Giant Fetal Magnetocardiogram P Waves in Congenital Atrioventricular Block

Fetal magnetocardiogram waveform characteristics

BACKGROUND

Fetal magnetocardiography (fMCG) is the most direct and precise method of assessing fetal rhythm and conduction. Although the utility of fMCG for evaluation of fetuses with serious arrhythmia is generally acknowledged, many aspects of fetal rhythm and conduction are relatively unstudied.

OBJECTIVE

To record fMCG in a large group of normal fetuses in order to provide a more comprehensive evaluation of fMCG waveform characteristics, including waveform intervals, amplitudes, and morphology.

METHODS

The subjects were 132 healthy women with uncomplicated singleton pregnancies, studied at 15.7-39.9 (mean 28.9) weeks' gestation in 259 sessions. The P, PR, QRS, QT, QTc, and RR intervals and the P/QRS and T/QRS amplitude ratios were measured.

MAIN RESULTS

The P, PR, QRS, and RR intervals increased with gestational age, but QT and QTc did not. U-waves were seen in 11% of fetuses. The T-waves were often flat with low T/QRS amplitude ratios. Equiphasic QRS complexes were associated with tall P-waves. The PR, QRS, and QT intervals showed a power law dependence on RR interval with power law exponents 0.445, 0.363, and 0.381, respectively.

SIGNIFICANCE

The data establish prediction intervals for fMCG waveform intervals and amplitudes in normal fetuses. This is critical for identification of fetuses with abnormal rhythm. Our study is the first to document the incidence of U-waves and flat T-waves in the fetus, both of which are uncommon postnatally. The association of tall P-waves with equiphasic QRS complexes provides a useful means of improving the resolution of fetal P-waves.

Segmented independent component analysis for improved separation of fetal cardiac signals from nonstationary fetal magnetocardiograms

Fetal magnetocardiograms (fMCGs) have been successfully processed with independent component analysis (ICA) to separate the fetal cardiac signals, but ICA effectiveness can be limited by signal nonstationarities due to fetal movements. We propose an ICA-based method to improve the quality of fetal signals separated from fMCG affected by fetal movements. This technique (SegICA) includes a procedure to detect signal nonstationarities, according to which the fMCG recordings are divided in stationary segments that are then processed with ICA. The first and second statistical moments and the signal polarity reversal were used at different threshold levels to detect signal transients. SegICA effectiveness was assessed in two fMCG datasets (with and without fetal movements) by comparing the signal-to-noise ratio (SNR) of the signals extracted with ICA and with SegICA. Results showed that the SNR of fetal signals affected by fetal movements improved with SegICA, whereas the SNR gain was negligible elsewhere. The best measure to detect signal nonstationarities of physiological origin was signal polarity reversal at threshold level 0.9. The first statistical moment also provided good results at threshold level 0.6. SegICA seems a promising method to separate fetal cardiac signals of improved quality from nonstationary fMCG recordings affected by fetal movements.

Clinical course and outcome of antenatally detected atrioventricular block: experience of a single tertiary centre and review of the literature

OBJECTIVE

The objective is to study the course and outcome of fetuses with congenital atrioventricular block (AVB) in a single centre.

METHODS

Retrospective analysis of cases diagnosed prenatally with second and third degree AVB. The clinical characteristics and outcome of fetal AVB were evaluated including in utero treatment.

RESULTS

Sixty-two cases were studied. AVB was associated with a congenital heart defect (CHD-AVB) in 17 cases (27%), whereas it was isolated (i-AVB) in 45 (73%), 42 of which were associated with maternal antibodies. There were nine (52.9%) live births in the CHD-AVB group, five of which (55%) resulted in infant deaths. In the i-AVB group, there were 40/45 (88.9%) live births and 1/40 (2.5%) infant death; 36 (90%) babies required a permanent pacemaker. The only factor predictive of postnatal death was the presence of CHD (5/9 vs 1/39 or 48.7 [3.6; 1457.7], p < 0.001). Nineteen fetuses (40.5%) with i-AVB received steroids in utero. No difference in outcome was found between the AVB treated in utero versus the no-treatment group in terms of permanent pacemaker placement, postnatal death or development of dilated cardiomyopathy.

