Defibrillation Threshold Varies During Different Stages of Ventricular Fibrillation in Canine Hearts

BackgroundRecent studies have shown that short duration ventricular fibrillation (SDVF) and long duration ventricular fibrillation (LDVF) are maintained by different mechanisms. The objective of this study is to evaluate how the defibrillation threshold (DFT) varies over the duration of fibrillation since the mechanism of VF maintenance changes as VF progresses.MethodsTwelve canines were randomly divided into two groups (Group A and B, n = 6 each). DFTs were measured three times in each group: SDVF (20 s), LDVF (3 min in Group A and 7 min in Group B) and the first episode of refibrillation after successful defibrillation for LDVF. Two 64-electrode baskets used to globally map the endocardium were deployed into the left ventricle and right ventricle, respectively.ResultsLDVF-DFT in Group A was significantly higher than that of Group B (628 ± 98 V vs 313 ± 81 V, P < 0.001). In Group B, the DFT of refibrillation was significantly increased compared with the LDVF-DFT (570 ± 199 V vs 313 ± 81 V, P = 0.035) but did not differ from the DFT of refibrillation in Group A (570 ± 199 V vs 638 ± 116 V, P = 0.39). Highly synchronised activation patterns on the left ventricular endocardium were observed between 3 and 7 min of LDVF in Group B but not within 3 min-LDVF in Group A or during refibrillation in each group.ConclusionsDFT varied during different stages of VF. The highly synchronised activation patterns exhibiting after 3 min VF might contribute to the decreased LDVF-DFT.