Induction by direct current pulse versus 50-Hz pacing on ventricular fibrillation and defibrillation

Ventricular fibrillation (VF) induced by different modes of induction may have different characteristics and defibrillation thresholds. This study compares the cycle lengths and defibrillation of VF induced by direct current (DC) pulses vs 50 Hz. We compared induction by DC pulses and 50-Hz pacing in this single-centre observational study of 259 consecutive patients with implantable cardioverter defibrillators in 2007-2008. Patients with inadequate defibrillation safety margin (DSM), defined as unsuccessful defibrillation at 25 J, were identified. Of the 259 patients, 132 underwent induction with DC pulses and 127 with 50-Hz pacing. DC pulses induced VF of shorter cycle lengths (207 +/- 16 vs 231 +/- 24 ms, p <0.001) compared to 50-Hz pacing. There were 17 patients (6.6%) with inadequate DSM-13/132 (9.8%) with DC pulse vs 4/127 (3.1%) with 50-Hz pacing (p <0.001). The induced VF cycle lengths were shorter in patients with inadequate DSM (186 +/- 25 vs 221 +/- 21 ms, p <0.001). On multivariate analysis, only the induced VF cycle length (p = 0.002) was independently associated with inadequate DSM. VF of shorter cycle lengths is independently associated with inadequate DSM. DC pulses are associated with greater proportion of patients with inadequate DSM as it induces VF of shorter cycle lengths compared to 50-Hz pacing.