging techniques synchronized with maternal QRS's. Figure 1 a shows the original abdominal lead; figure 1 b the filtered signal for MQRS recognitions; figure 2 a the template of maternal cardiac cycle as obtained after the averaging operation synchronized with the instants of MQRS occurrence. The subtraction of the template results in the abdominal lead shown in figure 1 c in which the contribution of MECG is practically entirely reduced even in the case of MQRS and FQRS overlapping.(ABSTRACT TRUNCATED AT 250 WORDS)     

Fetal electrocardiogram obtained with subcutaneous maternal electrodes. A new method

The low voltage of the fetal heart signals and the usual background interference are the main obstacles in obtaining clear fetal electrocardiographic tracings with a high signal-to-noise ratio. By the use of subcutaneous needle electrodes, impulses from the maternal abdominal wall can be short-circuited. Fetal heart potentials with higher amplitude and less background noise are thus recorded. Fetal viability, presentation, multiple pregnancy, and congenital arrhythmias were diagnosed antenatally by means of the fetal ECG with subcutaneous electrodes and were later correlated with the outcome of the pregnancy. More than two hundred tracings were performed with 98 per cent accuracy.     

Spatial filtering of the fetal electrocardiogram

One of the basic problems in the analysis of the rhythm and the shape of the fetal ECG (FECG) is the interference caused by the electrical activity of the maternal heart (MECG). Methods devised for suppressing the maternal signals in the abdominally recorded leads obviously have to rely on differences in the characteristics of both kinds of signals. In the past various differences have been employed for this purpose such as differences in wave shape, frequency content and source location. The method presented here is based on the latter principle. The electrical sources of the fetal and maternal heart are clearly separated in space. By employing multiple abdominal leads, a linear combination of the recorded signals can be formed which acts effectively as a spatial filter. As such the filtering characteristics depend exclusively on the separation inside the human body (the electrical volume conductor) and, as such, can be expected to be independent of the temporal aspects of the recorded signals. In particular, the obtained filter is unaffected by the occurrence of ectopic beats in either the fetal or the maternal heart. The determination of the required filter (weighting coefficients) is carried out by using the technique of singular value decomposition (SVD) of the data matrix representing the sampled input signals. The filter effectively suppresses the maternal component in the filter output and optimizes the fetal component. The properties of this filter are demonstrated.     

Multi-channel magnetocardiography for detecting beat morphology variations in fetal arrhythmias

OBJECTIVE: Over the last few years, a number of studies have shown that fetal magnetocardiography (fMCG) is useful in describing fetal cardiac activity. A 55-channel MCG system in Ulm was used to record fetal cardiac activity in 12 pregnant women (with normal fetal heart activity in echocardiography) and in 5 pregnant women in whom the echocardiography showed fetal arrhythmias. METHOD: The recorded MCG data were treated in order to eliminate the maternal signal and three MCG channels with the best signals were used to emulate a standard electrocardiogram (ECG) recording so that standard MCG analysis could be performed. RESULTS: The results in assessing fetal electrophysiology, demonstrating its potential, are presented here for two fetuses with recorded supraventricular extrasystoles (SVES) and for one with ventricular extrasystoles (VES). Concerning the SVES, the analysis software OMEGA was able to separate three different beat morphologies. The VES could be detected exactly and have been confirmed by postnatal ECG. CONCLUSION: The beat morphology and the beat-to-beat variations allow new insights into the electrophysiology of the fetal heart.     

