Velocity and directionality of the electrohysterographic signal propagation

Abstract

Objective: The initiation of treatment for women with threatening preterm labor requires effective distinction between true and false labor. The electrohysterogram (EHG) has shown great promise in estimating and classifying uterine activity. However, key issues remain unresolved and no clinically usable method has yet been presented using EHG. Recent studies have focused on the propagation velocity of the EHG signals as a potential discriminator between true and false labor. These studies have estimated the propagation velocity of individual spikes of the EHG signals. We therefore focus on estimating the propagation velocity of the entire EHG burst recorded during a contraction in two dimensions.

Study design: EHG measurements were performed on six women in active labor at term, and a total of 35 contractions were used for the estimation of propagation velocity. The measurements were performed using a 16-channel two-dimensional electrode grid. The estimates were calculated with a maximum-likelihood approach.

Results: The estimated average propagation velocity was 2.18 (±0.68) cm/s. No single preferred direction of propagation was found.

Conclusion: The propagation velocities estimated in this study are similar to those reported in other studies but with a smaller intra- and inter-patient variation. Thus a potential tool has been established for further studies on true and false labor contractions.

Figure 1.Electrode. placement and directional definition.

Placement of the 16 measuring electrodes. The direction of propagation is defined in relation to the angle θ.

Figure 2. EHG recording. Example of a full EHG recorded by a single electrode (a) and a burst corresponding to a contraction event (b).

Figure 3. Estimated velocities.

Mean and standard deviation of the estimated velocities for all patients.

Figure 4. Directional estimates.

Distribution of estimated directions of propagation for each patient. Each contraction burst is marked with an X.

Figure 5. Visualization of the estimated directions of propagation.

Direction of propagation is estimated for each contraction and marked with a circle.

Figure 6. Directional distribution divided into four quadrants.

Proportion of contractions with origin in each of the four quadrants.