Cycle length characteristics differentiating non-sustained from self-terminating ventricular fibrillation in Brugada syndrome

AIMS: Limited information is available on self-terminating (ST) ventricular fibrillation (VF). Understanding spontaneous fluctuations in VF cycle length (CL) is required to identify arrhythmia that will stop before shock. Using Brugada syndrome (BS) as a model, the purpose of the study was to compare ST-VF and VF terminated by electrical shock and to look for spontaneous fluctuations in ventricular CL. METHODS AND RESULTS: Occurrence of ST-VF and VF was studied in 53 patients with 46 VF episodes: (i) spontaneously, (ii) during defibrillation threshold testing, (iii) during programmed ventricular stimulation (PVS). Fifteen presented ST-VF (average duration 25 s): 11 during PVS, 1 during defibrillation threshold testing, and 3 spontaneously (at device interrogation). Self-terminating ventricular fibrillation was compared with 31 VFs terminated by electrical shock. Mean ventricular CL was longer (192.5 ± 22 vs. 149 ± 19 ms) (P < 0.0001) and CL became longer or did not change in ST-VF (187 ± 28 vs. 200 ± 25 ms) (first vs. last CL)(NS) in contrast with progressively shorter CL in electrical shock-terminated VF (177 ± 14.5 vs. 139 ± 12 ms) (first vs. last CL before electrical shock) (P < 0.0001). Ventricular fibrillation had more CL variability (average 16.4 ± 6.5 ms) for the first 50 beats than ST-VF (average 4.08 ± 2) (P < 0.0001). Cycle length range for the first 50 beats was 9.6 ± 1 ms for ST-VF and 44 ± 15 for VF (P < 0.002). CONCLUSION: Self-terminating ventricular fibrillation in BS was not rare (28%). Ventricular CL was longer and progressively increased or did not change in ST-VF compared with electrical shock-terminating VF. Cycle length variability and CL range could differentiate VF and ST-VF within the first 50 beats. These parameters should be considered in the algorithms for VF detection and termination.