Anodal Stimulation - The Intrigue Continues

When cardiac pacing is performed in the bipolar configuration, both the cathode (negatively charged electrode) and the anode (positively charged electrode) are in contact with the myocardium. Myocardial stimulation by the pacing stimulus typically occurs only at the interface with the cathode. This is because (i) given equal sized electrodes, anodal stimulation has a higher threshold compared to cathodal stimulation except for a "dip" at short coupling intervals [1] and (ii) the anode is usually designed as an electrode with a larger surface area making stimulation less likely. However, it has long been known that anodal stimulation is not uncommon with bipolar pacing systems because pacing output is usually programmed well above the stimulation threshold.