Defibrillation efficacy using high-frequency switching to proportion current among simultaneous shock pathways

Multiple-pathway electrode configurations generally allow improved current distribution over the heart and lower defibrillation thresholds than single-pathway systems. However, current distributions using multiple pathways are largely determined by electrode type and location. We hypothesized that switching the current among multiple pathways at high frequency (HF) could allow the switching duty cycle to control the proportion of time-averaged current flowing in each pathway, thus permitting altered (possibly improved) defibrillation efficacy using the same electrodes and shock waveform.

In dogs, we measured the current (I50) for 50% defibrillation success using catheter electrodes in the right ventricular apex (cathode) and superior vena cava (A-pathway anode) and a subcutaneous patch on the left chest wall (B-pathway anode). In group 1 (N = 7), we measured I50s for shocks that used HF to proportion 10% to 90% of the current to the A-pathway. Shocks with 10% to 30% of the current in the A-pathway had significantly lowr I50s than nonproportioned shocks using all three electrodes. However, the resistance differed among single and simultaneous pathways so energy did not necessarily parallel these changes. In group 2 (N = 6), we measured I50s for shocks to the B-pathway alone, for nonproportioned shocks to A and B, and for shocks that proportioned 80% of the current to the B-pathway using either HF, sequential, or amplitude proportioning methods. All proportioning methods had similar I50s that were significantly lower than the I50 for nonproportioned shocks to A and B and that were comparable to shocks to the B-pathway alone.

Shocks with most current proportioned to the B-pathway had lower defibrillation currents than nonproportioned shocks using both pathways. Thus, defibrillation efficacy was changed by HF proportioning without changing the electrodes or shock waveform. These findings suggest that HF proportioning may be a method to improve defibrillation.