Is ventricular fibrillation interval an indicator of electrical defibrillation threshold?

To clarify whether peak-to-peak interval of the fibrillation wave (VF interval) during VF is an independent indicator of defibrillation efficacy, we measured the transcardiac DFT, VF intervals of the surface and local ECGs (lead II and the right ventricle), and the ERP in 82 open-chest dogs. Both VF intervals showed a negative correlation with heart weight (surface: r = -0.358 [P < 0.005]; local; r = -0.349 [P < 0.005]). DFT was 2.0 +/- 0.7 A and positively correlated with heart weight (r = 0.453 [P < 0.0001]). ERP did not show a significant correlation with heart weight. DFT was negatively correlated with VF interval (vs surface VF interval: r = -0.568 [P < 0.0001]; vs local VF interval: r = -0.504 [P < 0.0001]), but showed only a weak negative correlation with ERP (r = -0.314 [P < 0.005]). Even after allowing for the dependency of DFT and VF intervals on heart weight (normalized to a 100-g heart), the correlation between VF interval and DFT was still significant (vs surface VF interval: r = -0.487 [P < 0.0001]; vs local VF interval: r = -0.414 [P < 0.0002]). These results suggest that VF interval is an indicator of DFT in intact hearts that have not received pharmacological intervention.