Propagation of electrical activity in uterine muscle during pregnancy: a review

Abstract

The uterine muscle (the myometrium) plays its most evident role during pregnancy, when quiescence is required for adequate nourishment and development of the foetus, and during labour, when forceful contractions are needed to expel the foetus and the other products of conception. The myometrium is composed of smooth muscle cells. Contraction is initiated by the spontaneous generation of electrical activity at the cell level in the form of action potentials. The mechanisms underlying uterine quiescence during pregnancy and electrical activation during labour remain largely unknown; as a consequence, the clinical management of preterm contractions during pregnancy and inefficient uterine contractility during labour remains suboptimal. In an effort to improve clinical management of uterine contractions, research has focused on understanding the propagation properties of the electrical activity of the uterus. Different perspectives have been undertaken, from animal and in vitro experiments up to clinical studies and dedicated methods for non‐invasive parameter estimation. A comparison of the results is not straightforward due to the wide range of different approaches reported in the literature. However, previous studies unanimously reveal a unique complexity as compared to other organs in the pattern of uterine electrical activity propagation, which necessarily needs to be taken into consideration for future studies to be conclusive. The aim of this review is to structure current variegated knowledge on the properties of the uterus in terms of pacemaker position, pattern, direction and speed of the electrical activity during pregnancy and labour.

The location of pacemakers in the uteri of pregnant guinea pigs and rats

“…The search for the site and behavior of the pacemaker in the pregnant uterus has a long history (18,30,42). Several authors have suggested that the fundus of the uterus was the main origin of these contractions (2,3,8).…”

Mechanotransduction mechanisms for coordinating uterine contractions in human labor

“…However, there is a significant doubt that myometrial action potentials travel in straight paths. In sheep (Parkington et al 1988), rodent ( Lammers et al 2008), and human (Mikkelsen et al 2013, Rabotti & Mischi 2015 action potentials are not found to travel linearly. The highest resolution electrical mapping of myometrium is in the guinea pig, which reveals that action potentials diverge and loop through tortuous paths, self-terminate, and usually do not propagate more than a few centimeters (Lammers et al 2008) (Fig.…”

“…Assuming the starting point is on the front wall, travel to the back wall is a distance of about 40 cm. Thus, speeds greater than 2 cm/s would be sufficient to accomplish this, and these values are routinely observed in human (Rabotti et al 2010, Rabotti & Mischi 2015 and rodent (Lammers 2013). However, there is a significant doubt that myometrial action potentials travel in straight paths.…”

“…1). In their recent review, Rabotti and Mischi (2015) concluded that electrical propagation in human is unpredictable and demonstrates complex patterns.…”

“…Fundamental physiological questions remain unanswered (Rabotti & Mischi 2015), including the number of pacemakers the In the heart-like model, the uterus has one electrogenic pacemaker at a fixed location, although data have consistently refuted this assumption. Caldeyro-Barcia's data demonstrated that there are at least two pacemakers located on each side of the fundus (Caldeyro-Barcia & Poseiro 1959).…”