992-110 Finite Element Analysis of Post-shock Sensing Performance in Transvenous Implantable Defibrillator Lead Systems

Abstract

Post-shock sensing abnormalities have been observed in transvenous (TV) implantable defibrillator (ICD) lead systems. This may be related to the proximity of the sensing and defibrillation (DF) electrodes, and due to local conduction block in areas of high potential gradients. Potential gradients of > 64 V/cm have been shown to cause local conduction block. To study the effect of lead geometry on potential gradient at the sensing circuit following a high voltage shock, a finite element model was constructed to simulate three TV ICD leads: Endotak 60 TM , TVL TM , and Transvene TM . The first two lead systems use integrated bipolar sensing (tip to distal DF coil); the latter uses true bipolar sensing (tip to ring electrode). The model consisted of a three-dimensional, cylindrically symmetric right ventricle, with the lead surrounded by blood except at the distal electrode, which was in contact with myocardium. The model was calculated assuming an applied voltage of 650 V at the distal DF coil, with the proximal DF coil at 0 V. The potential gradient at each point of a 635 to 824 node finite element model was solved using LaPlace's equation, assuming typical values for conductivity of blood (0.01 S/cm) and myocardium 10.002 S/cm). Potential gradient values at the distal sensing electrode were < 30 V/cm in all TV ICD systems. The potential gradient at the proximal sensing electrode in the Transvene TM was < 30 V/cm. Potential gradients of > 64 V/cm (range 64 to 660 V/cm) were seen at all nodes within 3 mm of the distal DF electrode. Nodes adjacent to the sensing circuit in the true bipolarsensing lead had potential gradients < 30 V/cm, whereas the area surrounding the sensing cathode of integrated bipolar systems had potential gradients > 64 V/cm. This model demonstrates: 1) how post-shock sensing performance may be significantly affected by lead geometry; 2) that integrated bipolar sensing systems may be affected more by shock delivery than true bipolar sensing systems