DOES AN SVC ELECTRODE FURTHER REDUCE DFT IN A HOT-CAN ICD SYSTEM

Pectorally implanted ICDs that defibrillate with the RV electrode and the ICD housing have gained clinical acceptance, However, it is still debatable whether adding an SVC electrode connected to the housing wil l further reduce the threshold of defibrillation (DFT). This study uti lized eight pigs. DFTs were measured with a 50 V step-down protocol st arting at 650 V (20 J). Shock strength for 50% success (E50) was estim ated with the average of three reversals. In addition to a dummy devic e, Lead I (Pacesetter Models 1558 and 1538) or Lead II (Endotak 72) we re used. Leads I are active fixation, true bipolar sensing with 5-cm s hocking coils. Lead II has an integrated bipolar sensing with a 4.7-cm RV and 6.9-cm SVC shocking coils. A 95 mu F defibrillation system was used to deliver a 44% tilt tuned biphasic 1.6/2.5 ms waveform, and to measure lead impedance. The RV electrode was the anode during phase I . With Lead IRV-->CAN the DFT was 531+/-75 V (13.6+/-3.8 J) and the E5 0 was 496+/-89 (12+/-4.3 J). These were not significantly (NS) differe nt than the DFT for RV-->CAN and SVC which was 518+/-84 V (13+/-4.2 J) or the E50 which was 476 +/-84 V (11+/-3.9 J). Similar results were o btained with Lead II. Despite a decrease in lead impedance there was n o apparent benefit from the addition of the SVC electrode. Lead I prov ided equivalent DFT performance to Lead II.