Electrical Potential Distribution Surrounding the Atria during Depolarization and Repolarization in the Dog

SUMMARY. We examined the onset of atrial epicardial excitation by recording unipolar potentials from 360 electrodes arranged in templates affixed to the superior vena cava and right atrium in dogs. Both activation sequence and potential distribution maps were obtained for the period of impulse origin beginning before the surface P wave and continuing through the first 15-20 msec of atrial depolarization. The activation maps demonstrated impulse origin from multiple widely separated sites, resulting in two to three individual wavefronts that merged to form a single widely disseminated wavefront spread over a 50 x 20 mm area by 10-15 msec. Atrial potential maps obtained for the same time periods revealed multiple sites of primary negativity corresponding to the points of impulse origin in the activation maps. The potential distributions and evolution of these maps also indicated the presence of multiple wavefronts originating from widely separated locations, and suggested an extensively dispersed source of impulse origin. One of these sites at the superior cavo-appendicular junction corresponded to the rostral portion of the sinus node and the site of classical unifocal origin. Additional sites of impulse origin and primary negativity distant to the sinus node were noted either concurrently in the same map or in other maps associated with different patterns of impulse initiation. Classical physiological and pharmacological interventions were used to alter adrenergjc and cholinergic input to the atrium, and resulted in coincident changes of both the patterns of impulse origin and heart rate. In addition, we examined spontaneous changes in the patterns of impulse initiation which accompanied beat-tobeat changes in cycle length (sinus arrhythmia). There was close agreement between activation and potential maps over the entire steady state and dynamic range of impulse origin. The data can be explained by the concept of a widely distributed system of functionally differentiated but coordinated atrial pacemakers. (Circ Res 54: 332-347, 1984)

Section: Rationale For Comparing Pdm and Asmmentioning

confidence: 99%

Activation sequence and potential distribution maps demonstrating multicentric atrial impulse origin in dogs.

Boineau¹,

Miller²,

Schuessler³

et al. 1984

“…It ensues from this finding that the presence of two dipoles in the circular medium cannot be inferred from the first derivative of the potential along a circumference exhibiting two maxima and two minima. Here, it will be noted that a distance of several centimeters between current source and sink can actually be observed in the heart during the recovery process (30).…”

Section: Discussionmentioning

confidence: 89%

Current and Potential Fields Generated by Two Dipoles

Ambroggi

Taccardi

1970

The distribution of currents and potentials in a circular conducting medium surrounding two eccentric dipoles was studied to establish how much information on the number, location, and orientation of the dipoles could be deduced from measurements of potential in the medium at various distances from the generators. When a single, eccentric dipole was active, the curve illustrating the distribution of potentials along the boundary exhibited different kinds of asymmetry, which revealed that the dipole was eccentric and gave some information about its orientation. When both dipoles were active, two maxima and two minima, revealing the presence of two generators, appeared along the boundary when the angle between dipole moments was 150° or more. Along internal circumferences two maxima and two minima appeared at smaller angles between dipole moments and the location of the maxima was closely related to that of the dipole anodes. When the dipoles lay on the same diameter and had opposite polarity, the presence of two generators was clearly detectable from boundary measurements, whereas vector representation was zero. These data improve our understanding of electrical signals recorded from the body surface, whether in the form of electrocardiograms, vectorcardiograms, or equipotential contour maps.ADDITIONAL KEY WORDS mathematical-physical models electrocardiography vectorcardiography electromaps• Recent investigations on the distribution of cardiac potentials on the body surface of normal subjects and cardiac patients have shown that multiple maxima and minima are simultaneously present on the chest walls during some phases of the cardiac cycle. During the other phases, only one maximum and one minimum were observed (1-5). The number, location and time-course of surface maxima and minima exhibited typical changes in various heart diseases (6-8).Electrophysiological interpretation of chest maps requires the surface potential patterns to be correlated with the intracardiac location of active fibers at the various instants considered. Knowledge of this correlation may be gained in different ways: (1) The distribution of chest potentials and the location of intracardiac generators can be determined experimenFrom Istituto Simes di Cardiologia Sperimentale, Via Bellerio, 41, Milano, Italy 20161. . Received May 14, 1970; accepted for publication October 6, 1970. tally in the same animal (9); and (2) the distribution of potentials in a conducting medium can be established for any number and location of current generators by physical or mathematical models (10)(11)(12)(13)(14)(15)(16)(17)(18)(19). This paper reports an investigation on the current and potential fields generated by two dipoles located eccentrically in a circular, homogeneous conducting lamina. This model has been chosen because it simulates electrical situations actually occurring in the heart when two excitation waves travel simultaneously in different directions through the ventricular or atrial walls.The distribution of potentials generated by t...

“…Spach and Barr, by demonstrating that potential maxima and minima are not uniformly distributed along depolarization isochrones, 28 ' ^ suggest that current density is likewise unevenly distributed. 29 Plonsey 30 and Corbin and Scher 31 have questioned the uniform double-layer hypothesis as a model of activation.…”

Section: Discussionmentioning

confidence: 99%

A solid angle analysis of the epicardial ischemic TQ-ST deflection in the pig. A theoretical and experimental study.

Richeson¹,

Akiyama²,

Schenk³

1978

The solid angle theory has long been applied to the interpretation of the ECG; however, quantitative evaluation of its applicability has been minimal. We applied solid angle analysis to the interpretation of the TQ-ST deflection during acute ischemia. Five anesthetized pigs were studied 1--3 hours after coronary occlusion. Multiple unipolar tracings were recorded from precisely determined positions on the epicardium overlying the ischemic and normal zones. The geometry of the hearts and ischemic zones was preserved, the margins of ischemia being defined as the outer border of Thioflavin S nonfluorescence. Wax replicas of the hearts with ischemic zones removed were constructed. Solid angles subtended at electrode positions on the replicas were calculated. A linear relationship (r = 0.84 - 0.97, P less than 0.001) was shown to exist between the observed TQ-ST deflection and the calculated solid angle. A small but patterned deviation from exact fit of the TQ-ST deflection with the calculated solid angle led us to investigate the possibility that dipole moment strength (phi) is not confined to the ischemic margins. Computations using idealized heart models with ischemic zones cylindrical and transmural in shape allowed us to distribute phi arbitrarily within the ischemic zone, comparing this predicted pattern of TQ-ST deflection with that observed experimentally. The experimental data appear most consistent with the condition in which phi is distributed over a 1-cm border region during the first several hours of ischemia. We conclude that the solid angle theory provides a rational basis for interpretation of the ischemic TQ-ST deflection; however, phi may be distributed over a marginal zone.