CONCLUSION

The most important prognostic factor for congenital AVB is the association with CHD. In utero treatment remains questionable.

Electrophysiologic features of fetal ventricular aneurysms and diverticula

OBJECTIVE

Congenital ventricular wall defects are very rare and include congenital ventricular aneurysms (CVAs) and diverticula (CVDs).

METHOD

We report a series of five fetuses: three with CVAs and two with CVDs referred due to fetal arrhythmia. In addition to routine fetal echocardiography, fetal magnetocardiography (fMCG) was used. The literature in CVA and CVD is reviewed.

RESULTS

Incessant premature ventricular contractions (PVC), mainly bigeminy and trigeminy were found in three fetuses with CVAs and in one with CVD, who also had ventricular couplets. The other fetus with CVD, referred because of PVCs, had only sinus tachycardia. ST elevation was noted in two. Fetal movement had a variable impact on PVCs. Postnatal evaluation demonstrated two persistent left ventricular aneurysms and one persistent right CVD; one CVD resolved at 35-week gestation. Two neonates had incessant PVCs. Both arrhythmias resolved spontaneously while being treated with propranolol.

CONCLUSION

FMCG is complementary to echocardiographic imaging. In fetuses with left ventricular wall defects, additional electrophysiological diagnosis can be made by fMCG, including the complexity of ventricular ectopy, arrhythmic response to fetal movement, presence of ST-T wave abnormalities, and atrial amplitude increases. Prenatal risk factor assessment using fMCG can additionally support post-natal treatment and follow-up.

Diagnosis and treatment of fetal arrhythmia

AIMS

Detection and careful stratification of fetal heart rate (FHR) is extremely important in all pregnancies. The most lethal cardiac rhythm disturbances occur during apparently normal pregnancies where FHR and rhythm are regular and within normal or low-normal ranges. These hidden depolarization and repolarization abnormalities, associated with genetic ion channelopathies cannot be detected by echocardiography, and may be responsible for up to 10% of unexplained fetal demise, prompting a need for newer and better fetal diagnostic techniques. Other manifest fetal arrhythmias such as premature beats, tachycardia, and bradycardia are commonly recognized.

METHODS

Heart rhythm diagnosis in obstetrical practice is usually made by M-mode and pulsed Doppler fetal echocardiography, but not all fetal cardiac time intervals are captured by echocardiographic methods.

RESULTS AND CONCLUSIONS

This article reviews different types of fetal arrhythmias, their presentation and treatment strategies, and gives an overview of the present and future diagnostic techniques.

Diagnosis and treatment of fetal cardiac disease: a scientific statement from the American Heart Association

BACKGROUND

The goal of this statement is to review available literature and to put forth a scientific statement on the current practice of fetal cardiac medicine, including the diagnosis and management of fetal cardiovascular disease.

METHODS AND RESULTS

A writing group appointed by the American Heart Association reviewed the available literature pertaining to topics relevant to fetal cardiac medicine, including the diagnosis of congenital heart disease and arrhythmias, assessment of cardiac function and the cardiovascular system, and available treatment options. The American College of Cardiology/American Heart Association classification of recommendations and level of evidence for practice guidelines were applied to the current practice of fetal cardiac medicine. Recommendations relating to the specifics of fetal diagnosis, including the timing of referral for study, indications for referral, and experience suggested for performance and interpretation of studies, are presented. The components of a fetal echocardiogram are described in detail, including descriptions of the assessment of cardiac anatomy, cardiac function, and rhythm. Complementary modalities for fetal cardiac assessment are reviewed, including the use of advanced ultrasound techniques, fetal magnetic resonance imaging, and fetal magnetocardiography and electrocardiography for rhythm assessment. Models for parental counseling and a discussion of parental stress and depression assessments are reviewed. Available fetal therapies, including medical management for arrhythmias or heart failure and closed or open intervention for diseases affecting the cardiovascular system such as twin-twin transfusion syndrome, lung masses, and vascular tumors, are highlighted. Catheter-based intervention strategies to prevent the progression of disease in utero are also discussed. Recommendations for delivery planning strategies for fetuses with congenital heart disease including models based on classification of disease severity and delivery room treatment will be highlighted. Outcome assessment is reviewed to show the benefit of prenatal diagnosis and management as they affect outcome for babies with congenital heart disease.

