Mapping of reentry in a thin sheet of canine myocardium

Sustained reentry was initiated in a thin sheet of normal canine myocardium (40×40×1 mm) using a cross-shock stimulation protocol. A line stimulus applied to one side of the preparation was followed, some 175 ms later, by a field stimulus in the orthogonal direction. Mapping was carried out using a 121-unipolar electrode array and the intrinsic deflection at each site was used to plot activation isochrones. A given cycle of reentry was illustrated as a set of curved isochrones circling around an area of quasi-silent myocardium characterized by very low potentials and the absence of clear intrinsic deflections. A similar behavior was observed in a model study based on a sheet of cardiac fibers. The model results suggest that reentry occurs around a zone of unidirectional conduction block which is circumscribed, at each turn, by the displacement of the tip (extremity) of the isochrones across the sheet surface