Energy steering of biphasic waveforms using a transvenous three electrode system

The optimal electrode configuration for endocardial defibrillation is still a matter of debate. Current data suggests that a two path way configuration using the right ventricle (RV) as cathode and a common anode constituted by a superior vena cava (SVC) and a pectoral can (C) is the most effective combination. This may be related to the more uniform voltage gradient created by shocks delivered using this configuration. We hypothesized that more effective waveforms could be obtained by varying the distribution of the shock current between the two pathways of a three electrode endocardial defibrillation system. In 12 pigs, we compared the characteristics and the defibrillation efficacy of six biphasic waveforms discharged using either a two (RV --> C) or a three (RV --> SVC + C) electrode combination with the following configurations: Configuration 1 (W1): the RV apical coil was used as a cathode and the subcutaneous C as anode (RV --> C). Configuration 2 (W2): The RV was used as cathode and the combination of the atriocaval coil (SVC) and the subcutaneous C as anode (RV --> SVC + C). Configuration 3 (W3): The RV --> C was used for the first 25% of f + and RV --> SVC + C for the remainder of the discharge including f 2. Configuration 4 (W4): The RV --> C was used for the first 50% of f + and RV --> SVC + C for the remainder of the discharge including f 2. Configuration 5 (W5): The RV --> C was used for the first 75% of f + and RV --> SVC + C for the remainder of the discharge including f 2. Configuration 6 (W6): The RV --> C was used for f + and RV --> SVC + C for f 2. As an increasing fraction of the waveform was discharged using the RV --> SVC + C pathways, the impedance and the pulse width decreased while the tilt, the peak, and the average current significantly increased. The waveforms delivered using the RV --> SVC + C configuration for 100% or 75% of their duration had significantly lower stored energy DFT than the other waveform. Current distribution between three endocardial electrodes can be altered during the shock and generates waveforms with different characteristics. Shocks with 75% or more of the current flowing to the RV --> SVC + C required the lowest stored energy to defibrillate, This method of energy steering could be used to optimize current delivery in a three electrodes system.