CONCLUSIONS

Fetal cardiac medicine has evolved considerably over the past 2 decades, predominantly in response to advances in imaging technology and innovations in therapies. The diagnosis of cardiac disease in the fetus is mostly made with ultrasound; however, new technologies, including 3- and 4-dimensional echocardiography, magnetic resonance imaging, and fetal electrocardiography and magnetocardiography, are available. Medical and interventional treatments for select diseases and strategies for delivery room care enable stabilization of high-risk fetuses and contribute to improved outcomes. This statement highlights what is currently known and recommended on the basis of evidence and experience in the rapidly advancing and highly specialized field of fetal cardiac care.

Clinical application of magnetocardiography

Magnetocardiography is a noninvasive contactless method to measure the magnetic field generated by the same ionic currents that create the electrocardiogram. The time course of magnetocardiographic and electrocardiographic signals are similar. However, compared with surface potential recordings, multichannel magnetocardiographic mapping (MMCG) is a faster and contactless method for 3D imaging and localization of cardiac electrophysiologic phenomena with higher spatial and temporal resolution. For more than a decade, MMCG has been mostly confined to magnetically shielded rooms and considered to be at most an interesting matter for research activity. Nevertheless, an increasing number of papers have documented that magnetocardiography can also be useful to improve diagnostic accuracy. Most recently, the development of standardized instrumentations for unshielded MMCG, and its ease of use and reliability even in emergency rooms has triggered a new interest from clinicians for magnetocardiography, leading to several new installations of unshielded systems worldwide. In this review, clinical applications of magnetocardiography are summarized, focusing on major milestones, recent results of multicenter clinical trials and indicators of future developments.

Fetal arrhythmias associated with cardiac rhabdomyomas

BACKGROUND

Primary heart tumors in fetuses are rare and mainly represent rhabdomyomas. The tumors have a variable expression and can be associated with arrhythmias, including both wide and narrow QRS tachycardia. Although multiple Doppler techniques exist to assess fetal heart rhythm, it can be difficult to record precise electrophysiological abnormalities in fetal life.

OBJECTIVE

Investigations defining precise electrophysiological diagnosis were performed by using fetal magnetocardiography (fMCG).

METHODS

In addition to routine fetal echocardiography, fMCG was used to investigate electrophysiological rhythm patterns in a series of 10 fetuses with cardiac rhabdomyomas.

RESULTS

The mean gestational age of the fetuses was 28.6 ± 4.7 weeks. The multiple rhabdomyomas were mainly located in the right and left ventricles as well as around the atrioventricular groove. Arrhythmias or conduction abnormalities were diagnosed in all 10 patients, although only 6 of them were referred due to that indication. Remarkably, 80% (8 of 10) had associated Wolff-Parkinson-White pre-excitation. In addition, we found prominent P waves in 4 fetuses.

CONCLUSION

In fetuses with rhabdomyomas, a disease where rhythm pathology is common, precise electrophysiological diagnosis can now be made by fMCG. fMCG is complimentary to echocardiography for rhythm assessment and can detect conduction abnormalities that are not possible to diagnose prenatally with M-mode or pulsed Doppler ultrasound. Risk factor assessment using fMCG can support pregnancy management and postnatal treatment and follow-up.

