M-Sign in Middle Cerebral Artery Doppler Waveforms: A Sign of Fetal Vasoconstriction Before and After Open Fetal Spina Bifida Repair

Abstract

Background Increased pulse wave reflection in the fetal arterial system, illustrated by a second systolic peak (M-sign) in middle cerebral artery (MCA) Doppler waveforms, allows interpretation of fetal systemic vasoconstriction. Little is known about fetal vascular regulation during fetal spina bifida (fSB) repair. Therefore, the aim of this study was to analyze MCA-Doppler waveform changes before, during, and after fSB repair. Patients and Methods 31 pregnant women who underwent fSB repair were included. Fetal MCA-Doppler waveforms were prospectively analyzed before, during and after fSB repair, and categorized as follows: normal systolic downslope, systolic shoulder, second systolic peak (M-sign), and concave systolic downslope. These MCA waveforms were related to maternal and fetal characteristics, to anesthetic medication, and to umbilical artery (UA) waveforms. Results Before fSB repair, all fetuses repeatedly presented M-signs. After initiation of desflurane for general anesthesia, systolic shoulder and the M-sign vanished in 24/31 (78%) fetuses and 19/31 (61%) showed transient UA ARED flow. A significant association between these two Doppler findings was found (p=0.007). After fSB repair, signs of increased pulse wave reflection reappeared but resolved over time (23 days ± 20, SD) in all fetuses. Conclusion Both fSB and intrauterine repair influence fetal vascular regulation. This phenomenon can be illustrated by MCA-Doppler waveforms. While anesthetic agents transiently eliminated M-signs and often provoked a UA ARED flow, fSB repair finally led to normalization of MCA-Doppler waveforms indicating return to normal fetal vascular regulation.

Zusammenfassung

Hintergrund Eine erhöhte Pulswellenreflektion im fetalen Kreislauf, im Sinne erhöhter Vasoaktivität, spiegelt sich in einem zweiten systolischen Ausschlag (M-Zeichen) der A. cerebri media (ACM) wider. Bisher ist kaum etwas über die fetale Kreislaufregulation während der fötalen Spina Bifida (fSB) Operation bekannt. Daher war das Ziel dieser Studie, die Änderungen im ACM-Dopplerwellenmuster vor, während und nach fSB-Operationen zu analysieren. Methodik 31 konsekutiv für fSB operierte Feten wurden eingeschlossen. ACM-Doppler wurden prospektiv vor, während und nach der fSB-Operation analysiert und wie folgt kategorisiert: normal, systolische Schulter, M-Zeichen, konkaves Muster. Die Wellenmuster wurden mit maternalen und fetalen Charakteristika sowie mit Narkosemitteln und dem A. umbilicalis-(UA)-Muster korreliert. Resultate Alle Feten zeigten M-Zeichen vor der fSB-Operation. Nach Beginn der Vollnarkose mit Desfluran verschwanden die Zeichen der Vasokonstriktion in 24/31 (78%) – und 19/31 (61%) der Feten zeigten einen Block oder Rückfluss in der UA. Der Zusammenhang zwischen beiden Dopplerbefunden war signifikant (p=0,007). Zeichen erhöhter Pulswellenreflektion sind nach der fSB-Operation initial wieder erschienen, über die Zeit (23 Tage ± 20, SD) jedoch bei allen Feten verschwunden. Schlussfolgerung Die fSB-Läsion und eine fetale Operation beeinflussen den fetalen Kreislauf. Dieses Phänomen lässt sich gut mittels ACM-Doppler illustrieren. Während die Narkosemittel das M-Zeichen passager verschwinden lassen und oft ein pathologisches UA-Muster provozieren, resultiert die fSB-Operation letztlich in einer Normalisierung des ACM-Dopplermusters bzw. des fetalen Kreislaufes.

Keywords

fetal surgery - MCA-Doppler - second systolic peak - M-sign - myelomeningocele repair

Publication History

Received: 24 June 2021

Accepted after revision: 10 December 2021

Article published online:
08 February 2022

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