An adaptive on-line method for the extraction of the complete fetal electrocardiogram from cutaneous multilead recordings

The detection of a fetal electrocardiogram (FECG) is described to be a so-called inverse problem. A geometric interpretation of such a problem is presented. It can be solved by determining the weights to be used in one or more weighted sums of measurement signals. A novel method is presented to determine these weights. Theoretical and experimental evidence is given that this method has the following attractive properties. Application of the method results in one or more FECG signals, free of maternal ECG (MECG) which are at the same time maximal with respect to noise. It is shown that one FECG signal does not always suffice to describe the observed electrical heart activity in a set of cutaneous electrodes, equivalently to the adult ECG (see figure 7). It is explained and experimentally verified that the application of three thoracic signals is useful to guarantee the suppression of the MECG. The positions of the abdominal electrodes then determine the obtained FECG to noise ratio, and will have no influence on the degree of MECG suppression (see figure 6). It is expected that a total of about eight measurement signals are sufficient in most cases. The method is simple to apply by medical personnel, and after a transient of about 1 s the signals with the mentioned properties are obtained (see figure 5). Further on, the weights are allowed to change in order to adapt automatically to sudden changes in the measurement signal properties (see figure 6). These may occur e. g. due to fetal movement. Application of the method requires no human interpretation or decision in order to obtain the claimed properties.     

超声诊断胎儿心脏横纹肌瘤及其与结节性硬化症的关系

目的　探讨超声诊断胎儿心脏横纹肌瘤的可行性及胎儿心脏横纹肌瘤与家族性结节性硬化症的关系。　方法　使用高频率超声仪 ,以胎儿心尖四腔观为主要切面 ,观察胎儿心脏横纹肌瘤的发生部位 ,肿瘤的数目 ,肿瘤是否导致左、右心室流出道受阻。并对胎儿母亲做腹部超声检查。　结果　在做常规产前超声检查时 ,发现胎儿心脏横纹肌瘤 5例 ,均经病理结果证实 ,其中 1例确切地与结节性硬化症相关联。　结论　胎儿心脏横纹肌瘤与结节性硬化症相关联。胎儿心脏横纹肌瘤常因心衰而死亡 ,又因结节性硬化症的神经系统病变预后极差 ,因此产前超声发现胎儿心脏横纹肌瘤要考虑患有结节性硬化症的可能性 ,同时应对母亲进行相关检查 ,以了解其有无结节性硬化症 ,这对于降低围产期死亡率有非常重要的意义     

Fetal magnetocardiography (fMCG): moving forward in the establishment of clinical reference data by advanced biomagnetic instrumentation and analysis

Cardiotocography and echocardiography are currently standard for fetal heart monitoring. However, both do not provide adequate temporal resolution to measure fetal cardiac time intervals and detect arrhythmias, which can occur during normal sinus rhythm. Fetal magnetocardiography (fMCG) is a non-invasive technique measuring magnetic signals generated by fetal heart activity. Most fMCG devices are installed in research institutions limiting the implementation of this method in a clinical setting. Several institutions made a step forward by installing devices, in particular for fetal investigations, in hospital sites to evaluate the clinical benefit. Based on instrumentation differences which can affect signal quality, there is still no established reference database for fetal cardiac time intervals. A new magnetograph dedicated to fetal recordings was implemented with improved patient comfort. The setting was optimized to establish a standard. A total of 103 healthy fetuses starting as early as possible after the first trimester were recorded and fMCG values of cardiac time intervals were compared to former studies. Data allowed high and reliable detection for all fMCG components starting at 17 weeks. The data were comparable to fMCG multicenter studies, fetal electrocardiography and neonatal ECG results and could serve as a database of norm values for further investigation of fetal arrhythmias.     

Review: Placenta,evolution and lifelong health

The intrauterine environment has an important influence on lifelong health, and babies who grew poorly in the womb are more likely to develop chronic diseases in later life. Placental function is a major determinant of fetal growth and is therefore also a key influence on lifelong health. The capacity of the placenta to transport nutrients to the fetus and regulate fetal growth is determined by both maternal and fetal signals. The way in which the placenta responds to these signals will have been subject to evolutionary selective pressures. The responses selected are those which increase Darwinian fitness, i.e. reproductive success. This review asks whether in addition to responding to short-term signals, such as a rise in maternal nutrient levels, the placenta also responds to longer-term signals representing the mother’s phenotype as a measure of environmental influences across her life course. Understanding how the placenta responds to maternal signals is therefore not only important for promoting optimal fetal growth but can also give insights into how human evolution affected developmental history with long-term effects on health and disease.     

