DEFIBRILLATION EFFICACY USING HIGH-FREQUENCY SWITCHING TO PROPORTION CURRENT AMONG SIMULTANEOUS SHOCK PATHWAYS

High-Frequency Current-Proportioned Defibrillation, Introduction: Mult iple-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 hyp othesized that switching the current among multiple pathways at high f requency (HF) could allow the switching duty cycle to control the prop ortion of time-averaged current flowing in each pathway, thus permitti ng altered (possibly improved) defibrillation efficacy using the same electrodes and shock waveform. Methods and Results: In dogs, we measur ed the current (I-50) for 50% defibrillation success using catheter el ectrodes in the right ventricular apex (cathode) and superior vena cav a (A-pathway anode) and a subcutaneous patch on the left chest wall (B -pathway anode), In group 1 (N = 7), we measured I(50)s for shocks tha t used HF to proportion 10% to 90% of the current to the A-pathway, Sh ocks with 10% to 30% of the current in the A-pathway had significantly lower I(50)s than nonproportioned shocks using all three electrodes, However, the resistance differed among single and simultaneous pathway s so energy did not necessarily parallel these changes, In group 2 (N = 6), we measured I(50)s for shocks to the B-pathway alone, for nonpro portioned shocks to A and B, and for shocks that proportioned 80% of t he current to the B-pathway using either HF, sequential, or amplitude proportioning methods, All proportioning methods had similar I(50)s th at were significantly lower than the I-50 for nonproportioned shocks t o A and B and that were comparable to shocks to the B-pathway alone. C onclusions: 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 proportionin g without changing the electrodes or shock waveform, These findings su ggest that HF proportioning may be a method to improve defibrillation.