IMPROVED NONTHORACOTOMY DEFIBRILLATION BASED ON VENTRICULAR-FIBRILLATION WAVE-FORM CHARACTERISTICS

The heart has been shown to be more susceptible to defibrillation at a higher absolute ventricular fibrillation voltage (AVFV) measured on t he surface EGG. This study evaluated in a closed-chest canine model (n = 7) the clinical applicability of using a real-time VF waveform anal ysis system using an electrogram defined between the generator can and an RV endocardia! electrode. Under fluoroscopic guidance, superior ve na cava and RV spring coil catheter electrodes n ere inserted through the external jugular vein. A subcutaneous patch was placed on the left chest. A two-parameter tracking algorithm was used to dynamically ide ntify the high AVFV area, and a biphasic shock was triggered synchrono usly at the next peak. The performance of this new peak shock method ( PSM) was compared to the conventional method of shocking at a fixed ti me in 175 paired trials. Five shocks per voltage and five voltages per animal were randomized between the two methods to permit the generati on of sigmoidal dose response curves for the estimation of 50% (E50), 75% (E75), and 100% (E100) success energies, induction of VF and disch arge voltage were kept constant while energy delivered, impedance (R), and AVFV at the point of shock were measured, Energy 18.63 +/- 0.40 v s 8.64 +/- 0.40 J), R (48.60 +/- 0.30 vs 48.59 +/- 0.30 Omega), and cu rrent (7.50 +/- 0.18 vs 7.52 +/- 0.16 A) were not significantly differ ent between trials for either the conventional or the PSM. The time fr om the onset of VF until the defibrillation shock was 7.98 +/- 1.44 se conds, Higher overall successes (46.3% vs 33.1%; P < 0.01) and lower E 50, E75, and E100 were observed for the PSM. Finally, the significantl y higher AVFV (9.12 +/- 0.32 vs 4.73 +/- 0.34 mV; P < 0.0001) with the peak method suggests that the high VF voltage could be detected as it occurred in real-time, The improved defibrillation success supports t he use of this method for nonthoracotomy defibrillation.