Non-invasive intrapartum fetal ECG: preliminary report

OBJECTIVES: To obtain fetal heart rate, detailed fetal electrocardiography (fECG) signals and uterine contractions during labour using a single device. DESIGN: Prospective observational study. SETTING: Delivery suite at a tertiary referral hospital, London, UK. POPULATION: Fifteen patients at median gestation of 39 weeks (range 24-41) were recruited at median cervical dilatation of 4.0 cm (range 0-10) of whom 8/15 (53%) had intact amniotic membranes. METHODS: Using 12 abdominally sited electrodes, we recorded the composite abdominal signal in pregnancies intrapartum. The recorded data were analysed off-line using a blind signal separation technique. MAIN OUTCOME MEASURES: Success of signal separation and fECG time intervals. RESULTS: Successful fECG signal acquisition was achieved in 12/15 (80%) patients and an averaged fECG waveform acquired. In these patients, P and QRS waves were seen in all cases, and T waves in 11/12 (92%). True beat-to-beat heart rate (HR) was displayed and measures of its variability obtained. The mother's ECG and uterine electrical activity, shown to match tocographically recorded uterine contractions, were also separated and displayed. Failure to acquire fECG in three cases was attributed to excessive abdominal muscular activity and electrical interference. CONCLUSIONS: This study demonstrates a non-invasive technique that displays detailed intrapartum fECG waveforms, HR variability, maternal ECG and uterine contractions simultaneously, all in a single device and which avoids the potential risks of invasive monitoring with a fetal scalp electrode.     

The potential distribution generated by the fetal heart at the maternal abdomen

The pathways along which the electrical currents generated by the fetal heart are conducted to the surface of the maternal abdomen are not known. As a consequence, in recording the fetal electrocardiogram (FECG) it is hard to predict where electrodes should be placed in order to obtain an optimal signal. The amplitude of the FECG varies with gestation, and there is a large interindividual variability in the amplitude of the FECG and in the optimal recording site among subjects within the same gestational age. Attempts have been made to explain these phenomena in terms of volume conduction. In this research the complete potential distribution on the maternal abdomen is studied in connection with the geometrical configuration of the electrical source (fetal heart) and the volume conductor (surrounding tissues). For a small group of pregnant women the abdominal FECG is recorded simultaneously in 32 leads during a period of about one minute, once every two weeks from 20 weeks of gestation onwards. A spatial filtering technique which combines information of all 32 leads is used to provide a trigger of the fetal QRS complexes. Using this trigger, an average fetal complex is constructed for each lead by time coherent averaging, after subtraction of the maternal contribution. These average fetal complexes are combined to plot the complete potential distribution generated by the fetal heart at the maternal abdomen (fetal body surface map, FBSM) at any given time instant during the fetal cardiac cycle. At these recording sessions the geometry is carefully quantified by making transverse scans every 2 cm with a compound echo scanner. The contours of fetal head and body, the placenta and the uterus are manually drawn on hardcopies of the video display images. Real time echoscopy is used to support the identification of the geometry. The contours are fed into a computer using a graphics tablet. The three dimensional surfaces of fetus, placenta and uterus are separately represented by a triangulation of the respective contour lines. Figures 5 and 6 show an example of the triangulated representation of the recorded geometry. Figure 7 shows the average fetal complexes of an individual at 26 weeks of gestation, plotted at the site where they have been recorded.(ABSTRACT TRUNCATED AT 400 WORDS)     

Studies on the measurement of fetal breathing movement by the impedance method (author's transl)

