Greater cardiac cell excitation efficiency with rapidly switching multidirectional electrical stimulation

Electric field (E) stimulation is widely used in experiments with myocardial preparations and in the clinical setting (e.g., defibrillation). As a rule, stimuli are applied in a single direction, which limits excitatory cell recruitment because myocytes are disposed in different directions and their sensitivity to E depends on the stimulus orientation with respect to the cell major axis. Here, we propose a stimulatory approach, namely rapidly switching multidirectional stimulation (RSMS), in which stimuli are delivered in three directions within the electric refractory period. In populations of randomly oriented isolated rat cardiomyocytes, RSMS doubled the percentage of cells excited by near-threshold E (P < 0.001), which was more than the increase in recruitment in a single direction achieved by doubling E intensity. This effect was similar for monophasic and biphasic pulses, but for the latter, a given percent recruitment was obtained with 20-30% lower E intensity ( P < 0.01), so that RSMS with biphasic pulses allowed at least 60% reduction of E intensity for recruitment of >70% of the cells. RSMS can be applied to improve stimulation efficiency in experiments with isolated cardiac myocytes, and may be a promising alternative for decreasing shock intensity requirements for cardioversion and defibrillation.