Delayed activation and retrograde propagation in cardiac muscle: Implication of virtual electrode effects

Point cathodal stimulation of cardiac tissue was shown previously to produc e both a dog-bone shaped virtual cathode transverse to the muscle fibers an d two longitudinal virtual anodes. We hypothesize that virtual anodes can c ause a region of delayed activation, separating two regions of early activa tion caused by the virtual cathode. Using a high-density electrode array in 42 superfused epicardial slices from 14 canine left ventricles, we observe d regions of early and delayed activation and different pathways of retrogr ade propagation corresponding: to the earlier patterns. Retrograde propagat ion was seen from the transversely located early activation area through ar eas of delayed activation toward the cathode, and from the early activation area toward the cathode directly. These pathways caused a wide dispersion in the direction of retrograde propagation (2 degrees+/-31 degrees, n=179. relative to the fast axis of threshold activation, radial velocity: 0.5+/-0 .2 m/s, n = 95, in 12 slices from 8 hearts with stimuli of 330 mus, 0.8-30 mA). Delayed activations were observed 0 degrees+/-6 degrees (n=32) from th e axis in 23 maps (at differing stimulation strengths) recorded in 13 slice s from 10 hearts. We conclude that point cathodal stimulation induce delaye d activation along the fiber axis and retrograde propagation both along and transverse to the axis. (C) 2000 Biomedical Engineering Society. [S0090-69 64(00)00111-9].