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 configuratio n 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 creat ed by shocks delivered using this configuration. We hypothesized that more effective waveforms could be obtained by varying the distribution of the sh ock current between the two pathways of a three electrode endocardial defib rillation system. In 12 pigs, we compared the characteristics and the defib rillation efficacy of six biphasic waveforms discharged using either a two (RV --> C) or a three (RV --> SVC + C) electrode combination with the follo wing configurations: Configuration 1 (W1): the RV apical coil was used as a cathode and the subc utaneous 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 --> S VC + 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 d uration had significantly lower stored energy DFT than the other waveform. Current distribution between three endocardial electrodes can be altered du ring the shock and generates waveforms with different characteristics. Shoc ks with 75% or more of the current flowing to the RV --> SVC + C required t he lowest stored energy to defibrillate, This method of energy steering cou ld be used to optimize current delivery in a three electrodes system.