Transverse Spread and Longitudinal Dissociation in the Distal A-V Conducting System

Abstract

Isolated preparations of portions of the canine intraventricular conducting system were studied by microelectrode techniques in order to determine the nature of transverse spread and longitudinal dissociation of impulses in bundle branches and false tendons. Driving stimuli were delivered to an eccentric location on normal conducting tissue, and the arrival times of the propagating impulses were mapped along the length and width of the bundle branch, or along the false tendon ipsilateral and contralateral to the site of stimulation. The difference between the arrival times on the two sides was found to decrease progressively as a function of distance from the site of stimulation, the data suggesting that transverse spread of impulses involves propagation through transverse crossover points between the longitudinally oriented conducting elements. Impulses originating eccentrically became uniformly conducted across the transverse axis of bundle branches 8-15 mm from the level of the stimulating electrode, and of false tendons 2-4 mm from the stimulus site. True longitudinal dissociation, producing conduction maps different from those representing normal transverse propagation, was seen occasionally in tissue having longitudinally oriented strips of abnormal tissue. However, early premature stimulation commonly resulted in longitudinal temporal dissociation of the premature responses, possibly due to functional block in the transverse crossover fibers.

Effect of External Potassium and Acetylstrophanthidin on Conduction Velocity of Isolated Canine Purkinje Fibers

“…After equilibration to a solution, the conduction time remained stable at the same values without change. Myerburg et al (5) reported that there is dissociation of transverse and longitudinal spread of excitation in the false tendon which may distort conduction time measurement, but the placing of stimu lating and recording electrodes and the stimulus strength used in this study may be enough to eliminate the dissociation of excitation.…”

Electrophysiological effects or procainamide in acute and healed experimental ischemic injury of cat myocardium.

“…This selection process was carried out in order to have a population of AMI cells which had resting potentials and upstroke velocities comparable to those of healed cells from HMI preparations. Standard microelectrode techniques, previously reported in detail, were used (Myerburg et al, , 1973.…”

“…Premature stimuli were delivered at 2.0 times late diastolic threshold strength, and diastole was scanned as previously reported (Myerburg et al, , 1972(Myerburg et al, , 1973. In those preparations in which it was not possible to initiate sustained ventricular activity by premature stimulation, we determined the effects of drug on action potential duration, local refractory period, upstroke velocity, and resting membrane potential.…”

“…Data were recorded photographically from an oscilloscope screen, using techniques which we have previously reported (Myerburg et al, 1972(Myerburg et al, ,1973, and dV/dt max , action potential duration, and local refractory periods were measured on-line Gelband et al, 1970). Statistical analyses were carried out using a two-tailed, twosample t-tests.…”

A cause of paired ventricular extrasystoles.

“…Some recent data in animal experiments suggests that longitudinal dissociation occurs in the intraventricular conduction system. [22][23][24][25] In figure 5, …”