by Dr Jay Lu

In this blog post, we’d like to discuss conduction dispersion, a critical parameter in cardiac electrophysiology. Conduction dispersion refers variations in the time it takes for an action potential to travel through the heart muscle. More specifically, it is a measure of the inhomogeneity of conduction velocity throughout the heart. In homogenous tissues, conduction dispersion is low, while in tissues with inhomogeneity in conduction, the dispersion is high.

Why is this important?

There is increasing evidence that clinical arrhythmias are highly associated with cardiac conduction disturbances (1). Electrical uncoupling (disconnection) of cardiac muscle interconnections and inhomogeneity in conduction have been observed in the atria of elderly people (2). Also, functional or structural myocardial inhomogeneities is linked to the vulnerability to ventricular tachycardia and fibrillation (3).

In addition, phase maps of premature beats showed that an increase in inhomogeneity correlated with the propagation of premature impulses and, hence, the induction of reentrant arrhythmias (1). In reentry, the action potential propagates in a circus-like closed loop manner. The phase map during reentry can clearly identify and show that the location and length of the central arc of the functional block (1).

How is conduction dispersion calculated?

It is quantified by the maximal difference in activation times (measured either by electrical mapping with multi-electrode array or optical mapping) between different recording sites. The maximal local phase differences are then plotted spatially in a phase map, showing the spatial distribution of inhomogeneities in conduction and from each map a total homogeneity index is calculated.

In conclusion, quantification of cardiac conduction inhomogeneities is a useful tool (Fig.1) to assess the vulnerability of the myocardial substrate to reentrant arrhythmias. Also, conduction dispersion offers visualization and characterization of local conduction inhomogeneities by phase mapping offers the possibility to detect areas of initial conduction block and potential sites for reentry (Fig.1).

Fig.1 OMapScope provides users with one-click conduction dispersion analysis from optical mapping data. Red arrow indicates the calculated dispersion function.

Reference

1. Lammers, W J et al. “Quantification of spatial inhomogeneity in conduction and initiation of reentrant atrial arrhythmias.” The American journal of physiology vol. 259,4 Pt 2 (1990): H1254-63.
2. Spach, M S, and P C Dolber. “Relating extracellular potentials and their derivatives to anisotropic propagation at a microscopic level in human cardiac muscle. Evidence for electrical uncoupling of side-to-side fiber connections with increasing age.” Circulation research vol. 58,3 (1986): 356-71.
3. Dillon, S M et al. “Influences of anisotropic tissue structure on reentrant circuits in the epicardial border zone of subacute canine infarcts.” Circulation research vol. 63,1 (1988): 182-206. doi:10.1161/01.res.63.1.182