A CRITICAL PERIOD OF VENTRICULAR-FIBRILLATION MORE SUSCEPTIBLE TO DEFIBRILLATION - REAL-TIME WAVE-FORM ANALYSIS USING A SINGLE ECG LEAD

Previous studies have suggested that variations in the underlying vent ricular fibrillation (VF) waveform may be one of the factors responsib le for the probabilistic nature of defibrillation. The heart appeared to be more susceptible to defibrillation at higher absolute VF voltage s (AVFV). This study investigated in an open-chest canine model (n = 8 ), a newly developed system that analyzed the VF waveform in real-time , instantaneously determined the time to shock, and immediately delive red a fixed low energy DC shock. A two parameter tracking technique us ing a running long-term and short-term AVFV average was devised to aut omatically identify a high voltage peak area of the VF waveform, which has been hypothesized to represent a critical period susceptible to d efibrillation. Using a DC shock estimated at the 50% success level, th e performance using this technique in 58 defibrillation trials was com pared to the performance of the conventional method of shocking at a f ixed time (random shock method) in 62 trials. Patch size, electrode lo cation, and discharge voltage were kept constant while VF duration, tr ansmyocardial resistance (TMR), energy delivered, and AVFV at the poin t of shock were measured. Shock energy and current, TMR, and VF durati on were similar with both shock methods. A significantly higher AVFV w as observed for trials performed with the peak shock method (0.66 +/- 0.02 mV) as compared to trials performed with the random shock method (0.25 +/- 0.09 mV) (P < 0.003). Using lead II as the only sensing lead , the success rate was increased in 6 of 8 dogs (75%) with the new met hod. One animal showed identical performance, and one animal a worse p erformance. The overall increase in success rate was 24% using a singl e ECG lead (range 0%-100%; P < 0.04). Our data document that using thi s algorithm a period of high VF voltage can be detected in real-time. The improved success in the majority of animals supports the hypothesi s that a critical period susceptible to defibrillation exists during V F. However, the high AVFV detected using a single ECG lead did not tra nslate to an improved success rate in all animals. This suggests that other factors in addition to the VF voltage measured on a single lead of the ECG are important in characterizing this critical period.