Excitability for anodal stimulation reached its maximum immediately after the absolute refractory period, exceeding cathodal excitability, and the dip phenomenon is likely due to electrode arrangement.
Investigations are reported in which the excitability cycle of the dog's heart was tested successively by unipolar anodal and cathodal square wave shocks as well as by bipolar stimulation. The classical view that excitability decreases smoothly during the relative refractory phase was substantiated. The excitability for anodal stimulation reached its maximum of the cardiac cycle immediately after the absolute refractory period and exceeded cathodal excitability at that moment. Evidence is presented that the dip phenomenon described by Orias, Brooks and their associates is due to their arrangement of driving and testing electrodes. The coincidence of the dip phenomenon with the vulnerable period may be related to simultaneous spreading of two fronts of activation from cathode and anode of bipolar electrodes which would create favorable conditions for reentry.
Dam et al. (Thu,) conducted a other in Excitability cycle of the dog's left ventricle. Unipolar anodal, cathodal square wave shocks, and bipolar stimulation was evaluated on Excitability cycle. Excitability for anodal stimulation reached its maximum immediately after the absolute refractory period, exceeding cathodal excitability, and the dip phenomenon is likely due to electrode arrangement.