Feasibility of non-invasive Foetal electrocardiography in a twin pregnancy.

BACKGROUND: Twin pregnancy is associated with increased perinatal mortality. Close foetal monitoring is therefore warranted. Doppler Ultrasound cardiotocography is currently the only available method to monitor both individual foetuses. Unfortunately, the performance measures of this method are poor and erroneous monitoring of the same twin with both transducers may occur, leaving the second twin unmonitored. In this study we aimed to determine the feasibility of monitoring both foetuses simultaneously in twin gestation by means of non-invasive foetal electrocardiography (NI-fECG), using an electrode patch on the maternal abdomen. METHODS: A NI-fECG recording was performed at 25 + 3 weeks of gestation on a multiparous woman pregnant with dichorionic diamniotic twins. An electrode patch consisting of eight adhesive electrodes was applied on the maternal abdomen, yielding six channels of bipolar electrophysiological measurements. The output was digitized and stored for offline processing. The recorded signals were preprocessed by suppression of high-frequency noise, baseline wander, and powerline interference. Secondly, the maternal ECG was subtracted and segmentation into individual ECG complexes was performed. Finally, ensemble averaging of these individual ECG complexes was performed to suppress interferences. RESULTS: Six different recordings were obtained from each of the six recording channels. Depending on the orientation and distance of the fetal heart with respect to each electrode, a distinction could be made between each fetus based on the morphology of the signals. Yielding of the fetal ECGs was performed manually based on the QRS complexes of each fetus. CONCLUSION: NI-fECG with multiple electrodes allows for monitoring of the fetal heart rate and ECG of both individual fetuses in twin pregnancies.

[Electrohysterography. A promising alternative for monitoring contractions]. / Elektrohysterografie. Een veelbelovend alternatief voor weeënregistratie.

Monitoring contractions during labour using the external tocodynamometer can be difficult or even impossible, and using the invasive intrauterine pressure catheter is associated with rare but serious complications. A new non-invasive technique is currently available: electrohysterography (EHG). This technique converts the electrical activity of the uterine muscle into a legible tocogram. The EHG signal has a high correlation with the intra-uterine pressure and provides a more accurate assessment of uterine activity compared to external tocodynamometry. EHG is suitable for women in labour with failure of the external tocodynamometer. In clinical practice EHG also appeared to report a more detailed tocographic waveform, like hypertonia or unorganized electrical uterine activity. However, its signal quality depends on adequate skin preparation and correct positioning of the electrodes on the maternal abdomen. Hence, with electrohysterography as non-invasive alternative for uterine monitoring, choosing between safety and accuracy is no longer necessary.

Fetal heart rate variability during pregnancy, obtained from non-invasive electrocardiogram recordings.

OBJECTIVE: Non-invasive spectral analysis of fetal heart rate variability is a promising new field of fetal monitoring. To validate this method properly, we studied the relationship between gestational age and the influence of fetal rest-activity state on spectral estimates of fetal heart rate variability. DESIGN: Prospective longitudinal study. SETTING: Tertiary care teaching hospital. POPULATION: Forty healthy women with an uneventful singleton pregnancy. METHODS: Non-invasive fetal electrocardiogram measurements via the maternal abdomen were performed at regular intervals between 14 and 40 weeks of gestation and processed to detect beat-to-beat fetal heart rate. Simultaneous ultrasound recordings were performed to assess fetal rest-activity state. MAIN OUTCOME MEASURES: Absolute and normalized power of fetal heart rate variability in the low (0.04-0.15 Hz) and high (0.4-1.5 Hz) frequency band were obtained, using Fourier Transform. RESULTS: 14% of all measurements and 3% of the total amount of abdominal data (330 segments) was usable for spectral analysis. During 21-30 weeks of gestation, a significant increase in absolute low and high frequency power was observed. During the active state near term, absolute and normalized low frequency power were significantly higher and normalized high frequency power was significantly lower compared with the quiet state. CONCLUSIONS: The observed increase in absolute spectral estimates in preterm fetuses was probably due to increased sympathetic and parasympathetic modulation and might be a sign of autonomic development. Further improvements in signal processing are needed before this new method of fetal monitoring can be introduced in clinical practice.

