Implantable Intravascular Defibrillator: Evaluation of Defibrillation Waveforms with Inferior Vena Cava Electrode System

Methods: Eight Bluetick hounds (wt = 30-40 kg) were anesthetized and the RV coil (first-phase anode) was placed in the RV apex. The intravascular defibrillator (PICD (R), Model no. IIDM-G, InnerPulse Inc., Research Triangle Park, NC, USA) was positioned such that the titanium electrodes were in the SVC and IVC. Ventricular fibrillation was electrically induced and a Bayesian up-down technique was employed to determine DFT with two configurations: RV to SVC + IVC and RV to SVC. Three waveform tilts (65%, 50%, and 42%) and two second-phase durations (equal to the first phase [balanced] and truncated at 3 ms [unbalanced]) were randomly tested. The source capacitance of the defibrillator was 120 mu F for all waveforms. Results: DFT with the IVC electrode was significantly lower than without the IVC electrode for all waveforms tested (527 +/- 9.3 V [standard error], 14.5 J vs 591 +/- 7.4 V, 18.5 J, P < 0.001). Neither waveform tilt nor second-phase duration significantly changed the DFT. Conclusion: In canines, a totally intravascular implantable defibrillator with electrodes in the RV apex, SVC, and IVC had a DFT similar to that of standard nonthoracotomy lead systems. No significant effect was noted with changes in tilt or with balanced or unbalanced waveforms. (PACE 2011; 34:577-583).