IMPROVED INTERNAL DEFIBRILLATION SUCCESS WITH SHOCKS TIMED TO THE MORPHOLOGY ELECTROGRAM

Background-A previous retrospective study by our group suggested that shocks timed to the upslope of the shocking lead electrogram improved defibrillation efficacy. The goal of this study was to prospectively d etermine whether defibrillation threshold could be reduced by use of a n algorithm that timed shocks to the upslope of coarse ventricular fib rillation (test treatment) compared with shocks delivered asynchronous ly after 10 seconds of fibrillation (control treatment). Methods and R esults-Ten pigs were instrumented with a 3-lead system for internal de fibrillation, Initial estimates of the energy required to achieve defi brillation E-50 for both treatments were made by an up/down method, Su bsequently, additional shocks at V-50+/-10% and V-50+/-20% were given for each treatment to obtain data points at higher and lower intensiti es. Probability-of-success curves were estimated for both treatments b y the best-fit method. Energies required were significantly lower for the timed shocks than for the asynchronous shocks (P<0.001), E-80 was reduced 15.5%, from 27.1+/-2.5 to 22.9+/-1.8 J (P<0.002), The width of the probability-of-success curve (E-80-E-20) for the test treatment w as also significantly narrower than that for the control treatment (7. 1 +/- 0.9 versus 10.8 +/- 1.7, P<0.01), Normalized curve width (E-80-E -20)/E-50 was decreased from 51+/-5% of E-50 for control shocks to 37/-4% of E-50 for synchronous shocks (P<0.02), Conclusions-In this mode l, defibrillation threshold is lower and more deterministic when shock s are timed to the upslope of the shocking lead electrogram, If a simi lar reduction is observed in humans, shock timing may lower defibrilla tion threshold and simplify programming of shock intensity.