Maternal MCG interference cancellation using splined independent component subtraction

Signal distortion is commonly observed when using independent component analysis (ICA) to remove maternal cardiac interference from the fetal magnetocardiogram. This can be seen even in the most conservative case where only the independent components dominated by maternal interference are subtracted from the raw signal, a procedure we refer to as independent component subtraction (ICS). Distortion occurs when the subspaces of the fetal and maternal signals have appreciable overlap. To overcome this problem, we employed splining to remove the fetal signal from the maternal source component. The maternal source components were downsampled and then interpolated to their original sampling rate using a cubic spline. A key aspect of the splining procedure is that the maternal QRS complexes are downsampled much less than the rest of the maternal signal so that they are not distorted, despite their higher bandwidth. The splined maternal source components were projected back onto the magnetic field measurement space and then subtracted from the raw signal. The method was evaluated using data from 24 subjects. We compared the results of conventional, i.e., unsplined, ICS with our method, splined ICS, using matched filtering as a reference. Correlation and subjective assessment of the P-wave and QRS complex were used to assess the performance. Using ICS, we found that the P-wave was adversely affected in 7 of 24 (29%) subjects, all having correlations less than 0.8. Splined ICS showed negligible distortion and improved the signal fidelity to some extent in all subjects. We also demonstrated that maternal T-wave interference could be problematic when the fetal and maternal heartbeats were synchronous. In these instances, splined ICS was more effective than matched filtering.

Fetal cardiac arrhythmia detection and in utero therapy

The human fetal heart develops arrhythmias and conduction disturbances in response to ischemia, inflammation, electrolyte disturbances, altered load states, structural defects, inherited genetic conditions, and many other causes. Yet sinus rhythm is present without altered rate or rhythm in some of the most serious electrophysiological diseases, which makes detection of diseases of the fetal conduction system challenging in the absence of magnetocardiographic or electrocardiographic recording techniques. Life-threatening changes in QRS or QT intervals can be completely unrecognized if heart rate is the only feature to be altered. For many fetal arrhythmias, echocardiography alone can assess important clinical parameters for diagnosis. Appropriate treatment of the fetus requires awareness of arrhythmia characteristics, mechanisms, and potential associations. Criteria to define fetal bradycardia specific to gestational age are now available and may allow detection of ion channelopathies, which are associated with fetal and neonatal bradycardia. Ectopic beats, once thought to be entirely benign, are now recognized to have important pathologic associations. Fetal tachyarrhythmias can now be defined precisely for mechanism-specific therapy and for subsequent monitoring of response. This article reviews the current and future diagnostic techniques and pharmacologic treatments for fetal arrhythmia.

Early Diagnosis and Treatment of Atrioventricular Block in the Fetus Exposed to Maternal Anti-SSA/Ro-SSB/La Antibodies

Background— A fetus exposed to maternal anti-SSA/Ro or anti-SSB/La antibodies (or both) may develop complete atrioventricular block (AVB), which results in high prenatal and postnatal morbidity and mortality. Until recently, only high-grade AVB could be diagnosed in utero. The tissue velocity–based fetal kinetocardiogram (FKCG) enables accurate measurement of AV conduction time and diagnosis of low-grade AVB. In the present multicenter observational study, we used FKCG to detect first-degree AVB in fetuses at risk.

Methods and Results— FKCG was performed in 70 fetuses of 56 mothers who were positive for anti-SSA/Ro and/or anti-SSB/La. Fetuses were monitored with weekly FKCG from 13 to 24 weeks’ gestation, followed by monthly assessments until delivery in unaffected fetuses and weekly assessments in affected fetuses. AV conduction in 70 at-risk and 109 normal fetuses was compared. FKCG was obtained readily in all fetuses; 6 showed first-degree AVB (AV conduction time >2 z scores above normal mean) at 21 to 34 gestational weeks. Immediate maternal treatment with dexamethasone resulted in normalization of AV conduction in all affected fetuses within 3 to 14 days. AV conduction time in the remaining 64 untreated fetuses remained normal throughout gestation. The ECG PR interval immediately after birth was normal in all affected newborns. No child developed AVB or cardiomyopathy in the subsequent 1- to 6-year (median 4-year) follow-up.

