PREDICTING THE POTENTIAL GRADIENT FIELD IN VENTRICULAR-FIBRILLATION FROM SHOCKS DELIVERED IN PACED RHYTHM

A method of defibrillation threshold determination that utilizes low-s trength shocks delivered in a benign rhythm would be desirable. Becaus e the two-dimensional epicardial potential gradient (PG) is a shock pa rameter that is Linked to defibrillation, we examined whether the epic ardial PG measured for shocks delivered in paced rhythm could be used to predict the PG for defibrillation-strength shocks delivered in vent ricular fibrillation (VF). In six open-chest pentobarbital-anesthetize d pigs with left ventricular apex and right atrial internal defibrilla tion patches, we measured the epicardial PG field for shocks delivered in paced rhythm and during VF. We determined that there was a Linear relationship between epicardial PG and shock strength for shocks deliv ered in paced rhythm. However, prediction of the PG measured for shock s in VF from those measured in paced rhythm resulted in a statisticall y significant overestimation of the PG in VF. We conclude that, for eq uivalent strength shocks, the epicardial PG field is weaker for shocks delivered in VF. This change in the potential gradient field can have an effect on defibrillation threshold estimates that are based on sho cks delivered in paced rhythm.