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      Low‐Cost Fetal Magnetocardiography: A Comparison of Superconducting Quantum Interference Device and Optically Pumped Magnetometers

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          Fetal magnetocardiography ( fMCG) is a highly effective technique for evaluation of fetuses with life‐threatening arrhythmia, but its dissemination has been constrained by the high cost and complexity of Superconducting Quantum Interference Device (SQUID) instrumentation. Optically pumped magnetometers ( OPMs) are a promising new technology that can replace SQUIDs for many applications. This study compares the performance of an fMCG system, utilizing OPMs operating in a person‐sized magnetic shield, to that of a conventional fMCG system, utilizing SQUID magnetometers operating in a magnetically shielded room.

          Methods and Results

          fMCG recordings were made in 24 subjects using the SQUID system with the mother lying supine in a magnetically shielded room and the OPM system with the mother lying prone in a person‐sized, cylindrical shield. Signal‐to‐noise ratios of the OPM and SQUID recordings were not statistically different and were adequate for diagnostic purposes with both technologies. Although the environmental noise was higher using the small open‐ended shield, this was offset by the higher signal amplitude achieved with prone positioning, which reduced the distance between the fetus and sensors and improved patient comfort. In several subjects, fMCG provided a differential diagnosis that was more precise and/or definitive than was possible with echocardiography alone.


          The OPM‐based system was portable, improved patient comfort, and performed as well as the SQUID‐based system at a small fraction of the cost. Electrophysiological assessment of fetal rhythm is now practical and will have a major impact on management of fetuses with long QT syndrome and other life‐threatening arrhythmias.

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          Most cited references 11

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          A concordance correlation coefficient to evaluate reproducibility.

           Aigu L. Lin (1989)
          A new reproducibility index is developed and studied. This index is the correlation between the two readings that fall on the 45 degree line through the origin. It is simple to use and possesses desirable properties. The statistical properties of this estimate can be satisfactorily evaluated using an inverse hyperbolic tangent transformation. A Monte Carlo experiment with 5,000 runs was performed to confirm the estimate's validity. An application using actual data is given.
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            Use of P wave configuration during atrial tachycardia to predict site of origin.

            This study sought to construct an algorithm to differentiate left atrial from right atrial tachycardia foci on the basis of surface electrocardiograms (ECGs). Atrial tachycardia is an uncommon form of supraventricular tachycardia, often resistant to drug therapy. A total of 31 consecutive patients with atrial tachycardia due to either abnormal automaticity or triggered rhythm underwent detailed atrial endocardial mapping and successful radiofrequency catheter ablation of a single atrial focus. P wave configuration was analyzed from 12-lead ECGs during tachycardia during either spontaneous or pharmacologically induced atrioventricular block. P waves inscribed above the isoelectric line (TP interval) were classified as positive, below as negative, above and below (or conversely, below and above) as biphasic and flat P waves as isoelectric (0). In 17 patients the tachycardia was located in the right atrium: crista terminalis (n = 4); right atrial appendage (n = 4); lateral wall (n = 4); posteroinferior right atrium (n = 3); tricuspid annulus (n = 1); and near the coronary sinus (n = 1). In 14 patients, atrial tachycardia was located in the left atrium: at the entrance of the right (n = 6) or left (n = 4) superior pulmonary veins; left inferior pulmonary vein (n = 1); inferior left atrium (n = 1); base of left atrial appendage (n = 1); and high lateral left atrium (n = 1). There were no differences in P wave vectors between sites at the right atrial lateral wall versus the right atrial appendage or between sites at the entrance of right versus left superior pulmonary veins. However, analysis of P wave configuration showed that leads aVL and V1 were most helpful in distinguishing right atrial from left atrial foci. The sensitivity and specificity of using a positive or biphasic P wave in lead aVL to predict a right atrial focus was 88% and 79%, respectively. The sensitivity and specificity of a positive P wave in lead V1 in predicting a left atrial focus was 93% and 88%, respectively. 1) Analyses of surface P wave configuration proved to be reasonably good in differentiating right atrial from left atrial tachycardia foci. 2) Leads II, III and aVF were helpful in providing clues for differentiating superior from inferior foci.
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              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.

                Author and article information

                J Am Heart Assoc
                J Am Heart Assoc
                Journal of the American Heart Association: Cardiovascular and Cerebrovascular Disease
                John Wiley and Sons Inc. (Hoboken )
                09 August 2019
                20 August 2019
                : 8
                : 16 ( doiID: 10.1002/jah3.2019.8.issue-16 )
                [ 1 ] Department of Medical Physics University of Wisconsin Madison WI
                [ 2 ] Division of Cardiology Department of Pediatrics Children's Hospital of Wisconsin‐ Milwaukee Milwaukee WI
                [ 3 ] QuSpin, Inc. Louisville CO
                [ 4 ] Department of Physics FFCLRP Ribeirao Preto, University of Sao Paulo Brazil
                Author notes
                [* ] Correspondence to: Ronald T. Wakai, PhD, Department of Medical Physics, Wisconsin Institutes for Medical Research, 1111 Highland Ave, Madison, WI 53705‐2275. E‐mail: rtwakai@
                © 2019 The Authors and QuSpin, Inc. Published on behalf of the American Heart Association, Inc., by Wiley.

                This is an open access article under the terms of the License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

                Page count
                Figures: 5, Tables: 1, Pages: 10, Words: 6177
                Funded by: National Institutes of Health
                Award ID: R21 EB025901
                Award ID: R01 HL63174
                Award ID: R44 HL114182
                Funded by: Small Business Innovative Research
                Award ID: R44 HL114182
                Original Research
                Original Research
                Pediatric Cardiology
                Custom metadata
                20 August 2019
                Converter:WILEY_ML3GV2_TO_NLMPMC version:5.6.7 mode:remove_FC converted:20.08.2019


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