Conclusions— The present findings suggest that an FKCG can detect first-degree AVB in the fetus exposed to maternal anti-SSA/Ro or anti-SSB/La antibodies (or both). Dexamethasone given on detection was associated with normalized AV conduction in fetuses with first-degree AVB. No fetus in the present study developed complete prenatal or postnatal AVB.

Overview of fetal arrhythmias

PURPOSE OF REVIEW

Though fetal arrhythmias account for a small proportion of referrals to a fetal cardiologist, they may be associated with significant morbidity and mortality. The present review outlines the current literature with regard to the diagnosis and, in brief, some management strategies in fetal arrhythmias.

RECENT FINDINGS

Advances in echocardiography have resulted in significant improvements in our ability to elucidate the mechanism of arrhythmia at the bedside. At the same time, magnetocardiography is broadening our understanding of mechanisms of arrhythmia especially as it pertains to ventricular arrhythmias and congenital heart block. It provides a unique window to study electrical properties of the fetal heart, unlike what has been available to date. Recent reports of bedside use of fetal ECG make it a promising new technology. Fetal magnetocardiography is also developing. The underlying mechanisms resulting in immune-mediated complete heart block in a small subset of 'at-risk' fetuses is under investigation.

SUMMARY

There have been great strides in noninvasive diagnosis of fetal arrhythmias. However, we still need to improve our knowledge of the electromechanical properties of the fetal heart as well as the mechanisms of arrhythmia to further improve outcomes. Multiinstitutional collaborative studies are needed to help answer some of the questions regarding patient, drug selection and management algorithms.

Space-time database for standardization of adult magnetocardiogram-making standard MCG parameters

BACKGROUND

The magnetocardiogram (MCG) is a promising medical tool for detecting and visualizing abnormal cardiac electrical activation in heart-disease patients. However, there is no large-scale MCG database of healthy subjects, and there is little knowledge of gender- and age-related influences on MCG data.

METHODS AND RESULTS

We obtained MCG data from 869 subjects (554 men, 315 women) using a conventional 64-channel MCG system, which covers the whole heart. Electrocardiogram (ECG) data were also obtained; 464 people (268 men, 196 women) were identified as a normal group using ECG data. Time intervals (PQ, QRS, QT, and QTc), current distributions (maximum current vector (MCV), and the total current vector (TCV)) of MCG data of the 464 normal subjects were analyzed to obtain basic MCG parameters. Although mean values of PQ and QRS intervals of the male subjects were slightly longer than those of the female subjects, no intervals were correlated with gender or age. The correlation between PQ intervals of ECG and those of MCG was better than the correlation between QRS and QT intervals of ECG and those of MCG. Both MCV and TCV angles were much smaller than the electrical-axis angle in ECG. Although TCVs of the QRS and T waves were stable, the women's mean T-wave-TCV angles significantly increased with age. The maximum amplitude of the P wave was about 1.7 pT, and the value of the QRS complex was about 20-25 pT. Moreover, the T-wave amplitude decreases with age.

CONCLUSION

The MCG standard space-time parameters determined here provide a normal range for MCG parameters.

Electrophysiological characteristics of fetal atrioventricular block

OBJECTIVES

The purpose of our work was to define the complex electrophysiological characteristics seen in second- (2 degrees) and third-degree (3 degrees) atrioventricular block (AVB) and to longitudinally follow the development of atrial and ventricular heart rate and rhythm patterns with a goal of identifying heart rate and rhythm patterns associated with urgent delivery or neonatal pacing.

