Prospective evaluation of initially ineffective defibrillation pulses on subsequent defibrillation success during ventricular fibrillation in survivors of cardiac arrest

The effect of initially ineffective defibrillation pulses on subsequent defibrillation success is not known. Therefore, the voltage, current and energy at the defibrillation threshold were compared with the defibrillation rescue pulse voltage, current and energy that terminated ventricular fibrillation when an ineffective pulse just below the defibrillation threshold had been used initially. This lower amplitude ineffective pulse was termed a “subdefibrillation threshold” pulse. The pulse that restored sinus rhythm after the subdefibrillation threshold pulse was delivered was termed the “subdefibrillation threshold rescue pulse.” This comparison was undertaken, intraoperatively, in 14 out-of-hospital cardiac arrest survivors using a sequential-pulse catheter-patch defibrillation system. Each of the 14 patients required higher voltage, current, delivered energy and stored energy for defibrillation with the subdefibrillation threshold rescue pulse than with the defibrillation threshold pulse. The defibrillation threshold voltage was 451 ± 127 volts compared with a subdefibrillation threshold rescue voltage of 585 ± 147 volts (p < 0.00002). The defibrillation threshold current was 5.5 ± 2.4 amps compared with a subdefibrillation threshold rescue current of 7.2 ± 2.7 amps (p < 0.00001). Delivered and stored energies were 10.9 ± 7.4 and 12.3 ± 7.2 J, respectively, for the defibrillation threshold pulse and were 17.6 ± 9.4 J (p < 0.00002) and 20.5 ± 9.3 J (p < 0.00005), respectively, for the sub-defibrillation threshold rescue pulse. It is concluded that the risk of requiring considerably higher energies than anticipated for defibrillation must be incurred, should defibrillation fail because of an initially insufficient defibrillation pulse. Such an occurrence might result in death should the energies necessary for defibrillation exceed the output limits of the implantable device.