Separation of ventricular tachycardia from ventricular fibrillation using paired unipolar electrograms

In third-generation implantable antitachycardia devices, immediate defibrillation is necessary for ventricular fibrillation (VF) while lower-energy therapies convert many ventricular tachycardias (VTs). Precise distinction between true VF and VT is required if tiered-therapy is to be effectively utilized. To separate VF from VT, this study employed a measurement to quantify the coherence between two unipolar electrograms from the same catheter, where incoherence between signals indicates VF. A normalized cross correlation (CC) measured similarity, and standard deviation (STD) and interquartile range (IQR) of the CC measured consistency for sinus rhythm (SR), VT, and VF passages from 10 patients. Patient-independent STD thresholds of 0.15-0.25 and IQR thresholds of 0.3-0.6 provided 100% sensitivity and 100% specificity. This method was able to successfully separate VF from coherent rhythms (SR,VT). Proper distinction of VT would allow defibrillation to be deferred for consideration of lower energy therapies, providing significant energy savings.