BACKGROUND

The electrophysiological characteristics of congenital AVB before birth have not been extensively studied, yet the mortality from this disease is substantial. Along with advances in fetal therapies and interventions, a comprehensive natural history specific to the etiology of AVB, as well as the electrophysiological factors influencing outcome, are needed to best select treatment options.

METHODS

Twenty-eight fetuses with AVB were evaluated by fetal magnetocardiography; 21 fetuses were evaluated serially.

RESULTS

Fetuses with 2 degrees AVB and isolated 3 degrees AVB showed: 1) diverse atrial rhythms and mechanisms of atrioventricular conduction during 2 degrees AVB; 2) junctional ectopic tachycardia and ventricular tachycardia during 3 degrees AVB; 3) reactive ventricular and atrial fetal heart rate (FHR) tracings at ventricular rates >56 beats/min; and 4) flat ventricular FHR tracings at ventricular rates <56 beats/min despite reactive atrial FHR tracings. In contrast, fetuses with 3 degrees AVB associated with structural cardiac disease exhibited predominantly nonreactive heart rate tracings and simpler rhythms.

CONCLUSIONS

Second-degree AVB, isolated 3 degrees AVB, and 3 degrees AVB associated with structural cardiac disease manifest distinctly different electrophysiological characteristics and outcome. Fetuses with 2 degrees AVB or isolated 3 degrees AVB commonly exhibited complex, changing heart rate and rhythm patterns; all 19 delivered fetuses are alive and healthy. Fetuses with structural cardiac disease and 3 degrees AVB exhibited largely monotonous heart rate and rhythm patterns and poor prognosis. Junctional ectopic tachycardia and/or ventricular tachycardia may be characteristic of an acute stage of heart block.

Performance comparison of six independent components analysis algorithms for fetal signal extraction from real fMCG data

In this study we compare the performance of six independent components analysis (ICA) algorithms on 16 real fetal magnetocardiographic (fMCG) datasets for the application of extracting the fetal cardiac signal. We also compare the extraction results for real data with the results previously obtained for synthetic data. The six ICA algorithms are FastICA, CubICA, JADE, Infomax, MRMI-SIG and TDSEP. The results obtained using real fMCG data indicate that the FastICA method consistently outperforms the others in regard to separation quality and that the performance of an ICA method that uses temporal information suffers in the presence of noise. These two results confirm the previous results obtained using synthetic fMCG data. There were also two notable differences between the studies based on real and synthetic data. The differences are that all six ICA algorithms are independent of gestational age and sensor dimensionality for synthetic data, but depend on gestational age and sensor dimensionality for real data. It is possible to explain these differences by assuming that the number of point sources needed to completely explain the data is larger than the dimensionality used in the ICA extraction.

Prenatal diagnosis of fetal arrhythmias

Life-threatening fetal arrhythmias are rare and warrant sophisticated specialty prenatal care, often provided by maternal-fetal medicine obstetricians, and pediatric and adult cardiologists. This medical field is in quick transition, and new methods of diagnosis and treatment of the fetus with arrhythmias are emerging. In this article, the mechanisms of arrhythmias are presented in light of recent progress in the new field of fetal electrophysiology. Treatments are reviewed with recommendations based on the small number of series of fetal tachycardia and fetal atrioventricular (AV) block drug treatment strategies published to date. Finally, a summary of areas of potential future research is provided.

Optimal filter design for shielded and unshielded ambient noise reduction in fetal magnetocardiography