Fetal breathing movements (FBM) were detected without any invasion by recordings of impedance (IMP) variance on the maternal abdominal wall, where the FBM were visible through the myometrium and maternal abdominal wall. FBM was clearly shown by the IMP method in some modification. This IMP recordings consisted in several elements of maternal respiration and pulsation, fetal movements, FBM, etc. FBM elements on IMP recordings appeared to be in clear spike waves and these were identified as the FBM. Considering of the result of fetal respirotachogram utilizing of IMP recordings, FBM did not seemed to be regular movements. Fetal "hiccup' movements were shown as large biphasic spike waves on IMP recordings. FBM were accurately recognized by the separation of the FBM elements from FBM-IMP recordings by utilizing of the analogical subtractive amplifier system. FBM-IMP signals from the data recorder was dealt with the fast Fourier transformation (FFT) utilizing by the mini-computer system and frequency analysis of them was carried out. From the results of FFT passing through the infinite impulse response digital band-pass filter system, the only FBM elements were separately obtained.     

Measurement of the fetal heart rate during pregnancy by a new electrocardiographic technique

An external technique for recording the fetal heart rate (FHR) during pregnancy is described. The system is based upon the detection of the fetal electrocardiogram (ECG) from the maternal abdomen and elimination of the maternal QRS complexes by a new system of subtraction. Fetal QRS complexes with an amplitude of 10 microvolts or more were processed to produce heart rate recordings of much higher quality than previously obtained with the phonocardiographic and ultrasonic systems. The proportion of successful recordings was reduced between 27 and 34 weeks of gestation due to the decrease in size of the fetal QRS complex which occurred at this time; this was a major drawback of the ECG system.     

Misinterpretation of fetal heart rate monitoring in case of intrauterine death

Electronic fetal heart rate monitoring has become a routine examination to assess fetal well-being. This report presents an unusual case in which maternal heart rate tachycardia was obtained from a dead fetus and was interpreted erroneously. The dead fetus conducted maternal ECG even through a scalp electrode by amplifying the input signal through the Automatic Control system of the monitoring equipment. The importance of concomitant maternal radial pulse recording or a real time scan is stressed.     

Fetal and maternal heart rate confusion during intra-partum monitoring: comparison of trans-abdominal fetal electrocardiogram and Doppler telemetry

Objective: To compare intra-partum performance of trans-abdominal electrocardiogram with Doppler telemetry. Methods: In this prospective longitudinal study, simultaneous monitoring with trans-abdominal ECG and Doppler telemetry was performed in 41 uncomplicated term singleton pregnancies during labour. Results: The overall success rate for FHR monitoring was similar between trans-abdominal ECG and Doppler telemetry (88.5?±?16.7% vs 89.4?±?7.6%), except for the second stage of labour. A significantly higher rate of confusion (p?<?0.001) between fetal and maternal heart was found for Doppler telemetry (4.5?±?4.5%) compared with trans-abdominal ECG (1.3?±?1.9%), especially in the second stage and during maternal movements. Conclusions: Trans-abdominal ECG monitoring is feasible, with comparable success rate to traditional Doppler telemetry, without interfering with maternal mobility or requiring midwife intervention. The reduction in maternal\fetal heart rate confusion from trans-abdominal ECG could reduce incorrect obstetric interpretation.     

Transient non-autoimmune fetal heart block

OBJECTIVES: Fetal heart block is a rare and irreversible condition associated with structural heart defects or maternal autoantibodies (SS-A/Ro and SS-B/La) resulting in permanent damage of the atrioventricular (AV) node. This is the first report of 4 cases with a transient fetal heart block in structurally normal hearts without maternal autoantibodies. METHODS: A report on 4 patients seen within a 14-year period at one center with fetal heart block without intracardiac abnormalities or maternal autoantibodies. RESULTS: Three patients were referred to our center with a fetal bradycardia (heart rate 70-85 bpm), between 20 and 33 weeks' gestational age, and 1 for a 'triple' test at 16 weeks' gestational age. Echocardiography showed a complete heart block in 2 fetuses, and a second-degree AV block in the other 2. Heart block had completely resolved at all following visits. Postnatal ECG recordings showed normal sinus rhythm in all patients. Echocardiographic evaluation at presentation and follow-up showed normal cardiac anatomy, without signs of hydrops or cardiac decompensation in all patients. All mothers tested negative on SS-A/Ro and SS-B/La autoantibodies. CONCLUSIONS: Fetal heart block can occur in the absence of structural heart defects and maternal autoantibodies to SS-A/Ro and SS-B/La. The origin of such heart block is unknown, but its course seems benign: none of the patients ever showed ventricular heart rates <55 bpm, signs of congestive heart failure or fetal hydrops. Heart block resolved spontaneously in all patients.     

