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We quantified ventricular fibrillation (VF) activation rate, conduction block, and organization transmurally in pigs and dogs, whose transmural Purkinje distribution differ. In six pigs and five dogs, 75 to 100 plunge needles, containing four electrodes for the right ventricle (RV) and six electrodes for the left ventricle (LV) and septum, were inserted in vivo. Six VF episodes were electrically initiated and allowed to last for 47 to 180 seconds. From the FFT power spectra, dominant frequency (DF), an estimate of activation rate, and incidence of double peaks (DPI), an estimate of conduction block, were calculated every 8 ms at each electrode. DF was highest at the epicardium and lowest at the endocardium, whereas DPI was highest at the endocardium and lowest at the epicardium for the entire LV and the RV base in both pigs and dogs for the first 70 seconds of VF. This distribution changed little throughout the first 3 minutes of VF in pigs but reversed in dogs by 2 minutes of VF. In conclusion, estimated activation rates and conduction block incidence during VF are not uniformly distributed transmurally. During the first minute of VF, the faster activating LV base epicardium exhibits less estimated block than the slower endocardium, raising the possibility that faster activating epicardium generates wavefronts that drive the endocardium early during VF. Constancy of this pattern in pigs but its reversal by 2 minutes in dogs is consistent with the hypothesis that activation during later VF is driven by Purkinje fibers.

Estimated Global Transmural Distribution of Activation Rate and Conduction Block During Porcine and Canine Ventricular Fibrillation