The greatest impediment to extracting high-quality fetal signals from fetal magnetocardiography (fMCG) is environmental magnetic noise, which may have peak-to-peak intensity comparable to fetal QRS amplitude. Being an unstructured Gaussian signal with large disturbances at specific frequencies, ambient field noise can be reduced with hardware-based approaches and/or with software algorithms that digitally filter magnetocardiographic recordings. At present, no systematic evaluation of filters' performances on shielded and unshielded fMCG is available. We designed high-pass and low-pass Chebychev II-type filters with zero-phase and stable impulse response; the most commonly used band-pass filters were implemented combining high-pass and low-pass filters. The achieved ambient noise reduction in shielded and unshielded recordings was quantified, and the corresponding signal-to-noise ratio (SNR) and signal-to-distortion ratio (SDR) of the retrieved fetal signals was evaluated. The study regarded 66 fMCG datasets at different gestational ages (22-37 weeks). Since the spectral structures of shielded and unshielded magnetic noise were very similar, we concluded that the same filter setting might be applied to both conditions. Band-pass filters (1.0-100 Hz) and (2.0-100 Hz) provided the best combinations of fetal signal detection rates, SNR and SDR; however, the former should be preferred in the case of arrhythmic fetuses, which might present spectral components below 2 Hz.

A method for the automatic reconstruction of fetal cardiac signals from magnetocardiographic recordings

Fetal magnetocardiography (fMCG) allows monitoring the fetal heart function through algorithms able to retrieve the fetal cardiac signal, but no standardized automatic model has become available so far. In this paper, we describe an automatic method that restores the fetal cardiac trace from fMCG recordings by means of a weighted summation of fetal components separated with independent component analysis (ICA) and identified through dedicated algorithms that analyse the frequency content and temporal structure of each source signal. Multichannel fMCG datasets of 66 healthy and 4 arrhythmic fetuses were used to validate the automatic method with respect to a classical procedure requiring the manual classification of fetal components by an expert investigator. ICA was run with input clusters of different dimensions to simulate various MCG systems. Detection rates, true negative and false positive component categorization, QRS amplitude, standard deviation and signal-to-noise ratio of reconstructed fetal signals, and real and per cent QRS differences between paired fetal traces retrieved automatically and manually were calculated to quantify the performances of the automatic method. Its robustness and reliability, particularly evident with the use of large input clusters, might increase the diagnostic role of fMCG during the prenatal period.

Fetal source extraction from magnetocardiographic recordings by dependent component analysis

Fetal magnetocardiography (fMCG) has been extensively reported in the literature as a non-invasive, prenatal technique that can be used to monitor various functions of the fetal heart. However, fMCG signals often have low signal-to-noise ratio (SNR) and are contaminated by strong interference from the mother's magnetocardiogram signal. A promising, efficient tool for extracting signals, even under low SNR conditions, is blind source separation (BSS), or independent component analysis (ICA). Herein we propose an algorithm based on a variation of ICA, where the signal of interest is extracted using a time delay obtained from an autocorrelation analysis. We model the system using autoregression, and identify the signal component of interest from the poles of the autocorrelation function. We show that the method is effective in removing the maternal signal, and is computationally efficient. We also compare our results to more established ICA methods, such as FastICA.

Automatic detection of cardiac waves on fetal magnetocardiographic signals

Fetal magnetocardiography (fMCG) provides fetal cardiac traces useful for the prenatal monitoring of fetal heart function. In this paper, we describe an analytical model (ACWD) for the automatic detection of cardiac waves boundaries that works on fetal signals reconstructed from fMCG by means of independent component analysis. ACWD was validated for 45 healthy and 4 arrhythmic fetuses ranging from 22 to 37 weeks; ACWD outcomes were compared with the estimates of three independent investigators. Descriptive statistics were used to assess correspondence between the outcomes of the automatic and manual approaches. The parametric two-tailed Pearson correlation test (alpha=0.01) was employed to quantify, by means of the coefficients of determination, the amount of common variation between the sequences of intervals quantified automatically and manually. ACWD performances on short and long rhythm strips were investigated. ACWD demonstrated to be a robust tool providing dependable estimates of cardiac intervals and their variability during the third gestational trimester also in case of fetal arrhythmias. SNR and stability of fetal traces were the factors limiting ACWD performances. ACWD computation time, which was approximately 1:600 with respect to the manual procedure, was comparable with the time required for fCTI estimation on averaged beats.