Catheter electrode defibrillation in dogs: threshold dependence on implant time and catheter stability

A catheter-mounted electrode system designed for intracavitary ventricular defibrillation was implanted in the right ventricular apex of 12 dogs. Defibrillation thresholds were obtained in all dogs at the time of implant using an external defibrillator. Roentgenograms obtained 3 weeks after catheter implantation revealed that six dogs had catheters intact at the site of implant (group A) and six dogs had catheters that had dislodged from the original implant site (group B). There were no statistically significant differences (p less than 0.05) in mean body weight or mean defibrillation threshold between group A and group B dogs, respectively, at implant. Defibrillation thresholds were obtained for both groups of animals at 5, 12, and 26 weeks after catheter implantation. At all post implant monitors mean threshold for group B was significantly higher (p less than 0.05) than mean threshold for group A. Moreover, mean defibrillation threshold for both groups had increased by week 5 and remained stable through week 26. Catheter dislodgement increases defibrillation threshold, but does not prevent successful defibrillation. Also, defibrillation threshold increases to a stable value by 5 weeks post implant.