Abstract 192: Defibrillation Strategy with Postshock Synchronized Pacing in Excitable Gaps
Introduction: It was previously demonstrated that ventricular fibrillation (VF) can be synchronized with a novel spatiotemporal excitable gap pacing (SyncP) technique using low-energy pacing pulses that causes pace termination of VF. Therefore, we hypothesize that a spatiotemporally controlled (STCD) defibrillation strategy using defibrillation shocks followed by SyncP may be effective in defibrillation efficacy improvement.
Methods and Results: We explored the STCD effects in 10 isolated rabbit hearts (n=10) with optical mapping of the anterior wall in LV. Optical recording guided real-time detection and stimulation of spatiotemporal excitable gaps was performed. SyncP was shown to cause wavefront synchronization as indicated by a decreased number of phase singularity points (p<0.0001) and reduced spatial dispersion of VF cycle length (p<0.01). After a defibrillation shock delivery, an isoelectrical window (IW) was present and the duration of the IW was a function of the shock strength. When the reference site detected the earliest activation (early site) of the reinitiated VF during IW, a 5-mA electric stimulus was delivered from the pacing electrode to depolarize the excitable gap, creating a functional block to stop VF propagation or change the propagation timing/pattern for VF termination. The location of the early site varied, however, about 80% arose from the right side of LV anterior wall close to apex, with the arrangement of the defibrillation anode electrode in the RV and cathode against the posterior wall. For 90% of the episodes where the reference site accurately detected the early site location, the SyncP pacing electrode successfully administered pacing in the excitable gap after low-energy shock delivery. VF was demonstrated to be successfully terminated by the STCD defibrillation with low-energy shock and pacing in the excitable gaps to cause functional block for reinitiated VF propagation in heart tissues.
Conclusion: We implemented the concept of post-shock synchronized pacing in excitable gaps by a real-time feedback mechanism. Further optimization of this technique may prove effective in improving the defibrillation efficacy by synchronized VF activation.