(1225) Uterine Electrical Activity in Labor: EMMI Insights on Contraction “Pacemakers”

This study aims to analyze the correlation between initiation and duration of Electromyometrial Imaging (EMMI)-reconstructed electrical activity across the whole 3D uterine surface, which could provide new insights into electrophysiological “pacemakers” in human labor contractions.

Study Design: The Washington Institutional Review Board approved this prospective cohort study. Following informed consent, 38 subjects underwent MRI at ~37 weeks of gestation to capture subject-specific body-uterus geometry. Upon admission to Labor & Delivery Unit and during active labor (≥4 cm dilation with regular contractions), ≤192 electrodes were applied to the abdomen and back. Electrical potentials on the body were recorded for ~1 hour. EMMI generated uterine potential maps, electrogram bursts, and isochrone maps of burst initiation and duration (Fig. 1). Four representative uterine EMG (A-D) are shown.

Results: A strong negative correlation (Fig. 2) was observed between burst initiation time and duration, suggesting uterine regions with earlier activation had longer burst durations. Uterine locations B-D in Fig. 1 are depicted in the scatter plot. Statistics of R2, P-values, and slopes for 482 contractions from 38 subjects are also shown in Fig. 2. This finding aligns with the concept that the uterus does not have a single, dedicated, anatomical pacemaker, but instead shows variable initiation sites for each contraction, supporting the idea of multiple, widely dispersed, functional “pacemakers”.

Conclusion: The inverse relationship between burst initiation time and duration highlights the importance of early-activating regions in maintaining normal uterine contractions. These findings challenge the traditional notion of an anatomically fixed uterine pacemaker like the heart's sinoatrial node. Instead, the data support the hypothesis that the uterus operates with multiple functional “pacemakers,” likely coordinated through intrauterine pressure. Future studies should address potential bias from varying detected contractions per subject to refine these findings and explore uterine contraction coordination mechanisms.