Extracellular potentials related to intracellular action potentials during impulse conduction in anisotropic canine cardiac muscle.

Abstract

This paper considers a quantitative description of intracellular and transmembrane currents in anisotropic muscle, with emphasis on the factors that determine the extracellular potentials. Although Vmax of the intracellular action potential had no relation to changes in conduction velocity in anisotropic tissue with constant membrane properties, the extracellular waveforms were quite sensitive to velocity changes. Large amplitude biphasic deflection occurred in the fast areas, and in the slow areas the waveforms were of lower amplitude and triphasic in shape; i.e., negative potentials preceded the biphasic positive-negative deflection. The extracellular potentials were simulated on the bases of a model of intracellular currents, and the theoretical and measured results showed good agreement. In tissue with anisotropic conductivity, the relationship between the spatial intracellualr potential gradient and the magnitude of the extracellular potential of the excitation wave was opposite to the classical relationship in isotropic tissue. Due to the influence of the effective intracellular conductivity on the spread of intracellular currents and on conduction velocity, in anisotropic tissue the extracellular potential decreased as the intracellular potential gradient increased. The peak values of the positive and negative potentials and the spatial distribution of the potential gradients varied considerably along the activation front. These findings were accounted for by differences in the distribution and spatial extent of the transmembrane currents, which were determined by the intracellular currents. The theoretical analysis showed that intracellular and transmembrane currents were proportional to the local conduction velocities of the wavefront. Thereby, it was not possible to have a "uniform layer" of current when there were differences in conduction velocity along the length of the excitation wave. The implications of the analysis are considerable, since the gratifying agreement between the theoretical and measured results indicates that the details of the extracellular waveforms can be explained on the basis of the distribution of intracellular currents; i.e., extracellular potentials provide a sensitive index of intracellular current flow.

Effect of tissue anisotropy on extracellular potential fields in canine myocardium in situ.

“…We do not know why the wavefront voltages in these studies were lower than in our study. In another in vitro study (Spach et al, 1979), there were effects of tissue anisotropy, but the extracellular voltages were very small. sotropic tissue.…”

“…For example, the extracellular voltage across a depolarization wave in in vitro ventricular trabeculae varies by a factor of three as the direction of propagation is changed (Clcrc, 1976). In superfused myocardium in vitro, the form of the extracellular potential is strongly affected by electrical anisotropy (Spach et al, 1979). In in situ canine ventricle, as well, potential fields around localized depolarization waves are qualitatively dissimilar to those expected on the basis of the assumption of electrical isotropy (Corbin and Scher, 1977;Roberts et al, 1979).…”

“…Although Spach et al (1979) studied electrical anisotropy in a thin layer of muscle in vitro, they did not produce values of electrical conductivity or wavefront strength applicable to the intact heart. Neither did their study include the possibility that extracellular resistivity is anisotropic, although evidence (Clerc, 1976) indicates that both extracellular and intracellular forms of resistivity are anisotropic.…”

Effects of anisotropy on the development of cardiac arrhythmias associated with focal activity

“…Myocyte structure is asymmetrical, with average adult myocytes being 100-150 µm in length and 15-25 µm in width [13,23], with the cellular arrangement of these cells giving the tissue a structural anisotropy. Anisotropy is further enhanced by the spatial distribution of gap junctions -ensembles of intercellular ion channels providing the electrical pathway between neighboring cells-such that the propagation velocity in the transverse direction is lower than that in the longitudinal direction, with ratios of 1 to 2.7 in the ventricle and up to 1 to 12 in the atrial crista terminalis [2,11,19,36].…”

Characteristics of Virtual Unipolar Electrogram Voltage and Characteristics of Isthmus Block during Radiofrequency Ablation of Typical Atrial Flutter

“…18,19) In this study, pacing from the CS before RFA resulted in RS or rS unipolar electrograms in the CTI. After RFA with complete CTI block (group 1), the paced wavefront propagated around the TA to the other side of the ablation line.…”