Circus movement in rabbit atrial muscle as a mechanism of tachycardia. II. The role of nonuniform recovery of excitability in the occurrence of unidirectional block, as studied with multiple microelectrodes.

Abstract

Periods of tachycardia were induced in isolated segments (15 X 15 mm) of rabbit left atrium by local application of a properly timed premature stimulus. We used a special device for multiple synchronous microelectrode recordings of responses of more than 100 fibers during the initiation of tachycardia. We clearly demonstrated circus movement of the impulse through a small area of atrial muscle as the underlying mechanism. The premature impulse was conducted antegrade in only one direction, whereas in the other directions antegrade conduction failed. The local responses of the fibers in the blocked area served as a temporary obstacle for return of the premature impulse. When these fibers recovered their excitability before extinction of the premature impulse, they were reentered in a retrograde direction, and the impulse traveled in a circular route. During the propagation of a premature beat, local block, which set the stage for circus movement, was caused by nonuniform recovery of excitability of the atrium. We related the spread of activation of a premature impulse to the naturally occurring spatial dispersion in refractory periods and found that local conduction block invariably was associated with an area of delayed restoration of excitability. Artificial induction of differences in refractory periods by regional application of carbamylcholine made it clear that a disparity in refractory periods of only 11-6 msec between adjacent areas may be sufficient to cause local conduction block of a properly timed premature impulse.

The effect of acute coronary artery occlusion on subepicardial transmembrane potentials in the intact porcine heart.

“…Dispersion of recovery times of ischemic myocardium, slow conduction and the presence of local conduction blocks may set the stage for re-entry. '4 [32][33][34] Recent studies have emphasized the relationship between delayed and fragmented subepicardial activation and the onset of ventricular arrhythmias5 7,25,30,35,36 Our observations re-emphasize these well-recognized arrhythmogenic factors but also bring attention to the arrhythmogenic capability of the graded response of the ischemic myocardium. Depending on stimulus strength and the length of the preceding cycle, the ischemic action potential can vary from a small local response to large amplitude action potential capable of a regenerative response.…”

Helicoidal instability of a scroll vortex in three-dimensional reaction-diffusion systems

“…We show that the obtained instability persists even beyond the meander core instability of two-dimensional spiral wave. [5], and many others. These seemingly unrelated phenomena share a common feature: they often allow for a description within the framework of two-component reaction-diffusion type systems, for which spiral solutions are generic.…”

“…In Fig. 3 we have plotted the real and imaginary parts of the eigenvalue λ versus k, both for the theoretical prediction given by (5), and for the results of the simulations. As we have predicted, the observed instability of the filament with initial perturbation of a finite k appears to be substantially stronger than the twodimensional core meander instability ( k = 0 ).…”

Modulated Dispersion Explains Changes in Arrhythmia Vulnerability During Premature Stimulation of the Heart

“…The essential components of the substrate, such as nonuniformities of recovery [2][3][4] and tissue anisotropy, 5,6 are thought to remain unchanged during a premature beat. Accordingly, the increase in arrhythmia vulnerability associated with multiple premature stimuli delivered at progressively shorter coupling intervals is thought to result from shortening (ie, similar to "peeling back" 7 ) of refractoriness at the pacing site, allowing capture of subsequent stimuli at increasing degrees of prematurity.…”