Bayesian approach to patient-tailored vectorcardiography.

For assessment of specific cardiac pathologies, vectorcardiography is generally considered superior with respect to electrocardiography. Existing vectorcardiography methods operate by calculating the vectorcardiogram (VCG) as a fixed linear combination of ECG signals. These methods, with the inverse Dower matrix method the current standard, are therefore not flexible with respect to different body compositions and geometries. Hence, they cannot be applied with accuracy on patients that do not conform to the fixed standard. Typical examples of such patients are obese patients or fetuses. For the latter category, when recording the fetal ECG from the maternal abdomen the distance of the fetal heart with respect to the electrodes is unknown. Consequently, also the signal attenuation/transformation per electrode is not known. In this paper, a Bayesian method is developed that estimates the VCG and, to some extent, also the signal attenuation in multichannel ECG recordings from either the adult 12-lead ECG or the maternal abdomen. This is done by determining for which VCG and signal attenuation the joint probability over both these variables is maximal given the observed ECG signals. The underlying joint probability distribution is determined by assuming the ECG signals to originate from scaled VCG projections and additive noise. With this method, a VCG, tailored to each specific patient, is determined. The method is compared to the inverse Dower matrix method by applying both methods on standard 12-lead ECG recordings and evaluating the performance in predicting ECG signals from the determined VCG. In addition, to model nonstandard patients, the 12-lead ECG signals are randomly scaled and, once more, the performance in predicting ECG signals from the VCG is compared between both methods. Finally, both methods are also compared on fetal ECG signals that are obtained from the maternal abdomen. For patients conforming to the standard, both methods perform similarly, with the developed method performing marginally better. For scaled ECG signals and fetal ECG signals, the developed method significantly outperforms the inverse Dower matrix method.

The reliability of continuous measurement of mixed venous oxygen saturation during exercise in patients with chronic heart failure.

Continuous assessment of mixed venous oxygen saturation (cSvO(2)) during exercise using a fiber optic pulmonary artery catheter can provide valuable information on the physiological determinants of the exercise capacity in patients with chronic heart failure (CHF). Since its accuracy is not well established during exercise, this study evaluated the reliability of a fiber optic pulmonary artery catheter for measuring SvO(2 )during exercise in CHF patients. Ten patients with stable CHF performed steady-state exercise tests at 30 and 80% of the ventilatory threshold and consequently a symptom-limited incremental exercise test. During the tests, SvO(2 )was monitored continuously using a fiber optic pulmonary artery catheter (CCOmbo, Edwards Lifesciences, Irvine, CA, USA) and by oximetric analysis of mixed venous blood samples obtained at rest (n = 26), steady state (n = 17) and peak exercise (n = 8). There was a significant correlation between oximetrically determined SvO(2) and cSvO(2) values (r = 0.97). The bias between both methods was 0.6% with limits of agreement from -8 to 9%. The limits of agreement for SvO(2 )values <30% (n = 16) were slightly wider than for SvO(2) values >30% (n = 35) (from -10 to 12% and from -7 to 8%, respectively). In conclusion, continuous measurement of SvO(2 )during exercise using a fiber optic pulmonary catheter is reliable in patients with CHF, with somewhat less accurate measurements of SvO(2 )below 30%.

Beat-to-beat detection of fetal heart rate: Doppler ultrasound cardiotocography compared to direct ECG cardiotocography in time and frequency domain.

In order to obtain power spectral information on the fetal heart rate in stages of pregnancy earlier than labor an algorithm has been developed to calculate the fetal heart rate on a beat-to-beat basis from Doppler ultrasound cardiotocographic signals. The algorithm was evaluated by comparing the calculated fetal heart rate with the heart rate determined from direct ECG signals measured with a scalp electrode. Heart rates were compared both in time and frequency domain. In the time domain the results achieved by both methods correlate well (correlation coefficient = 0.977 (p < 0.001)), in the frequency domain the results correlate even better (correlation coefficient = 0.991 (p < 0.001)). Based on these findings, it can be concluded that the developed algorithm provides a valuable tool for obtaining power spectral information on the fetal heart rate in stages of pregnancy earlier than labor.