Antidepressant use during pregnancy: the benefit-risk ratio

Antidepressants are used commonly in pregnancy. Physicians who provide health care for pregnant women with depression must balance maternal well-being with potential fetal risks of these medications. Over the last decade, scores of original and review articles have discussed whether selective serotonin reuptake inhibitors-selective serotonin norepinephrine reuptake inhibitors possess risks to the fetus; however, very little has been done to integrate these potential risks, if they exist, into an overall context of a benefit:risk ratio. This review aims at presenting an updated analysis of fetal and maternal exposure to selective serotonin or norepinephrine reuptake inhibitors to allow an evidence-based benefit:risk ratio. When a psychiatric condition necessitates pharmacotherapy, the benefits of such therapy far outweigh the potential minimal risks of cardiac malformations, primary pulmonary hypertension of the newborn infant, or poor neonatal adaptation syndrome.     

Neonatal death following injuries in utero, in the absence of maternal lesions

The authors report a case of neonatal death at 24 hours following maternal trauma during a traffic accident. The abdominal trauma did not result in any maternal injury. Caesarean delivery was justified by fetal rhythm disorders. A wide variety of fetal injuries, in the absence of maternal injuries, are reported in the literature. Some benefit from an early diagnosis, improving therefore the fetal prognosis.     

Maternal-fetal electrocardiogram conduction with intrapartum fetal death

All parturient patients with fetuses at risk should be simultaneously monitored for relationships of amplitude, duration, and frequency of uterine contractions, and changes in fetal heart rate patterns. Inability to auscultate the fetal heart sounds during labor, in addition to the subjective complaint of the mother of absent fetal movement, should alert the physician to a fetal death despite the display of an electrocardiogram on the oscilloscope and a fetal heart rate record on the paper print-out. Two cases where the maternal electrocardiogram (ECG) was transmitted through a dead fetus to the fetal ECG electrode are presented and discussed.     

Concurrent maternal and fetal ovarian cysts

Due to improvements in ultrasonography, the detection of fetal abdominal masses has increased. We describe a case of co-existing maternal and fetal ovarian cysts in a 37-year-old primiparous woman. The fetal ovarian cyst was first identified in the third trimester and reached a maximum diameter of 9?cm. The maternal cysts were present from 20 weeks onwards; with a maximum diameter of 8?cm. Histological examination showed the maternal lesions were benign dermoid cysts. The fetal lesion resolved spontaneously by 5 months. This case illustrates that fetal and maternal ovarian cysts may co-exist and could potentially have a similar hormonal etiology.     

Assessing cardiac and neurological maturation during the intrauterine period

The world's first magnetoencephalography (MEG) system specifically designed for fetal and newborn assessment has been installed at the University of Arkansas for Medical Sciences. This noninvasive system called SARA (SQUID Array for Reproductive Assessment) consists of 151 primary superconducting sensors that detect biomagnetic fields from the human body. Since the installation of SARA, significant progress has been made toward the ultimate goal of developing a clinical neurological assessment tool for the developing fetus. Using appropriate analysis techniques, cardiac and brain signals are recorded and studied to gain new understanding of fetal maturation. It is clear from our investigations that a combination of assessment protocols including both fetal heart and brain activity is necessary for the development of a comprehensive new method of fetal neurological testing. We plan to implement such a test protocol for fetuses at high risk for neurological impairment due to certain maternal risk factors and/or fetal diagnostic findings.