Woven Wire Patches Are Superior to Solid Disks for Subcutaneous Electrodes: Implications for Active Can Defibrillation

Abstract

The housing of the implantable cardioverter defibrillator (ICD) is being considered for a remote electrode to replace the conventional subcutaneous woven wire patch. It is not clear that the solid smooth and rigid metal surface of the ICD housing will provide the same performance as does the woven wire patch. We compared a solid titanium disk to a titanium woven wire patch for defibrillation performance in a canine model. The patch had a smaller outline area, a slightly smaller conductive perimeter, and slightly less of a small feature surface area than did the disk. The remote electrode (disk or patch) was inserted at the point of maximal apical cardiac impulse. A commercially available endocardial electrode was placed in the right ventricle (RV). Conventional biphasic shocks (140-microFrench capacitor and 65% tilt) were delivered between the RV and subcutaneous electrode. The patch had significantly lower resistances than did the disk (81.6 +/- 8.0 omega vs 90.0 +/- 11.6 omega P < 0.006). The patch also had significantly lower stored energy defibrillation thresholds than did the disk (8.0 +/- 2.6 J vs 9.3 +/- 3.3 J, P < 0.007). In spite of smaller values for every geometrical dimension, the woven wire patch out performed the solid disk for defibrillation with conventional biphasic waveforms. Since the ICD housing is typically smooth titanium, the use of waveforms better suited for the active can configuration may deserve a systematic evaluation.